ANATOMY & PHYSIOLOGY SERIES - nutrihealfoundation.com fileuntil we cut one open we would not know why they jump (the grub inside is responsible). But all we find if we ‘cut open’

Lecture 2 – The Cell 1

ANATOMY & PHYSIOLOGY SERIES

LECTURE 2 – A&P

THE CELL – Part 2



CONTENTS

GENERAL INTRODUCTION TO BIOCHEMISTRY

A Basic chemistry Elements and compounds, atoms, atomic weight, isotopes, molecules and chemical bonds, ionic bonds, covalent bonds, hydrogen bonds, chemical

reactions, organic and inorganic compounds

B – Movement in and out of the cell Passive Transport – simple diffusion, dialysis, osmosis,

facilitated diffusion, filtration Active transport – membrane pumps, Endocytosis,

Pinocytosis, Exocytosis

C Inside the Cell Cell Respiration, ATP & High energy bonds, Glycosis,

Krebs Cycle/Citric Acid cycle, Electron transport,

CONCLUSION


GENERAL INTRODUCTION TO BIOCHEMISTRY

Biochemistry is the specialised area of chemistry that deals with living organisms and life processes. Since life itself depends on proper levels and proportions of chemical substances in the cytoplasm of the cell, we must begin to understand what chemical processes underlie such activities as growth, repair, muscle contraction and transmission of nerve impulses. Grasping the basic concepts will provide a platform from which you can understand more fully how the body maintains its structure and carries out its many functions. The simple fact is, without the proper chemicals in the right amounts the cell, and therefore, the body, would die.

In this lecture I am going to be speaking about basic cell physiology. The lecture is really in three parts labelled AC and I would like for you to treat it as such. Each part is essential, and my advice is not to move on until you have a reasonable understanding of the whole picture in each part. All of this lecture is highly relevant to nutrition, disease and health.

A BASIC CHEMISTRY

The title of the first episode of this three part lecture is one of the words still used today to induce fear in students all over the globe Basic Chemistry! We know that every cell in the body contains thousands of different chemicals that are constantly interacting with each other. Different types of body tissue have differing chemical compositions, furthermore, our DNA and RNA are also encoded in chemical form. So the chemical makeup of the cell determines its function/s.

From the moment your food enters your mouth and you begin to mechanically crush and tear and grind it into smaller pieces, chemical activities have already begun with the release of saliva. From there on, the liquid food may be rhythmically shaken by the digestive system, but it is the chemicals and chemical reactions that continue the process of reduction and digestion.

At the end of the digestive processes, we are left with the individual building blocks of whatever food was consumed. These are absorbed through the intestinal wall and immediately sent to the liver which breaks them down further (with more chemicals and chemical reactions) until we are left with very simple components that are now acceptable to the body, in essence the ‘building blocks of the building blocks’. These are made up from the many chemical elements that exist and are now ready for assimilation in the cells.

You may find that some of the subjects covered in this lecture were mentioned in previous lectures, as we believe of this Session: we believe that this repetition will be useful for you to assimilate these basic concepts of Chemistry. If, you are already acquainted with Basic Chemistry, please persevere this introduction may prove useful as revision.


Right from the start it is crucial to realise that no one truly knows what atoms are like – their nature is utterly mysterious. What we can do is observe how these entities we call ‘atoms’ interact – and we find they do so very predictably which has helped us to develop a science that systematises these predictions. But we don’t know what the exact nature of these peculiar particles actually is. Indeed, we don’t really know whether they are particles or waves or some strange mixture of the two. I think this really helps, as many people study chemistry and think ‘I can’t get my head around this’, when in fact neither can the chemists!

Remember the first time you saw Mexican jumping beans – they suddenly leapt in the air. Changing the temperature changes the rate they jump, but until we cut one open we would not know why they jump (the grub inside is responsible).

But all we find if we ‘cut open’ an atom is equally mysterious entities that are predictable but impossible to ‘know’.

Elements and Compounds

The best way to understand chemistry is to become familiar with some of the terms used and what they mean. One of the biggest areas of confusion is in understanding the difference between elements and compounds this is easily achieved if we break them down to see how atoms combine to form an element and how an atoms combine to form a compound.

Anything that has mass and occupies space is matter. So, basically any substance or material around us is matter, and all matter is either made of elements or compounds.

Definition of matter: anything that has mass and occupies space. It may be solid, liquid or gas....

Elements

Definition of an element: substance that is composed of only one type of atom that cannot be broken into simpler constituents by chemical means......

A single atom constitutes an element. So, an atom of hydrogen is also the element Hydrogen. If an element is composed of more than one of the same type of atom (such as all hydrogen atoms), then they are called a molecule, for example, a molecule of hydrogen.

Definition of a molecule: formed when two or more of the same type of atom join together.....


There are about 100 known elements. 26 elements are present in significant quantities in the human body, 11 are called major elements. Four of these are the body’s ‘universal building blocks’ and make up about 96% of the material in the human body. These important 4 are : Carbon (C), Oxygen (O), Hydrogen (H) and Nitrogen (N). The remaining 15 elements are called trace elements and make up less than 0.1% of the body weight. The tissues in the body are mainly made of complex proteins, the ‘building material’ of the body. What is protein? Well, all proteins are made up of amino acids, which are commonly regarded as the building blocks of proteins. There are 20 common amino acids and these are all made of carbon, oxygen, hydrogen and nitrogen, although sometimes Sulphur (S), Phosphorus (P) and Iron (Fe) may be present too. Think about this for a moment. Predominantly from 4 chemical elements, 20 amino acids are formed and these can make any protein that the body requires. The only comparison that I can think of is our own alphabet of 26 letters. Each letter is only made up of perhaps three, maybe four strokes of a pen, and yet from just 26 letters we have constructed novels, encyclopaedias, almost never ending written communications.

Hydrogen = H

(Metals) Nonmetals) Sodium = Na Oxygen = O

Potassium = K Carbon = C

Calcium = Ca Nitrogen = N

Magnesium = Mg Phosphorus = P

Iron = Fe Chlorine = Cl

Sulphur = S

Compounds

Definition of a compound: a chemical combination of two or more different types of elements (atoms)....

So, as we have the joining of the same types of elements or atoms to form molecules, we now have the joining of different types of elements or atoms to form compounds. For example, if we join a carbon atom with 2 oxygen atoms, the molecule formed is the compound CO2, (carbon dioxide).


Atoms

Definition of an atom: the smallest particle of a chemical element that retains the properties of that element; particles that combine to form molecules (chemical building blocks)....

Do these chemical elements just kind of ‘hang around together’? Does a carbon molecule decide he is ‘attracted’ to an oxygen molecule, so they gaily hold elemental hands and stick together? What is a carbon molecule anyway? Let’s find out.

Most people have heard of an atomic bomb. You may know that by splitting an atom in half, enormous amounts of energy is released.

Well, all the elements are made up of atoms. Atoms, by definition, are ‘indivisible’ and when they were discovered they were seen as the ultimate unit of all matter. Some time later it was discovered that you could in fact divide these units into subatomic particles. This is the extent of our current knowledge but, as I think you will see, even at this minuscule level of physical matter we find stark reflections of much larger things!

As we have seen, Atoms are the ultimate building blocks of all matter and all elements, the building blocks of everything else, are made of atoms. At this stage it would be useful for you to refer to a text book and look at a diagram of an atom. It may appear similar to a solar system in space, with the sun in the middle and planets travelling around this sun in fixed orbits, held in position by the attraction of the sun. That gives you a model of how an atom looks. The sun of the atom is called the nucleus. The sun in our solar system, around which all planets orbit, could be considered as our nucleus. The ‘planets’ orbiting the nucleus of the atoms are called electrons (e) and these electrons have a negative electrical charge and some of them form a ‘cloud’ or field surrounding the denser nucleus. The negatively charged electrons have fixed orbits called energy shells. These energy shells can only hold a certain number of electrons. The innermost energy shell can hold 2 orbiting electrons, the 2 nd energy shell can hold 8, the 3 rd can hold 18, and the 4 th can hold 32. The electrons will always fill the inner energy shells first, before moving outwards to the next energy shell.

Nucleus

An Electron

A proton

A Neutron


The nucleus is made up of two particles. These are protons (p+) which have a positive charge and neutrons that have a neutral charge, or no charge. The number of protons directly equals the number of electrons, and this characteristic decides what element that atom will be. The number of protons therefore is the atom’s identity tag and is called the Atomic number (the atom’s personal number). This number is usually placed at the top right of the element’s symbol. For example, C 6 identifies the element Carbon, and its atomic number is 6. This means that it has 6 positively charged protons in the nucleus and therefore 6 negatively charged electrons orbiting the nucleus. Because opposites attract, the number of positive protons to negative electrons has to be equal otherwise the attraction will be out of balance. As we have 6 electrons, they will fill the energy shells appropriately, with 2 filling the 1 st shell, leaving 4 to occupy the 2 nd shell. So the atomic number not only tells us how many protons, and therefore how many electrons, there are, but also what the element is, characterised by the unique number of protons, e.g. C 6 as no other element will have this number. However, there are several different types of carbon. These are like ‘non identical’ twins, which are twins from two separate eggs, obviously from the same mother and father and obviously related.

Summary The picture of an atom is very much like our own solar system. First we have the nucleus, which holds the protons and neutrons, then we have our electrons, in organised energy shells, which constantly orbit the nucleus at set distances. Each energy shell can only hold a certain number of electrons in orbit. The 1st holds 2, the 2nd holds 8, the 3rd holds 18 and the 4th holds 32. The number of electrons is equal to the number of protons, to balance the attractions and decide what element it is.

No two elements have the same number of protons/electrons. This number, therefore, is its identity tag and is called the atomic number: e.g. Carbon’s atomic number is 6 because it has 6 protons and 6 electrons while Oxygen’s atomic number is 8, as it has 8 protons and 8 electrons.


Atomic Weight

Definition of atomic weight: the number of protons plus the number of neutrons in an atom of an element.....

Another ‘tool’ that is important to know about is the atomic weight (not to be confused with the previously mentioned atomic number). This is usually written at the bottom right of the letter. Only the protons and neutrons are seen to actually have any relevant mass, and so the atomic weight, also referred to as the atomic mass number, is calculated by adding the number of protons to the number of neutrons. In chemistry books the atomic weight will be written accurately, but it is common practice to round them up to the nearest whole numbers. If you look at hydrogen (H), for example, you will find that its atomic number (at the top, in this case – H 1 ) is 1 and indicates that it has 1 proton and 1 electron. Its atomic weight is 1. What does that tell us?

Remember that if you add the number of protons to the number of neutrons you get the atomic weight. Well in this case we want to calculate how many neutrons there are, so what we do is take the atomic weight and subtract the atomic number and this will equal the number of protons occupying the nucleus with the protons:

Atomic Weight Atomic Number = Number of Neutrons

(No. of Protons + No. of Neutrons) (No. of Protons) = Number of Neutrons

Let’s use Hydrogen, Carbon, Oxygen and Phosphorous as examples.

• Hydrogen Atomic Weight = 1 Atomic Number = 1

1 1= 0. Therefore Hydrogen has no neutrons.

• Carbon Atomic Weight = 12 Atomic Number = 6

12 6 = 6. Therefore Carbon has 6 neutrons.

• Oxygen Atomic Weight = 16 Atomic Number = 8

16 8 = 8. Therefore Oxygen has 8 neutrons.

• Phosphorous Atomic Weight = 31 Atomic Number = 15

3115 = 16. Therefore Phosphorous has 16 neutrons.


Isotopes

Definition of an isotope: atoms with the same atomic number but different atomic weights...

Not all the atoms of an element have the same number of neutrons, (although they do always have the same number of protons). Isotopes are forms of an atom with a different number of neutrons and therefore, a different atomic weight. For example, Carbon, we know, has an atomic number, or name tag, of 6. Anything with the atomic number of 6 must be carbon. However, carbon has two atomic weights of 12 and 13. If you subtract the atomic number from the atomic weight, you have the number of neutrons in the nucleus with the protons. What we find is that carbon has one with 6 neutrons and one with 7. Both are carbon because their atomic number is 6 but they are equivalent to being nonidentical twins. These very important elements are called isotopes (‘iso’ means same, ‘tope’ means place, which gives the meaning that they are both in the same place in the periodic table).

While the number of neutrons does not change the chemical properties of matter to any significant degree, there can be too many or too few neutrons for the atom to be stable – and unstable atoms fall apart forming smaller atoms – a process we call radioactive decay – usually releasing a burst of radioactivity.

We a have already touched molecules slightly, but lets continue now by looking at how atoms bond together to form molecules and compounds.

Molecules and chemical bonds

Definition of a chemical bond: a force of attraction that binds a molecule’s atoms together. Forming a chemical bond often requires energy, breaking a bond often releases energy.

Simply speaking, molecules are two or more atoms bonded together. Atoms bond together to make themselves more stable, to find a natural equilibrium. Some elements are highly reactive on their own and so are bonded to something else to stabilise them, while other elements are quite happy on their own.

Let’s take a look at what makes one element reactive and another not, and at what ‘bonding’ means.

Types of chemical bonding:

1) A Hydrogen bond occurs when 2 atoms associate with a hydrogen atom. Oxygen and nitrogen commonly form hydrogen bonds.

2) An ionic bond (electrovalent bond) formed by transferring of electrons from one atom to another.

3) A covalent bond form when atoms share pairs of electrons.


Helium (He) is a very nonreactive element for very simple, sound reasons. Helium’s atomic number is 2, therefore it has 2 protons and 2 electrons which fill the 1 st and innermost energy shell. Because its outer energy shell is complete (in this case it is its only energy shell) then the atom and element are very stable or nonreactive. Its outer energy shell, which is the site where chemical reactions take place between elements, is full.

However, if the 3 rd energy shell (which can hold 18 electrons, but is happy with 8) has only 1 electron in it, it will naturally want to give up that 1 electron to another atom so that its next energy shell will be complete and make the element stable. On the other hand, if the 3 rd energy shell has 7 electrons, it will want to gain an electron to make up the 8 and become chemically stable. In chemistry, the easiest route to obtain the ‘desired result’ will always be taken. The ‘desired result’ is always stability and a state of equilibrium.

This is generally referred to as the ‘octet rule’.

The octet rule says: ‘atoms with fewer or more than 8 electrons in the outer energy level will attempt to lose, gain or share electrons with other atoms to achieve stability’

When an atom loses or gains an electron it ‘throws’ the electrical balance of the atom out, so it acquires a slight negative or positive charge overall.

Charge is another one of these terms that label a mysterious but predictable phenomena – we could have called it Velcro and talk about loops and hooks rather than positive and negative – it is no more meaningful. We have a phenomenon where tiny particles seem to attract each other – and so we give it an impressive name change and classify the extremes as positive and negative.

What gives us the electricity from our mains or from a battery is the flow of electrons from an area with a lot of electrons (= a lot of negative) to an area with a lot of protons (= a lot of positive) – from the negative end of a battery to the positive. Electric current is the term given to this flow of electrons.

What is happening here is nature's attempt to neutralise any extremes, just like hot and cold water mix in a bath to give an average temperature.

This difference of positive and negative is measured as voltage: a big voltage equals a big difference of positive & negative.

The important thing to understand is that an area of negative charge will always try to go to an area of positive charge, and vice versa.


Imagine you have 11 positive protons and 11 negative electrons: 11+ and 11 will cancel each other out, and so the atom is electrically neutral. But because there are 11 electrons, the energy shells will be filled with 2 in the first, 8 in the 2 nd and l in the 3 rd . This will mean that it is slightly reactive as an atom, and will want to lose that outer electron. When it gives up that electron to another atom that needs to gain l electron, it will effectively have 11 positive protons, but 10 negative electrons. There is now l more proton than electron, so the atom has a slight positive charge. If it had gained an electron, it would have l more negative electron than protons, and so would acquire a slight negative charge. They have both become ions: ‘ion’ means ‘going’ and this is really apt. Because of the slight charge they have acquired through gaining or losing electrons, the atoms are now pulled towards opposite charges: they are literally ‘going’ somewhere.

This is the basis of our first chemical bonding, the chemical joining of atoms to form molecules and other substances. An atom that has gained that extra negative electron, has become a negative ion, or an ‘anion’ (‘an’ means ‘negative’). The anion is attracted towards atoms that have lost a negative electron, and thereby become positive ions, or cations (‘cat’ means ‘positive’). So, rather like the movement when iron filings are attracted toward a magnet, positive cations and negative anions hurtle towards each other, pulled by their equal but opposite charges. (Remember: CATions are PURRSative.)

For example, an atom that has lost one electron is said to have a positive charge of l, written as + . An atom that has lost 2 electrons will have a positive charge of 2, written as ++ or 2 + . With the gaining of negative electrons, that charge becomes ¯ or ¯ ¯ .

Opposites attract, so an atom with a charge of + will attract an atom with a charge of ¯ . However, an atom with a charge of ++ can attract both an atom with a ¯ ¯ charge or 2 atoms with a single ¯ .

The common ions in physiology, and their charges are as follows: Positive (Cations). Negative (Anions). Name Symbol Charge ( + ) Name Symbol Charge ( )

Sodium Na + 1 Fluoride F 1

Potassium K + 1 Chloride Cl 1

Magnesium Mg 2+ 2 Oxygen O 2 2

Calcium Ca 2+ 2 Sulphate (S04) 2 2

Hydrogen H + 1 Nitrate (NO3) 1

Phosphate (PO4) 3 3

Bicarbonate (HCO3) 1 (or Hydrogen carbonate)


The elements can be roughly classed as: a) Metals (such as Iron, Sodium, Magnesium etc.),

and

b) NonMetals (Gases like Oxygen, Nitrogen, Hydrogen, Chlorine; solids like Carbon, Phosphorus).

Hydrogen is a half way house and though a gas acts a lot like a metal chemically.

The elements can be arranged in ascending order of the weight (mass) of the elements. This is the periodic table, by convention with metals on the left, non metals on the right.

(The ‘semiconductors’ we hear about are elements in the half way house position between metals and nonmetals with properties similar to both)

Metals form positive ions, nonmetals form negative ions.

Carbon is a nonmetal but it rarely forms ions by itself. It likes to form four bonds and so is excellent for making chains of molecules.

The numbers listed above give a clue to how elements will combine – like Lego bricks, they link together according to the number of charges. So oxygen forms 2 bonds, sodium just 1. With this information we would guess 2 sodiums would combine with 1 oxygen – and this indeed is what happens. This concept of the number of bonds an element forms is called its valency.

Ionic Bonds

Definition: formed by transferring electrons from one atom to another....

When these atoms finally join by equal but opposite attraction, we have created the first chemical joining, called a bond. Because these atoms are both ions, what we have is an ionic bond. Common table salt, or sodium chloride, is an example of an ionic bond of sodium and chlorine. Let’s take a look at it in a bit more detail. Sodium (Na) has an atomic number of 11, so there are 11 protons in the nucleus and 11 electrons in the energy shells, 2 fill the first, 8 fill the 2 nd , leaving l in the 3 rd . So sodium will want to lose that l electron to another atom, thus becoming a cation (+). Chlorine (Cl), on the other hand, has an atomic number of l7 and so has l7 protons and l7 electrons. Of these, 2 will fill the 1st shell, 8 the next shell and 7 will occupy the 3 rd . So chlorine will want to gain l electron to make that magic stable number of 8.


Sodium willingly donates its ‘spare’ electron and becomes a sodium cation, written as Na + and of course Chlorine gladly accepts the sodium electron and becomes a chlorine anion, or chloride, written as Cl . The 2 are equally opposite in electrical charge through the swapping of electrons and now ionically bond to form sodium chloride (NaCl). Their charges have cancelled each other out, leaving a very stable compound.

Covalent Bonds

Definition: chemical bond formed by two atoms sharing one or more pairs of electrons.....

Remember that, once you reach the 2 nd energy shell, 8 becomes the magic stable number of electrons to have in the reactive outer shell of that atom.

As long as the atom has only 2, or maybe 3 electrons to lose or gain, then ionic bonds will be the preference. However, carbon (atomic number 6) has 4 electrons in the outer shell and this makes it very unstable and reactive. It does not want to give up those 4 electrons, nor to gain 4 for that matter, so it compromises and shares them.

This type of chemical bonding is very significant in physiology. Carbon, oxygen, hydrogen and nitrogen are the major elements of the body and they almost always share electrons to form covalent bonds.

Covalent bonds that bind atoms together by sharing two pairs of electrons are called ‘double covalent bonds’ or double bonds. For example, a molecule of carbon dioxide results from two atoms of oxygen sharing two electrons with a carbon atom, they complete the outer energy field of 8 electrons and this satisfies the octet rule.

Hydrogen Bonds

Definition of a hydrogen bond: occurs when two atoms associate with a hydrogen atom, for instance oxygen and nitrogen.....

Ionic and covalent bonds function to form molecules. A third type of chemical bond can exist within or between molecules and is much weaker than the other two types of bond. These weaker bonds between molecules are called hydrogen bonds and are formed from an unequal charge distribution on a molecule (rather than forming chemical bonds from sharing electrons).

Hydrogen bonds are crucial for the formation of water (accounting for many of the unique properties of water and making it an ideal medium for the chemistry of life). They also play a significant role in maintaining the 3 dimensional structure of proteins and nucleic acids.


Chemical reactions

Interactions between atoms and molecules that involve the formation or breaking down of chemical bonds involves ‘chemical reactions’. During your study of physiology, you will become across 4 main chemical reactions that you should familiarise yourself with. These are:

1) Synthesis reaction (anabolism) combining two or more substances to form a more complex substance, for example, A+B = AB

2) Decomposition reaction (catabolism) involves substances decomposing or breaking down into two or more simpler substances, leading to the breaking of a chemical bond, for example, AB = A+B

3) Exchange reaction this reaction involves both of the above in creating new complex substances. The exchange reaction occurs when two complex substances decompose into simpler substances and these simpler substances then join with different simple substances to form new complex substances, for example, AB + CD (is broken down into) = A + B + C + D (then synthesised into) = AD + BC

4) Reversible reaction this reaction may require special conditions such as heat or light and many of the above chemical reactions are reversible.

Strangely, this is often the most feared part of chemistry, yet these symbols were designed to make the longhand descriptions of a reaction less of a chore.

The basic thing to grasp is that these shorthand sentences represent the BEFORE and AFTER situations. The symbol that divides ‘before’ from ‘after’ is the arrow ‘→‘.

The other symbols used are the symbols for the chemical element, the state the element is in (in water: (aq), as a gas: (g), as a liquid: (l) as a solid: (s).)

Finally, numbers are used to describe the elements properties or quantities. Three kinds of numbers are seen:

i) Ion numbers: we've seen these before: these are the numbers to the top right of the element's symbol (e.g.: Ca 2+ ,O 2 ). They indicate the number of positive or negative charges on the ion. By convention a single + or – is taken to mean 1+ or 1– .

ii) Molecule numbers: these are the small numbers found to the lower right of the element symbol. These represent the number of that particular element in that molecule (e.g. Water: H2O: there are two hydrogens here and one oxygen (the convention is not to put a 1 against the oxygen), Glucose: C6H12O6: there are six carbons, twelve hydrogens, six oxygens). The order the elements are listed is by convention – we tend to put carbons first, hydrogens second, oxygens third.


iii) Proportion numbers. These numbers are found to the left of symbol for the molecule or element. This indicates the number of molecules or atoms needed to make the equation's proportions balance.

(E.g.: 6C: six separate carbon atoms, 2H2: 2 separate hydrogen molecules, 2H2O: two separate water molecules.)

For example: When hydrogen and oxygen react to make water the chemical symbols would go as follows:

(Long hand) Hydrogen + Oxygen reacts to form water or Hydrogen oxide.

(Short hand) H2 + O2 → H2O

but we can see that there is an imbalance in the number of oxygens: on the left (one oxygen molecule O2 = two oxygen atoms) and right (one oxygen in the water molecule: H2O = one oxygen atom). To understand the true proportions in a reaction, the numbers of atoms on either sides of the equation must balance. To do this we want to use whole numbers (we could say ½O2 but this is clumsy) and this means increasing the number of hydrogen molecules: 2H2 + O2 → 2H2O

NB: The arrow → represents the fact that a chemical reaction has occurred: the ‘before’ being uncombined oxygen and hydrogen, the ‘after’ being water. When reactions can occur in both direction a double arrow ‘↔‘ is used to represent this reversible reaction.


Organic and Inorganic Compounds

The major difference between organic and inorganic compounds is that organic compounds generally contain carbon and carbonhydrogen bonds while inorganic compounds generally do not, and they never have CC (carboncarbon bonds) or CH (carbon hydrogen bonds). The human body has inorganic and organic compounds because both are equally important to the chemistry of life. We shall explore inorganic compounds first then go onto to look at organic compounds. Once you have a basic level of knowledge around this subject, please be sure to refer to your A&P book to enhance your understanding as it is crucial to you for your future confidence around biochemistry.

Inorganic Compounds

Inorganic compounds are generally small and include water, oxygen, carbon dioxide and electrolytes.

Water is the most abundant substance of the body and crucial to our survival. It makes up almost 70% of the total body weight and it is vital in all aspects regarding the chemistry of life including:

§ Polarity: because water easily forms polar covalent bonds, it permits the transport of solvents, and because many kinds of molecules can dissolve in cells, it permits a variety of chemical reactions that allows many substances to be transported throughout the body.

§ High specific heat: by both absorbing and releasing heat slowly, water enables the body to maintain a relatively constant temperature (with little change in its own temperature)

§ Lubrication: water acts as a lubricant in mucous and other body fluids that helps to cushion and protect against damage from trauma or friction.

Oxygen and carbon dioxide are very closely related to cellular respiration (which we will discuss more fully later in this booklet). Oxygen is required to complete the decomposition chemical reactions that are needed to release energy from nutrients burned by the cell. Carbon dioxide is produced as a waste product as a result of breaking down complex nutrients by the body and is also very important in maintaining the appropriate acidbase balance of the body.

The term Electrolytes is derived from ‘electro’, which means ‘electric charge’, and ‘lytes’ which means ‘can be dissolved in’. They can be dissolved in water, giving water the property of being able to conduct, or transport, an electrical charge.


Electrolytes are defined as ‘a substance that ionizes in solution, rendering the solution capable of conducting an electric current’. Acids, bases and salts are all electrolytes, or quite simply, compounds whose molecules contain ions that are positively charged (cations) and negatively charged (anions) these ionize, or separate into ions, in solution. The number of hydrogen ions the substance releases in solution, will determine how acidic that solution becomes. So, the level of acidity will depend on the number of hydrogen ions a particular acid will release. Conversely, the more hydroxide ions a solution contains, the more basic, or alkaline, it becomes. Salts form a compound when acids react with bases, they are classed as electrolytes and dissociate in solution to form positively and negatively charged ions. If the water element of the solution is removed, the ions will crystallise and form salt. These inorganic salts, dissociate in body fluids contributing important electrolytes that are crucial for numerous body functions such as proper nerve and muscle function, and they also play a vital role in fluid balance and therefore directly impact the homeostasis of the entire body.

So, you can appreciate that in a body that is 70% water, where transport of electrical impulses is vital for communication, the properties of electrolytes are extremely important. Electrolytes are in fact essential to cell physiology.

In brief then, § Electrolytes comprise of acids, bases and salts.

§ An acid is a compound that will always give up a hydrogen atom when dissolved, or broken apart, by water.

§ A base compound, when dissolved, will always accept a hydrogen atom.

§ A salt is an acid neutralized by its specific opposite base: during this process of forming the salt, some water is left over.

Some common salts used by the body would be:

NaCl Sodium Chloride (common table salt)

KCl Potassium Chloride

NaHCO3 Sodium Bicarbonate (commonly used as an antacid)

MgSO4 Magnesium Sulphate (good old Epsom Salts)

CaSO4 Calcium Sulphate (plaster of Paris)


Organic Compounds

Organic compounds commonly contain CC or CH bonds (carbon carbon or carbon hydrogen bonds). Because carbon atoms have 4 electons in their outer energy shell, they require another 4 electrons to satisfy the ‘octet rule’. This means that one carbon atom can join with 4 other atoms, giving it the ability to form thousands of different sized and shaped molecules! Carbohydrates, proteins, lipids and nucleic acids are the 4 major groups of organic substances in the human body. These macromolecules will be discussed in more detail in your nutrition lecture booklets and in your Thibodeau & Patton text book, so suffice to say for our purpose of understanding here, that they are composed of basic building blocks (for example glucose or amino acids), that are joined in chains by covalent bonds. This simply means that they can form 3 dimensional structures and provide the body with the means to produce and store energy, act as an aid to transportation, code and decode hereditary information, synthesise hormones and enzymes and provide structure and support to cells and tissues. This list is by no means exhaustive, as you will discover as you learn more about these super macromolecules.

All that I have just discussed is basic but essential chemistry. You need it to be able to understand the chemical reactions that take place in the body.

Our recommended A&P textbook, Thibodeau & Patton, has an excellent section on this subject, with diagrams to give you a sense of what is really happening. Please read this section as many times as you may need, until you find it enjoyable reading. When you do, you will know that your understanding of this subject is more complete. When you have become more familiar with chemical reactions you will be able to move on to the next part of the lecture, which discusses how nutrients, chemicals, and waste materials move in and out of the cell. If you still feel at all uncomfortable with the last part, then you could take a break, and when you feel ready, reread it until you can answer these questions below with reasonable confidence, referring to your A&P textbook for support.

We move back to the cell now. You may still be wondering why basic chemistry, and a knowledge of atoms, is necessary. Well, in the next two sections we will see how chemicals are brought into the cell, and how they are used to aid cell respiration. That is one of the most important processes to understand because the cell, and therefore the body, relies upon it for life. Cell respiration is an incredible complex series of chemical reactions which most A&P students never quite grasp because they have usually neglected their chemistry, for whatever reasons!!. Before we leave chemistry, have a quick look at the summary for this section.


Summary We are building a very nice foundation to your knowledge by dealing with the smallest units of matter we need to look at in A&P. We shall recap quickly before we move on to the next part of the lecture.

§ First there are atoms, the smallest parts of elements. § Atoms have three parts, protons, neutrons and electrons. § Protons are positively charged, electrons are negatively charged and

neutrons are neutral, no charge. § Protons and neutrons share the nucleus, while electrons orbit the nucleus like

a cloud of energy. § Electrons fill different orbits called energy shells in the order of 2, 8, 18 and 32.

After the 2 nd energy shell, 8 electrons will make that atom stable. The outer energy shell of an atom is the reactive part of an atom. If there are not 8 electrons in the outer shell the atom will lose or gain electrons with other atoms to make up that 8.

§ When an atom loses or gains an electron it acquires a negative or positive charge and is becomes an ion. Positive ions are cations, negative ions are anions.

§ Anions attract cations and bond ionically to become stable. Ionic bonds can be broken in water, releasing the ions and making the water able to conduct electricity. These ionically bonded molecules are therefore called electrolytes.

§ Acids, bases and salts are all electrolytes and are all vital to the body and cells’ survival.

§ Acids, when dissolved in water, always give off a hydrogen atom. Bases, when dissolved in water, always gain a hydrogen atom.

§ When an acid combines with its opposite base, they neutralize each other out, and produce a salt and some water.

§ Covalent bonds occur where two or more electrons are shared between atoms to form very strong and stable molecules. Each element has an electronegative charge that maintains the electrons orbit around the nucleus. If, when elements covalently bond, one element’s electronegative pull is greater than the other’s, then a polar covalent molecule is formed. Otherwise, the bond is a nonpolar covalent one. These polarended molecules attract very weak hydrogen atoms that bond forming a very weak hydrogen bond, which helps bind polar covalent molecules together and form 3D compounds, such as proteins and water.

§ Water is the universal polar covalent molecule.


B MOVEMENT IN AND OUT OF THE CELL

In order to survive, the body needs air (oxygen), water and food. As you already know, these materials are transported to the cells, via the blood and blood vessels.

Food is mechanically and chemically broken down until it is small enough to be absorbed, largely through the small intestine, into the blood/lymphatic system. The blood transports the nutrients, which are now in the form of proteins, lipids and carbohydrates, to the liver.

The liver breaks them down further and at the same time alters them so that they are now seen as friendly to the body and not alien to it. This prevents the immune system from attacking and destroying them. The liver passes the nutrients back into the general systemic circulation and the nutrients are ‘delivered’ around the body into the interstitial fluid that bathes and surrounds all cells.

The problem that arises now is how to transport the desired nutrients into the cell and how to collect and transport the waste and products of the cell out again, without letting undesirable substances in or out. Obviously a transport system for the cell is needed. There are two main types of transport systems: the passive transport systems, which require no energy from the cell in order to move substances in or out, and the active transport systems, which does require energy from the cell to fulfil the same functions.

PASSIVE TRANSPORT SYSTEMS

Let’s take a look at the passive transport systems first.

Passive transport works on a very simple principle that substances will always want to move from a high concentration to a low concentration until the two concentrations are equal.

Imagine a ball at the top of a slide. When the ball starts to roll down the slide, it will keep rolling until it reaches level ground and runs out of steam. It is here that the forces trying to move the ball equal those trying to stop it, whereas at the top of the slide, the downhill gradient was pulling it. Therefore, the ball will always move down the slide until it reaches level ground and never up it.

The same principle is found to operate in passive transport, but instead of a slide we have a concentration gradient. Substances that are more concentrated in one area (for example, nutrients outside the cell) will naturally move down the concentration gradient to where there is a lesser concentration of that substance (for example inside the cell) until the outside concentration and the inside concentration are equal


Therefore a passive transport system will always move water or substances down a concentration gradient. There are five types of passive transport system that all work on this natural law of ‘from a high concentration to a low concentration’ – these are Simple diffusion, Dialysis, Osmosis, Facilitated diffusion and Filtration

1. Simple diffusion

Diffusion is defined in the dictionary as "to spread out". We see this when a drop of ink is placed in clear water. The longer it’s left, the more diffuse the ink becomes until there is a uniform spread of ink in the water. The ink has diffused from the high concentration in the drop, to the lower concentration in the water. The ink is said to have moved down a concentration gradient: from a high concentration to a low concentration.

When molecules are in solution, i.e. dissolved, they tend to be bouncing around quite chaotically, colliding with other things as well as with each other. It is this energy that is used to move the molecules down the concentration gradient to an area of lower concentration.

For our purposes we define diffusion as the movement of a substance from a high concentration to a lower concentration. It occurs in gases and liquids.

Throughout the course of your study you will meet the following 3 important definitions: Solvent: liquid that can dissolve a substance: e.g. water.

Solute: a substance dissolved by a solvent: e.g. salt dissolved in water.

Solution: the combination of solvent and solute

We will use solute as it is a simple way to say "substances dissolved in water" but to save confusion we will talk about water not solvents.

In the body diffusion occurs across cell membranes as well through areas of liquid. Oxygen in the air diffuses into the cells of the alveoli (the tiny air sacs in the lungs) and then on into the blood. We shall see how the way the membrane is made can change the way diffusion occurs.


When the concentrations on either side of the membrane are equal equilibrium has occurred. It takes a certain amount of time to reach equilibrium and different situations will make equilibrium happen more slowly or quickly. At equilibrium, as many molecules are moving across the membrane in one direction as are going in the other so there is no net change in concentration either side of the membrane.

For rapid diffusion a large surface area, thin membrane and high concentration gradient is required. In addition, larger holes in the membrane, smaller molecules and, in the case of gases, having a moist membrane also aids diffusion.

Equilibrium in the lungs is reached amazingly rapidly in the lungs: within about 0.2 seconds of new air entering the alveoli.

Note: When considering diffusion for a number of gases across the same membrane each gas is considered SEPARATELY. They do not significantly interfere with each other, even if diffusing across the membrane in opposite directions.

Simple diffusion takes place either directly through the phospholipid cell membrane or through the protein channels embedded in the membrane. The molecules will move from a high concentration through the cell membrane to a low concentration until the concentrations are equal. At the same time, substances which are now high in concentration will be moving out of the cell, through the membranes into the extracellular fluid which has a low concentration of that substance.

Before moving on to look at dialysis have a look at the study exercise overleaf to guage your understanding at this point.


Ο Study Exercises The following diagrams indicate a container across which is a selectivelypermeable membrane. The dots either side of this membrane represent molecules, caught frozen for a split second as they madly rush around. In box A show with an arrow in which direction diffusion would occur across the membrane. In box B show in which direction the two types of gas molecule would move by diffusion.

Box A Box B

Ο Study Exercise Compare the pairs of diagrams below. In which box of each pair would diffusion across the membrane be most rapid/effective?

Pair 1

Pair 2

Permeable membrane with pores

A pore


Pair 3: In which example would most gas diffuse across before equilibrium?

Ο Study Exercise Diffusion continues until equilibrium is reached. Define "equilibrium". What are the features of a cell membrane that allow the maximum amount of diffusion to occur across it?

2. Dialysis.

You have probably heard of kidney dialysis machines, which work on the same principle as this passive transport system. We have a solvent, such as water, containing solutes, such as glucose and protein molecules. The protein molecules are larger than the water and glucose molecules. We have a selectively permeable membrane, which is a membrane that has pores in it large enough to allow the water and glucose molecules to pass through, but too small to allow the larger protein molecules to do so.

The membrane separates areas of a high concentration of glucose and protein from a low concentration of these substances. Now, because we already know that substances move from a high to a low concentration, we can appreciate how it is that the glucose molecules pass through the semipermeable membrane into the lower concentration of glucose molecules. At the same time, water, which is the solvent, will be in a greater concentration on the side of lower glucose concentration, and so as glucose moves one way, water moves the other way, down its concentration gradient. What we have then is a double movement until the glucose/water concentrations are equal. The protein molecules cannot fit through the pores so they remain at the same concentrations.


3. Osmosis

Is our next passive transport movement, and refers to the diffusion of water through a semipermeable (or selectively permeable) membrane, from a high concentration of water (which will equal a low concentration of the solute dissolved in it) to a low concentration of water (which will equal a high concentration of solute dissolved in it).

This kind of movement occurs frequently in a body that is 70% water and is vital in maintaining homeostasis, that state of relative equilibrium within a body necessary to maintain life. In moving, the water will transport many dissolved substances as long as the semipermeable membrane’s pores are large enough for them to pass through.

The amount of solute dissolved in water governs the strength of that solution. Thus if we dissolve some salt in water we can make solutions of varying strengths. The more salt we put in the stronger the solution and the less water there is in the solution (the solute is displacing the water). The diagrams below indicate the proportions in different mixes.

25% Salt 50% Salt 75% Salt 100%

Water 75%

Water 50%

Water 25%

Water

100% Salt

100% Water

75% Water

50% Water

25% Water

0% Water

0% Salt 25% Salt 50% Salt 75% Salt 100% Salt

Becoming more hypERtonic relative to the containers on left, direction water

would move by osmosis between containers.

Becoming more hypOtonic relative to the containers on right.


As we can see, the more solute the stronger the solution the 50% solution is stronger than the 25% solution and yet weaker than the 75% solution. When we compare 2 solutions of different concentration we call the stronger of the pair hypertonic and the weaker one hypotonic. If they have the same concentration the solutions are isotonic.

Thus, a hypertonic solution has less water so can be said to contain a lower concentration of water and a hypotonic solution has more water so can be said to contain a higher concentration of water.

NOTE: When we consider body fluids they contain many solutes. The strength of a solution depends on the total number of dissolved solute particles and not on the type of solute particle. So that a 10% glucose solution is isotonic when compared to a solution that contains 5% sucrose and 5% fructose.

When we consider the fluids in and out of cells, differences in concentration have dramatic effects. The fluid on the outside of cells is called extracellular fluid (ECF) The fluid on the inside of cells is called intracellular fluid (ICF) The circles below represent cells (which all have the same initial ICF concentration) placed in solutions of different concentrations and the effects that occur after time has elapsed.

Initial situations:

Final situations:

ICF hypotonic

ECF hypertonic

Cell shrinks

ICF isotonic with

ECF

No change

ICF hypertonic

ECF hypotonic

Cell bursts

Ο Study Exercise On the diagram of cells above, draw the direction that the water is moving across the cell membranes in each case, using arrows.


Why do these effects occur? They occur when the membrane does not allow the movement of solute molecules across the membrane but DOES allow water to move. Water moves by diffusion from where it is in high concentration (a hypotonic solution) to where it is in low concentration (a hypertonic solution). The water continues to move across the membrane until equilibrium occurs and the solutions are isotonic with each other.

The size of the holes in the membrane are central to this effect. § If they are so small that no water or solute passes through the

membrane is impermeable.

§ If the size allows water through but NOT the solute the membrane is selectivelypermeable (sometimes called semipermeable). In the body, the cell membrane contains protein channels that are selective for certain solutes. Some of these are “gated” – they can be opened or closed according to circumstance. The active transport pumps in cell membranes also act as selective barriers, pumping in one direction across the membrane and not the other.

§ If the size allows water AND solute through the membrane is (fully) permeable.

In the body most membranes are selectivelypermeable membranes (a SPM).

The special type of diffusion by water across SPMs is called osmosis. This can be defined as the movement of water from a high concentration of water to a low concentration of water across a selectivelypermeable membrane until equilibrium is achieved. There is no net movement of water across the membrane when equilibrium has been achieved.

However, substituting hypertonic and hypotonic can make this clearer: Osmosis is the movement of water from a hypotonic solution to a hypertonic solution across a selectivelypermeable membrane until equilibrium is achieved.

Key point In the body, water moves across cell membranes by osmosis.


When solutes are actively pumped from one side of a cell membrane to another, the change in relative concentration sets up an osmotic gradient that will result in water “following” the pumped solute. Thus when isotonic sports drinks are consumed, solutes in the drink are actively pumped across the intestinal membranes and the water follows passively.

The movement of water across the membrane exerts a pressure and we call this the osmotic pressure, which is exerted towards the hypertonic solution, however when the solute involved is protein as in the case of plasma protein in capillaries, the osmotic pressure that is generated is sometimes referred to as oncotic pressure. The osmotic pressure is what burst the cell in the above examples. This risk of bursting cells is why intravenous fluids (fluids given via a vein, commonly known as a “drip”) are usually isotonic. In medicine the word normal is often used instead of isotonic: thus normal saline just means an isotonic saline solution that has the same concentration as blood.

One of the signs of a toxic cell, and hence of a toxic person, is that when water rushes into the cell to try and create equilibrium, the cell bloats and hence the person bloats. You can see that an understanding of these basic processes in a healthy cell will help you to understand what is happening in a diseased state.

4. Facilitated diffusion

This may seem to imply that activity is required for it to take place, but in fact this passive transport system refers to the use of a protein channel through the phospholipid membrane to ‘facilitate’ movement into, or out of, the cell. Again, the molecules move down the concentration gradient from high to low, but in facilitated diffusion a specific molecule uses a specifically shaped protein channel to aid its journey.

5. Filtration

Finally, we have filtration a process used extensively by the blood vessels and the kidneys. Imagine a long hose pipe with thousands of tiny holes perforating it. Inside the hose there is a solution of water, glucose and very large protein molecules, too big to pass through the tiny holes in the hose. The hose is full, but no water comes out of those tiny holes. However, when the hose has more of that solution pumped through it, the water and glucose begin to spray out of the holes, leaving the large protein molecules and some water behind.


What has changed here? The pressure. Just as we can have a concentration gradient, we can also have a hydrostatic pressure gradient. The hydrostatic pressure inside the hose rapidly builds up when the solution is pumped through. Because the hydrostatic pressure outside the hose is much less, the water and glucose solution are able to filtrate out of the hose, whereas the protein solution is too big to do so, despite the pressure. The result (if the hose was long enough) would be that you would eventually be left with a pure protein solution inside the hose and a pure glucose solution outside. Filtration would be said to have occurred.

The ever narrowing blood vessels, together with the mechanical pressure provided by the heart and other mechanisms, create an increasingly higher hydrostatic pressure which allows substances such as glucose to filter out into the interstitial fluids. The kidneys also use this process extensively, to extract any useful materials from the blood while leaving the toxic, or unwanted, larger materials to be collected and excreted as urine.

Summary Let’s summarise that section. Passive transport systems always work on the principle and law of ‘from a high concentration to a low concentration’. Simple diffusion is the movement of molecules through a membrane from high to low concentration. Dialysis is the movement of small enough molecules through a semipermeable (or selectively permeable) membrane from high to low concentration. Osmosis is the movement of water through a selectivelypermeable membrane from high to low concentration. Facilitated diffusion is the movement of specific molecules through membranes via a protein channel specific to the molecule. Filtration is the movement of water and small enough molecules though a semi permeable membrane, under the influence of hydrostatic pressure, from a high to a low concentration.


ACTIVE TRANSPORT SYSTEMS

Passive transport is very valuable to the cell, but if an area of cells desperately needs an exchange of materials, or if a cell needs to pass materials up the concentration gradient (i.e. up hill’) then an active transport system is crucial.

Active transport is the complete opposite of passive transport in as much as it moves molecules up the concentration gradient with the aid of energy from the cell. There are three types of active transport that work on this principle.

Membrane Pumps

One of the most important active transport systems is the sodium/potassium pump.

It is absolutely vital that, as a wholistic nutritionist, you have a clear understanding of this system. You will not generally find this part explained in text books, but sodium’s natural place is outside the cell while potassium’s rightful place is inside it.

During the day, sodium (along with other substances) moves into the cell, displacing potassium, and the cell slowly becomes toxic bringing a feeling of tiredness. During the night, potassium moves back into the cell and sodium is pumped out again, and so we have this continuing cycle to restore the natural, healthy balance.

The way this natural exchange takes place is very simple. Sodium has lost an electron and so has become a cation (Na + ) with a positive charge. On the inside of the cell membrane, a carrier protein channel specific to sodium/potassium transport, provides a very specific binding point for the sodium cations. Sodium moves in and out in threes and so, when the sodium binding point recognises contact, it allows itself to accept an energy rich ATP molecule (like a battery being placed into a tape machine) in order to acquire the energy required for transport. The channel moves the three sodium cations through and then releases them into the cell.

As it releases the sodium cations, the protein channel attracts two potassium cations (K + ) to a specific potassium binding spot and reverses the process to expel the potassium into the extracellular fluid. The ATP molecule (more about this later), which gave some of its stored energy by having one of its phosphate bonds broken, is released back into the cell as ADP and sets off to be rejoined with its lost phosphate molecule and become energy rich ATP again.


It is the chemical ‘breaking’ of one phosphate atom from the ATP that releases the abundance of energy, which was previously being used to hold on to the phosphorous atom. This is pretty much like a Christmas cracker being pulled: the ‘crack’ is the energy being released.

With every 3 sodium ions moving in, 2 potassium ions are lost and vice versa, when the process is reversed. This is a very important point to remember and will become extremely relevant later on in the course.

There are many similar pumps, such as the calcium pump in the muscles’ cells, but none as vital to health as the sodium/potassium pump.

Other types of active transport mechanisms are endocytosis and exocytosis. These two mechanisms, although requiring expenditure of energy by the cell, will not, as the previous pump mechanism, allow for substances to move through the cell’s plasma membrane.

Endocytosis

Endocytosis means ‘process that brings into the cell’. There are two basic types of endocytosis. One is phagocytosis (‘phago’ means to eat, ‘cyto’ appertains to the cell and ‘osis’ means process, hence ‘process of the cell that eats’). This process is concerned with engulfing large particles such as bacteria, microorganisms and dead cells within the plasma membrane and bringing them into the cell by means of vesicle. Enzymes will ‘digest’ the substances and diffuse them.

Pinocytosis

meaning ‘process of the cell that drinks’, is a similar process that deals with engulfing fluids with dissolved particles, and letting them into a cell.

Exocytosis

Exocytosis means ‘process that releases from the cell’, and that is what it does. This process allows large molecules, such as proteins, to leave the cell without them having to pass through the cell’s membrane. Once again, vesicles are involved in the process of transportation, this time on the way out. Exocytosis is also responsible for the renewal of the plasma membrane, by allowing new membrane material to be laid down.


C : INSIDE THE CELL CELL RESPIRATION

Now that we have had a look at the components of elements, atoms and how they react, as well as how the body and cell transport materials in and out, let’s look at what the cell does with these materials.

There are two basic processes that can happen. Either these molecules or substances can be broken down further, or they can be used to build something else. Now we will study the most important cellular process involved in breaking down these materials further. This ‘breaking’ pathway is known as a catabolic pathway (‘catabolic’ means ‘to break down’). The most important cellular catabolic pathway is a process that resides beneath the title of cellular respiration.

Cellular respiration is simply the process by which glucose (the simplest form of sugar in the body) is broken down, leaving carbon dioxide and water as end waste products.

So, if CO2 and water are the waste products from cellular respiration, what benefit does the cell receive from chemically breaking down glucose in the first place?

Do you remember those very strong bonds that I spoke about earlier? Well, the energy that is harnessed in those bonds is released when they are broken. When this happens, the main product is the heat which helps maintain the temperature required for life. But some of that released energy is used to aid other chemical reactions. Most importantly, that energy is put to use creating the energy store compound of the cell known as ATP.

ATP and High Energy Bonds

ATP, or adenosine triphosphate, is really two substances bonded together. Firstly we have a molecule of adenosine, which functions as a vehicle for the 3 (tri) phosphate molecules that are joined to it in a chain.

The bonds that join the phosphate molecules to each other are the key to why the body and cell use ATP as the energy rich source for most of its energy needs. The phosphate bonds are known as high energy bonds because (surprisingly!) that is exactly what they are. The bonds are written as the symbol ‘~’, e.g. ‘P~P’, symbolising that there is a high energy bond between these two phosphate molecules. When water is introduced, hydrolysis (or dissolving) begins, and like the Christmas cracker, one phosphate is pulled away from the other and a huge surge of energy is released. ADP, or adenosine diphosphate (with 2 phosphate molecules), and one phosphate molecule will be left floating around.


It is usual for the last phosphate molecule to be dissolved, leaving ADP and a phosphate, but ADP can also have its other phosphate high energy bond broken if the requirement is desperate. What is more usual is for the ADP molecule and phosphate molecule to totter off to reform as ATP again, by reentering the cellular respiration at some stage.

The whole series of chemical stages and cycles known as cellular respiration exist to produce this precious energy store compound, known as ATP. This system is so efficient that from just 1 molecule of glucose, 36 molecules of ATP can be produced. To produce these 36 molecules of ATP the glucose enters three specific stages. One stage takes place inside the cell’s cytosol, while the other two stages take place inside the organelle called the mitochondria or the cell’s power factory.

The three stages of cellular respiration are: glycolysis, the krebs cycle or citric acid cycle and the electron transport system.

Glycolysis

This term derives ‘glyco’ from glycogen (the body’s format for glucose) and ‘lysis’ which means ‘to break’, giving us ‘to break glucose or glycogen’. In fact, the first stage of cellular respiration is to break the glucose in half, forming two new molecules of pyruvic acid (but more about that later).

The breaking down of glucose takes place in the fluidy part of the cell, the cytosol. The process requires no oxygen (hence it is called anaerobic) and glucose is broken down by the interaction of specific enzymes in the cytosol. Nine different reactions take place, simply to split glucose in half, but this is a prerequisite for the next processes begin. During these nine reactions, 4 molecules of ATP are produced, however, in the process of breaking glucose, two molecules of ATP are used, so from those four we have a net total of two left.


Glycolosis Ctd…

If you look in your text book at the flow chart headed ‘GLYCOLYSIS’ and at the summary diagram below and then look at the top of the Figure and the bottom where there is the end result of pyruvic acid. The middle part gives you an idea of the direction that the chemical reactions take to reach an end result. Once glucose is split in half it becomes a new and different substance called pyruvic acid. Pyruvic acid, if you like, now has a choice. If oxygen is present it will take the aerobic (with oxygen present) pathway, which will then lead it into the next two stages described further on.

However, if oxygen is absent or below the requirements needed, it will continue on the anaerobic (without oxygen present) pathway to form a substance that most people have heard of lactic acid. Lactic acid is implicated in the context of the tired, achy muscles experienced by people who have just been very active. They say that they have lactic acid in their muscles, and indeed they have. Because there was not enough oxygen supplied to the muscle cells to produce further ATP for their activity, the glucose was converted to lactic acid, which is toxic and forces one to STOP using those muscles. Lactic acid is however, far less toxic than pyruvic acid – and so its formation offers a protection against the buildup of toxic pyruvic acid. Note that alternative names for lactic and pyruvic acid are lactate and pyruvate.

The lactic acid will diffuse out of the cell into the lesser concentrated extracellular fluid. From here it will continue into the blood, until it reaches the liver where it will be converted back into pyruvic acid. It will be used by other cells around the body that have enough oxygen to complete cellular respiration (see, nothing is wasted! Marvellous, don’t you think?)

Let’s continue now on the assumption that our glucose molecule has been successfully split in half and is now pyruvic acid, and that oxygen is abundant.

The next stage is for the pyruvic acid to pass into the ‘power factory’ of the cell, the mitochondria. As it passes into the mitochondria, it is changed once more into another very important substance, called Coenzyme A (usually written as CoA). It is now ready to enter stage two, the citric acid cycle otherwise known as the Krebs Cycle (after Hans Krebs, the chap who discovered this cycle).


The Krebs Cycle or Citric Acid Cycle

The Krebs cycle is a complex cycle of chemical reactions (which you do not have to remember, so wipe the perspiration from your brow!) that takes the broken glucose molecules and breaks them down further, forming new molecules of various substances that continue to be broken down further or combined. As these reactions pass twice around the cycle, several ATP molecules are produced.

The main purpose of the cycle is to split molecules up further, and to ‘grab’ the stored energy from their bonds to make ATP. As the molecules continue to break down, they release negatively charged, highly energised electrons (e ) and their accompanying energised hydrogen protons (H + ). There are special carrier molecules which pick up these electrons and hydrogen protons so that they are not wasted or left to float around causing havoc. The carrier molecules transport them to the next crucial stage of the production of ATP, the electron transport system.

THE ELECTRON TRANSPORT SYSTEM

To my mind, this is the cleverest of all the stages. Here, a kind of hydrodam is formed with the electrons being like the dammed up water. They are allowed through narrow gates and just as water pressure turns turbines to make electricity, the energy produced from rushing electrons is harnessed to produce ATP.

All this happens in the internal chambers of the mitochondria and highlights, I believe, Nature’s incomparable simplicity and desire to avoid any ‘waste’.

The electrons that had been separated in the Krebs cycle rush through the inner chambers of the mitochondria to the outer chambers, dragging with them the hydrogen protons (H + ).

A massive concentration of hydrogen protons is very quickly created in the outer chamber, and because of those ‘high to low’ concentration gradients we talked about earlier, this creates a great need for the protons to balance the difference between the inner and outer chambers. However, the only way back into the inner chamber is single file through a limited number of channels.

What we have then is this natural hydrodam with a great force of protons wanting to pass through these small channels in the mitochondria inner membranes so as to create equilibrium. As hydrogen protons flood through the portals, great energy is produced and this is harnessed to make up the greatest amount of ATP in the three stages of cellular respiration.


Please use the diagram below as a quick reference for aerobic and anaerobic respiration

Process

CELL (INTRACELLULAR FLUID)

Lactic Acid Into Blood

Oxygen from Lungs via Blood

CO2 into blood, to lungs

Most Heat Lost by Skin

WITH OXYGEN

SOME ATP (2)

BLOOD GLUCOSE POOL

GLUCOSE

GLYCOLYSIS IN CYTOPLASM

(1 MOLECULE OF GLUCOSE SPLIT INTO 2)

PRODUCTS OF GLYCOLYSIS: PYRUVATE

(also called Pyruvic Acid)

WITHOUT OXYGEN

Fatty Acids and Some Amino

Acids

Glycerol, Fatty Acids and Ketone

Bodies from Lipid Breakdown.

Some Amino Acids.

LOTS OF ATP (38)

CARBON DIOXIDE

DIET

WATER HEAT

Aerobic Respiration

IN THE MITOCHONDRIA

KREB'S CITRIC ACID CYCLE

Acetyl CoA

LACTIC ACID

Anaerobic Respiration

With Insulin

LIVER CONVERTS THESE TO GLUCOSE BY

GLUCONEOGENESIS: Glycogen (stored glucose), Lipid (breaks down to Fatty Acids & Glycerol), Amino Acids (from Proteins) and Lactic Acid (also

called lactate)

BLOOD POOL OF: Fatty Acids, Glycerol &

Ketone Bodies (from lipids in fat stores), Amino Acids

(from proteins). Pool regulated by liver.

TISSUE FLUID BATHING CELL

AEROBIC & ANAEROBIC RESPIRATION

Terms Double Underlined are key ones to remember

© Tim Duerden2004


Summary Let’s once more summarise this final part of the lecture.

Glucose enters the cell and is split in half, forming pyruvic acid and two ATP molecules by a process called glycolysis.

Pyruvic acid, in the presence of oxygen, then enters the mitochondria and is changed to Coenzyme A (CoA). This passes through two complete turns of the Krebs Cycle or citric acid cycle, where it is further broken down. As energy is released from the breaking bonds, more ATP is produced. More importantly though, energised negatively charged electrons (e ) are released along with hydrogen protons (H + ) from the many reactions. These are picked up by specific carrier molecules and transported to the next stage of cellular respiration, the electron transport system. The electrons rush through the inner chamber and into the outer chamber, dragging the hydrogen protons with them. Very quickly, a kind of dam is formed with the protons needing to pass back into the inner chamber so as to restore equilibrium. As the protons, under great pressure, pass through the narrow channels, a great deal of energy is generated which is used to produce the majority of ATP, far more than is produced in the preceding 2 stages of cell respiration.

All this is vital to the life of the cell, and therefore of the person, as ATP provides 95% of the energy available for the vital functions of cell life.

CONCLUSION

This lecture along with the previous lectures that introduced you to the chemistry of nutrition and the cell have encompassed a great deal of material. You are not expected to remember it all at this stage, but if you re read it with the aid of the relevant chapters in your textbook, you will be able to flick through this one day as simple revision!

You will be finding that there is a strong link between these A&P lectures, and the ones in the Nutritional Healing and Nutrition modules. We think that this crosslinking is very important, bearing in mind that you will be using the information in a therapeutic context. I hope you have found this Session enjoyable.


THE FUNCTIONS OF THE CELL

Gas Exchange (Oxygen in CO 2 out)

Normal Metaboliic Processes (e.g. energy production)

Water Electrolytes (Minerals / Salts)

Atmospheric Pressure

Messages from

Adjacent or Distant Cells

Temperature pH

(Acid / Alkaline Balance)

Nutrients In Wastes Out

Normal Protein Synthesis

(requires normal genetic function)

Normal Intracellular Transport

Normal Cell Membrane (for transport in/out cell and receiving

messages)

Cell Manufactures Substance For Secretions

Building Blocks Absorbed by

Cell

Secretion Released into Blood, Tissue Fluid, Duct

Contraction of Contractile Fibres in

Cell

Stimulation of Cell Receptors

Movement of Cell or

Contraction of Muscle Cell

Cell Receptors Detect Stimulus and

Cell Responds

Stimulus (Chemical, Mechanical, Temperature, Light, Pain)

Response: (Secretion, Contraction, Altered

Metabolism etc)

Cell Undergoes Cell Division if it is Able

Loss of Contact from Adjacent Cells

or Other Stimuli

New Cells Produced

External Requirement

Internal Requirement

Normal Function

Processes Involved

KEY

This diagram offers a visual summary of key cell functions.


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ANATOMY & PHYSIOLOGY SERIES - nutrihealfoundation.com fileuntil we cut one open we would not know why they jump (the grub inside is responsible). But all we find if we ‘cut open’