Chapter 3 and 4 Nutrition, Culture and Enzymes

8/10/2019 Chapter 3 and 4 Nutrition, Culture and Enzymes

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Chapter 2 Journey to Microbial

World


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Chapter 4 Nutrition and Culture

of Microorganisms


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Different chemical reactions and organizemany different molecules into specific

structures is known as metabolism

Catabolism breaks molecular structures down,releasing energy in the process, and

anabolism uses energy to build larger

molecules from smaller ones.

Metabolic reactions are either catabolic,which means energy releasing, or anabolic,

which means energy requiring.


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All microbial nutrients are compoundsconstructed from the chemical elements.

However, just a handful of elements

dominate living systems and areessential: hydrogen (H), oxygen (O),

carbon (C), nitrogen (N), phosphorus

(P), sulfur (S), and selenium (Se). Inaddition to these, at least 50 other

elements, although not required, are

metabolized in some way by

microorganisms


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Besides water, which makes up 7080%of the wet weight of a microbial cell (a

single cell of Escherichia coli weighs just

g), cells consist primarily ofmacromoleculesproteins, nucleic

acids, lipids, and polysaccharides.


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A bacterial cell is about 13% nitrogen,which is present in proteins, nucleic

acids, and several other cell

constituents. The bulk of nitrogenavailable in nature is in inorganic form

as ammonia (NH3), nitrate, or nitrogen

gas (N2)


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Other Macronutrients: P, S, K,Mg,

Ca, Na

In addition to C, N, O, and H, many otherelements are needed by cells, but in smaller

amounts .

Phosphorus is a key element in nucleic acidsand phospholipids and is typically supplied to

a cell as phosphate (PO4)

Sulfur is present in the amino acids cysteine

and methionine and also in several vitamins,including thiamine, biotin, and lipoic acid.

Sulfur can be supplied to cells in several

forms, including sulfide (HS2) and sulfate

(SO4)


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Potassium (K) is required for the activityof several enzymes, whereasmagnesium

(Mg) functions to stabilize ribosomes,membranes, and nucleic acids and isalso required for the activity of manyenzymes.

Calcium (Ca) is not required by all cellsbut can play a role in helping to stabilizemicrobial cell walls, and it plays a keyrole in the heat stability of endospores.


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Sodium (Na) is required by some, but not all,microorganisms, and its requirement is

typically a reflection of the habitat. For

example,seawater contains relatively high

levels of Na, and marine

microorganisms typically require Na for

growth.

By contrast, freshwater species are usuallyable to grow in the absence of Na.

K, Mg, Ca, and Na are all supplied to cells as

salts, typically as chloride or sulfate salts.


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Micronutrients: Iron and Other

Trace Metals

Microorganisms require several metalsfor growth

Chief among these is iron (Fe), which

plays a major role in cellular respiration.Iron is a key component of cytochromes

and of ironsulfur proteins involved in

electron transport reactions . Under anoxic conditions, iron is

generally in the ferrous form and

soluble. However, under oxic conditions,


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Defined media are prepared by adding preciseamounts of highly purified inorganic or organic

chemicals to distilled water.

Therefore, the exact composition of a defined

medium (in both a qualitative and quantitativesense) is known.

Major importance in any culture medium is the

carbon source because all cells need large

amounts of carbon to make new cell material


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For culturing many microorganisms, knowledge ofthe exact

composition of a medium is not essential. In

these instances

complex media may suffice and may even be

advantageous.

Complex media employ digests of microbial,

animal or plant products, such as casein (milkprotein), beef (beef extract), soybeans (tryptic soy

broth), yeast cells (yeast extract), or any of a

number of other highly nutritious yet impure

substances.


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An enriched medium, often used for theculture of otherwise difficult-to-grow

nutritionally demanding (fastidious)

microorganisms, starts with a complexbase and is embellished with additional

nutrients such as serum, blood, or other

highly nutritious substances.


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A selective medium contains compounds thatinhibit the growth of some microorganisms but

not others. For example, media are available

for the selective isolation

of pathogenic strains of E. coli from food

products, such as ground beef, that could be

contaminated with this organism.


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Differential medium is one in which anindicator, typically a reactive dye, is

added that reveals whether a particular

chemical reaction has occurred duringgrowth.


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Solid and Liquid Culture Media

Liquid culture media are sometimessolidified by the addition of a gelling

agent.

Solid media immobilize cells,

allowing them to grow and form

visible, isolated masses called

colonies.


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Solid and Liquid Culture Media

Microbial colonies are of various shapesand sizes depending on the organism,

the culture conditions, the nutrient

supply, and several other physiologicalparameters, and can contain several

billion individual cells.

Some microorganisms producepigments that cause the colony to be

colored. Colonies permit the

microbiologist to visualize the

com osition and resum tive


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Solid media are prepared in the same way asliquid media

except that before sterilization, agar, a gelling

agent, is added to the medium, typically at a

concentration of 12%.

The agar melts during the sterilization process,

and the molten medium is then poured into sterile

glass or plastic plates and allowed to solidify

before use.


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ENERGY AND THE CELL

2012 Pearson Education, Inc.

Cells transform energy as they perform work


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Cells are small units, a chemicalfactory, housing thousands of

chemical reactions.

Cells use these chemical reactions

for

cell maintenance, manufacture of cellular parts,

and 2012 Pearson Education, Inc.



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Energyis the capacity to cause changeor to perform work.

There are two kinds of energy.

1.Kinetic energyis the energy ofmotion.

2.Potential energyis energy that

matter possesses as a result of its

location or structure.


Figure 5.10

Fuel Energy conversion Waste products


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Fuel Energy conversion p

Gasoline

Oxygen

Oxygen

Glucose

Heatenergy

Combustion

Kinetic energyof movement

Energy conversion in a car

Energy conversion in a cell

Energy for cellular work

Cellular respiration

ATP ATP

Heatenergy

Carbon dioxide

Carbon dioxide

Water

Water

Figure 5.10_1


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Gasoline

Oxygen

Heatenergy

Combustion

Kinetic energyof movement

Energy conversion in a car

Carbon dioxide

Water

Figure 5.10_2


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Oxygen

Glucose

Energy conversion in a cell

Energy for cellular work


ATP ATP

Heatenergy

Carbon dioxide

Water




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gy y p

Heat, or thermal energy, is a type ofkinetic energy associated with the

random movement of atoms or

molecules. Light is also a type of kinetic energy,

and can be harnessed to power

photosynthesis.




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gy y p

Chemical energy is the potentialenergy available for release in a

chemical reaction. It is the most

important type of energy for living

organisms to power the work of the

cell.



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C ll t f th f k


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Two laws govern energytransformations in organisms.

According to the

first law of thermodynamics,energy in the universe is constant,

and

second law of thermodynamics,energy conversions increase the

disorder of the universe.



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Chemical reactions either release or store


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energy

Chemical reactions either release energy (exergonic

reactions) or

require an input of energy and

store energy (endergonic

reactions).




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energy

Exergonic reactionsrelease energy. These reactions release the energy

in covalent bonds of the reactants.

Burning wood releases the energy inglucose as heat and light.


involves many steps,

releases energy slowly, and

uses some of the released energy to

roduce ATP. 2012 Pearson Education, Inc.

Figure 5.11A


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Reactants

Energy

Products

Amount of

energy

released

Potentialenergyofmolecules



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energy

An endergonic reaction requires an input of energy and

yields products rich in potential

energy.Endergonic reactions

begin with reactant molecules that

contain relatively little potential

energy but

end with products that contain more 2012 Pearson Education, Inc. Figure 5.11B


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Reactants

Energy

Products

Amount of

energyrequired

Potentialenergyofmol

ecules



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energy

Photosynthesis is a type of endergonicprocess.

Energy-poor reactants, carbon

dioxide, and water are used. Energy is absorbed from sunlight.

Energy-rich sugar molecules are

produced.




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energy

A living organism carries out thousands ofendergonic and exergonic chemical

reactions.

The total of an organisms chemicalreactions is called metabolism.

A metabolic pathwayis a series of

chemical reactions that either

builds a complex molecule or

breaks down a complex molecule into

simpler compounds. 2012 Pearson Education, Inc.



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energy

Energy coupling uses the energy released from exergonic

reactions to drive

essential endergonic reactions, usually using the energy stored in

ATP molecules.


ATP drives cellular work by coupling exergonic


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ATP,adenosine triphosphate, powers nearlyall forms of cellular work.

ATP consists of

the nitrogenous base adenine, the five-carbon sugar ribose, and

three phosphate groups.

and endergonic reactions



d d i ti


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Hydrolysis of ATP releases energy bytransferring its third phosphate from

ATP to some other molecule in a

process called phosphorylation.Most cellular work depends on ATP

energizing molecules by

phosphorylating them.


Figure 5.12A_s1 ATP: Adenosine Triphosphate


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Adenine

P P P

Phosphategroup

Ribose

Figure 5.12A_s2 ATP: Adenosine Triphosphate


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ADP: Adenosine Diphosphate

P P P Energy

H2OHydrolysis

Ribose

Adenine

P P P

Phosphategroup


d d i ti


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There are three main types ofcellular work:

1.chemical,

2.mechanical, and

3.transport.

ATP drives all three of these typesof work.


Figure 5.12B

Chemical work Mechanical work Transport work


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ATP ATP ATP

ADP ADP ADPP P P

P

P

P

PP

PReactants

Motorprotein

Solute

Membrane protein

Product

Molecule formed Protein filament moved Solute transported

ATP drives cellular work by coupling exergonicd d i ti


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ATP is a renewable source of energyfor the cell.

In the ATP cycle, energy released in an

exergonic reaction, such as thebreakdown of glucose,is used in an

endergonic reaction to generate ATP.


Figure 5.12C


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Energy fromexergonicreactions

Energy forendergonicreactions

ATP

ADP P


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HOW ENZYMES FUNCTION


Enzymes speed up the cells chemical reactions bylowering energy barriers


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lowering energy barriers

Although biological molecules possess muchpotential energy, it is not released

spontaneously.

An energy barrier must be overcome

before a chemical reaction can begin.

This energy is called the activation

energy(EA).


Enzymes speed up the cells chemical reactionsby lowering energy barriers


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by lowering energy barriers

We can think of EA as the amount of energy needed for a

reactant molecule to move uphill to a

higher energy but an unstable state

so that the downhill part of the reaction

can begin.

One way to speed up a reaction is to add

heat,

which agitates atoms so that bonds break

more easily and reactions can proceed

but 2012 Pearson Education, Inc.

Figure 5.13A


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Activation

energy barrier

Reactant

Products

Without enzyme With enzyme

Reactant

Products

Enzyme

Activation

energy

barrier

reduced by

enzyme

Energ

y

Energ

y

Figure 5.13A_1

Activation


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Activation

energy barrier

Reactant

Products

Without enzyme

Energy

Figure 5.13A_2


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Activation

energy

barrier

reduced by

enzymeReactant

Products

With enzyme

Energ

y

Enzyme

Figure 5.13Q


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Reactants

Products

Energy

Progress of the reaction

a

b

c

Enzymes speed up the cells chemical reactionsby lowering energy barriers


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by lowering energy barriers

Enzymes function as biological catalysts by

lowering the EAneeded for a reaction

to begin, increase the rate of a reaction

without being consumed by the

reaction, and are usually proteins, although some

RNA molecules can function as 2012 Pearson Education, Inc.


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Animation: How Enzymes WorkRight click on animation / Click play

A specific enzyme catalyzes each cellularreaction


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reaction

An enzyme is very selective in the reaction it catalyzes and

has a shape that determines the enzymes

specificity.

The specific reactant that an enzyme acts on iscalled the enzymes substrate.

A substrate fits into a region of the enzyme called

the active site. Enzymes are specific because their active site fits

only specific substrate molecules.


A specific enzyme catalyzes each cellular reaction


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A specific enzyme catalyzes each cellular reaction

The following figure illustrates thecatalytic cycle of an enzyme.


Figure 5.14_s1

1 Enzyme available

with empty active


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Enzyme

(sucrase)

Active site

with empty active

site

Figure 5.14_s2

1 Enzyme available

with empty active


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2

Enzyme

(sucrase)

Active site

with empty active

site

Substrate

(sucrose)

Substrate binds

to enzyme with

induced fit

Figure 5.14_s3

1 Enzyme available

with empty active


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3

2

Enzyme

(sucrase)

Active site

with empty active

site

Substrate

(sucrose)

Substrate binds

to enzyme with

induced fit

Substrate is

converted to

products

H2O

Figure 5.14_s4

1 Enzyme available

with empty active


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4

3

2

Products are

released

Fructose

Glucose

Enzyme

(sucrase)

Active site

with empty active

site

Substrate

(sucrose)

Substrate binds

to enzyme with

induced fit

Substrate is

converted to

products

H2O



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reaction

For every enzyme, there are optimalconditions under which it is most effective.

Temperature affects molecular motion.

An enzymes optimal temperatureproduces the highest rate of contact

between the reactants and the enzymes

active site.

Most human enzymes work best at 35

40C.

The optimal pH for most enzymes is near 2012 Pearson Education, Inc.



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reaction

Many enzymes require nonprotein helperscalled cofactors, which

bind to the active site and

function in catalysis. Some cofactors are inorganic, such as zinc,

iron, or copper.

If a cofactor is an organic molecule, such asmost vitamins, it is called a coenzyme.


Enzyme inhibitors can regulate enzyme activity in acell


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cell

A chemical that interferes with anenzymes activity is called an inhibitor.

Competitive inhibitors

block substrates from entering theactive site and

reduce an enzymes productivity.




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cell

Noncompetitive inhibitors bind to the enzyme somewhere other

than the active site,

change the shape of the active site,and

prevent the substrate from binding.


Figure 5.15A


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Substrate

Enzyme

Allosteric site

Active site

Normal binding of substrate

Competitive

inhibitorNoncompetitive

inhibitor

Enzyme inhibition



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cell

Enzyme inhibitors are important inregulating cell metabolism.

In some reactions, the product may act

as an inhibitor of one of the enzymes inthe pathway that produced it. This is

called feedback inhibition.


Figure 5.15B


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Feedback inhibition

Starting

molecule

Product

Enzyme 1 Enzyme 2 Enzyme 3

Reaction 1 Reaction 2 Reaction 3A B C D

CONNECTION: Many drugs, pesticides, andpoisons are enzyme inhibitors


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poisons are enzyme inhibitors

Many beneficial drugs act as enzymeinhibitors, including

Ibuprofen, inhibiting the production ofprostaglandins,

some blood pressure medicines, some antidepressants,

many antibiotics, and

protease inhibitors used to fight HIV. Enzyme inhibitors have also been developed

as pesticides and deadly poisons for

chemical warfare 2012 Pearson Education, Inc. Figure 5.16


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MECHANISM ACTION:


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There are 2 main hypotheses explaining of

enzyme action.


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Each enzyme is specificfor one and ONLYone substrate (one lock - one key)

active site: part of the enzyme that fits with

the substrate Note that the active site has a specific fit for

this particular substrate and no other.

This theory has some weaknesses, but itexplains many basic things about enzyme

function.


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The induced-fit theory assumes that the substrateplays a role in determining the final shape of the

enzyme and that the enzyme is partially flexible.

This explains why certain compounds can bind tothe enzyme but do not react because the enzyme

has been distorted too much.

Other molecules may be too small to induce the

proper alignment and therefore cannot react. Only the proper substrate is capable of inducing the

proper alignment of the active site.


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http://en.wikipedia.org/wiki/Image:Induced_fit_diagram.svg


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In the graphic, the substrate is represented by themagenta molecule, the enzyme protein is

represented by the green and cyan colors.

The cyan colored protein is used to more sharply

define the active site. The protein chains are flexible and fit around the

substrate.


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The advantages of the induced fit mechanism arise dueto the stabilizing effect of strong enzyme binding


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to the stabilizing effect of strong enzyme binding.

There are two different mechanisms of substrate

binding;uniform binding which has strong substratebinding, and differential bindingwhich has strongtransition state binding.

The stabilizing effect of uniform binding increases bothsubstrate and transition state binding affinity and

differential binding increases only transition statebinding affinity.


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Both are used by enzymes and have been

evolutionarily chosen to minimize the G of thereaction.

Enzymes which are saturated, ie. have a high affinitysubstrate binding, require differential binding toreduce the G, whereas largely substrate unboundenzymes may use either differential or uniformbinding.

How do enzymes work?


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How do enzymes work?

substrate: molecules upon which an enzymeacts. The enzyme is shaped so that it can only

lock up with a specific substrate molecule.

enzyme

substrate -------------> product


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The diagram shows time on the horizontal axis and

the amount of energy in the chemicals involved in achemical reaction on the vertical axis.

The point if this diagram again is that without the

enzyme, much more activation energy is required to

get a chemical reaction to take place.


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Factors Influencing Enzyme Activity


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Factors Influencing Enzyme Activity

pH: the optimum (best) in most living things isclose to 7 (neutral).

High or low pH levels usually slow enzyme

activity


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Temperature: strongly influences enzyme

activity optimum (best) temperature for maximum

enzyme function is usually about 35-40 C.

Reactions proceed slowly below optimal

temperatures.

Above 45 C. most enzymes are denatured(change in their shape so the enzyme active site

no longer fits with the substrate and the enzyme

can't function)


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METABOLISM


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METABOLISM

Metabolism is the sum of all biochemicalreactions occurring in living cells.

These reactions can be divided into two main

groups:

1) ANABOLISM 2) CATABOLISM


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Involves the synthesis

of complex molecules

from simpler moleculeswhich requires energy

input.

Involves the

breakdownof complex

molecules into simpler

molecules involving

hydrolysis or oxidation

and the release of

energy.


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Energy releasing processes, ones that "generate"energy, are termed exergonic reactions.

Reactions that require energy to initiate thereaction are known as endergonic reactions.

All natural processes tend to proceed in such adirection that the disorder or randomness of theuniverse increases


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In an exergonic reaction the change is freeenergy is represented by a negative number (-

G), indicating free energy is released during

the reaction.


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This kind of reaction is not termed a

spontaneous reaction. In order to go from theinitial state to the final state a considerable

amount of energy must be imparted to the

system.

These kinds of reactions are associated with a

positive number (+G).


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The speed Vmeans the number of reactions per


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second that are catalyzed by an enzyme.

With increasing substrate concentration [S], theenzyme is asymptotically approaching its

maximum speed Vmax, but never actually

reaching it.

Because of that, no [S] for Vmax can be given. Instead, the characteristic value for the enzyme

is defined by the substrate concentration at its

half-maximum speed (Vmax/2).

This KM value is also called Michaelis-Menten

constant.


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Vo = Vmax

KM

Vo = Initial reaction velocity

Vmax= Maximum velocity

Km= Michaelis constant

[S] = Substrate concentration


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A non protein component of enzymes is called the

cofactor.

If the cofactor is organic, then it is called a

coenzyme.

Coenzymes are relatively small moleculescompared to the protein part of the enzyme.

Many of the coenzymes are derived from vitamins.

The coenzymes make up a part of the active site,since without the coenzyme, the enzyme will not

function.


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In the graphic on the left is the structure forthe coenzyme, NAD+, Nicotinamide

Adenine Dinucleotide.

Nicotinamide is from the niacin vitamin.

The NAD+ coenzyme is involved with

many types of oxidation reactions where

alcohols are converted to ketones or

aldehydes.


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Coenzyme Q10 is a fat-soluble nutrient alsoknown as CoQ10, vitamin Q10,ubidecarenone, or ubiquinone.

It is a natural product of the human body that

is primarily found in the mitochondria, whichare the cellular organelles that produceenergy.

It occurs in most tissues of the human body;

however, the highest concentrations arefound in the heart, liver, kidneys, andpancreas.

Ubiquinone takes its name from a

combination of the word ubiquitous meaning

Quinones are substances found in all


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Quinones are substances found in allplants and animals.

The variety found in humans has a 10-unitside chain in its molecular structure.

Apart from the important process that

provides energy, CoQ10 also stabilizes cellmembranes and acts as an antioxidant.

In this capacity, it destroys free radicals,which are unstable molecules that can

damage normal cells.


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Enzyme inhibitors are molecules thatinteract in some way with the enzyme to

prevent it from working in the normal

manner. There are a variety of types of inhibitors

including: nonspecific, irreversible,

reversible - competitive and noncompetitive. Poisons and drugs are examples of enzyme

inhibitors.


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A nonspecific inhibition effects all enzymes in thesame way.

Non-specific methods of inhibition include any

physical or chemical changes which ultimately

denaturesthe protein portion of the enzyme andare therefore irreversible.


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Temperature:Usually, the reaction rate increases with

temperature, but with enzyme reactions, a point is

reached when the reaction rate decreases with

increasing temperature.

At high temperatures the protein part of the enzyme

begins to denature, thus inhibiting the reaction.


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A competitive inhibitor is any compound whichclosely resembles the chemical structure andmolecular geometry of the substrate.

The inhibitor competes for the same active site asthe substrate molecule.

The inhibitor may interact with the enzyme at theactive site, but no reaction takes place.


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The inhibitor is "stuck" on the enzyme andprevents any substrate molecules fromreacting with the enzyme.

However, a competitive inhibition is usuallyreversible if sufficient substrate molecules areavailable to ultimately displace the inhibitor.

Therefore, the amount of enzyme inhibitiondepends upon the inhibitor concentration,

substrate concentration, and the relativeaffinities of the inhibitor and substrate for theactive site.


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A noncompetitive inhibitor is a substance thatforms strong covalent bonds with an enzymeand consequently may not be displaced bythe addition of excess substrate.

Therefore, noncompetitive inhibition isirreversible.

A noncompetitive inhibitor may be bonded at,near, or remote from the active site. In anycase, the basic structure of the enzyme ismodified to the degree that it ceases to work.


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If the inhibition is at a place remote from the activesite, this is called allosteric inhibition.

Allosteric means "other site" or "other structure".

The interaction of an inhibitor at an allosteric site

changes the structure of the enzyme so that the activesite is also changed.


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There are approximately 3000 enzymes whichhave been characterised.

These are grouped into six main classesaccording to the type of reaction catalysed.

At present, only a limited number are used inenzyme electrodes or for other analyticalpurposes.

1.Oxidoreductases


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These enzymes catalyse oxidation andreduction reactions involving the transfer

of hydrogen atoms or electrons.

The following are of particularimportance in the design of enzyme

electrodes.

This group can be further divided into 4

main classes.

oxidases


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catalyse hydrogen transfer from the

substrate to molecular oxygen producing

hydrogen peroxide as a by-product. An

example of this is FAD dependent

glucose oxidase which catalyses the

following reaction:

b-D-glucose + O2 = gluconolactone +H2O2

dehydrogenases


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y g

catalyse hydrogen transfer fromthe substrate to a nicotinamide

adenine dinucleotide cofactor

(NAD+). An example of this islactate dehydrogenase which

catalyses the following reaction:

Lactate + NAD+ = Pyruvate +NADH + H+

peroxidases

catalyse oxidation of a substrate by hydrogen


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catalyse oxidation of a substrate by hydrogen

peroxide.An example of this type of enzyme is horseradish

peroxidase which catalyses the oxidation of a

number of different reducing substances (dyes,

amines, hydroquinones etc.) and the concomitantreduction of hydrogen peroxide.

The reaction below illustrates the oxidation of

neutral ferrocene to ferricinium in the presence of

hydrogen peroxide:

2[Fe(Cp)2] + H2O2 + 2H+= 2[Fe(Cp)2]+ + 2

H2O

oxygenases


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catalyse substrate oxidation by

molecular oxygen.

The reduced product of the reactionin this case is water and not

hydrogen peroxide.

An example of this is the oxidation oflactate to acetate catalysed by

lactate-2-monooxygenase.

=

yg

2.Transferases


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These enzymes transfer C, N, P orS containing groups (alkyl, acyl,

aldehyde, amino, phosphate or

glucosyl) from one substrate toanother.

Transaminases, transketolases,

transaldolases and transmethylasesbelong to this group.

3.Hydrolases


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y

These enzymes catalyse cleavagereactions or the reverse fragmentcondensations.

According to the type of bond cleaved,a distinction is made betweenpeptidases, esterases, lipases,

glycosidases, phosphatases and soon.

Examples of this class of enzyme

include; cholesterol esterase alkaline

4.Lyases


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y

These enzymes non-hydrolyticallyremove groups from their

substrates with the concomitant

formation of double bonds oralternatively add new groups across

double bonds.

5.Isomerases


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These enzymes catalyse intramolecularrearrangements and are subdivided into;

oracemases

oepimerases

omutases

oc is-t rans-isomerases

An example of this class of enzyme is

glucose isomerase which catalyses theisomerisation of glucose to fructose.

6.Ligases


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Ligases split C-C, C-O, C-N, C-S and C-halogen bonds without hydrolysis or

oxidation.

The reaction is usually accompanied by

the consumption of a high energy

compound such as ATP and other

nucleoside triphosphates.

An example of this type of enzyme is

pyruvate carboxylase which catalyses

the following reaction:

IEC Classification of Enzymes

Group Name Type of Reaction Catalyzed


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Oxidases or

Dehydrogenases

Oxidation-reduction

reactions

TransferasesTransfer of functional

groups

Hydrolases Hydrolysis reactions

LyasesAddition to double bonds or

its reverse

Isomerases Isomerization reactions

Ligases or SynthetasesFormation of bonds with

ATP cleavage


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Enzymes do NOT change the equilibrium position of thereaction, just the speed at which equilibrium is attained.

Most are globular or soluble.

Stereospecific (can recognize certain isomers only) due tothe fact that amino acids of the active site are chiral

themselves. Substrate/s bind in hydrophobic cleft (active site) between

several domains where catalysis occurs: Van der Waals forces

Hydrophobic interactions

Electrostatic interactions

Active site has structure that is complimentary in structure tothe structure of its substrate.

Most are proteins, some are RNA.


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p ,

Biological catalysts.

E + S ES EP E + P Not changed by the reaction overall Much higher reaction rates than uncatalyzed reactions.Allow for biochemical reactions to occur under very mild

conditions (temperature, near-neutral pH, 1 atm pressure)

High yield of products (few side reactions or by-products)

Very specific reactions (specific for its substrate or a family ofrelated substrates)

Often a regulated functions:

allosteric activation or inhibition covalent modification (phosphorylation changes) enzyme expression controlled or cleavage of proenzyme

controlled.


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Preparatory Reaction


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Documents

Chapter 3 and 4 Nutrition, Culture and Enzymes