Transcript
Page 1: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

•Energy – the ability to do work or bring about a change•Cells need energy to maintain their organization•Cells need energy to carry out reactions used to grow, develop, and reproduce

Page 2: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Forms of energy:•Kinetic energy – energy of motion•Ex: you raise your arm

•Potential energy – stored energy; capable of producing energy, but not being used yet•Ex: food we eat has potential energy

•Chemical energy – composed or organic molecules such as carbohydrates•Ex: food we eat, ATP

Page 3: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

•First law of thermodynamics (the law of conservation of energy) – energy cannot be created or destroyed, but it can be changed from one form to another•Energy flows; it does not cycle•As materials change from one form of energy to another, some energy is given off as heat (a form of energy)

Page 4: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

•Second law of thermodynamics – energy cannot be changed from one form to another without a loss of usable energy•Heat given off through the conversion of chemical energy to kinetic energy is not a usable form of energy•For this reason, living things are dependent upon an outside source of energy – the sun

Page 5: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Metabolic Pathways and Enzymes• Cellular reactions are usually part of a

metabolic pathway, a series of linked reactions• Many reactions have molecules in common• Energy can be released in small amounts

rather than all at once• Illustrated as follows:

E1 E2 E3 E4 E5 E6

A → B → C → D → E → F → G• Letters A-F are reactants or substrates, B-G are

the products in the various reactions, and E1-E6 are enzymes.

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter8/animations.html

Page 6: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• Enzyme - a protein molecule that functions as an organic catalyst to speed a chemical reaction.

• An enzyme brings together particular molecules and causes them to react.

• The reactants in an enzymatic reaction are called the substrates for that enzyme.

• For series of reactions below, A is substrate for E1 and B is product. B then becomes substrate for E2 and C is product. Continues to end of pathway.

E1 E2 E3 E4 E5 E6

A → B → C → D → E → F → G

Page 7: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• Energy of activation (Ea) - the energy that must be added to cause molecules to react with one another

• Enzyme lowers the amount of energy required for reaction to occur

• Enzymes allow reactions to take place at lower temperatures – otherwise, reactions would not be able to occur at normal body temperatures

Page 8: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Energy of activation (Ea)

When no enzyme is present – more energy required

When an enzyme is added – less energy required

Page 9: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Enzyme-Substrate Complexes• Every reaction in a cell requires a specific

enzyme.• Enzymes are named for their substrates:

Substrate Enzyme

Lipid Lipase

Ureas Urease

Maltose Maltase

Ribonucleic acid Ribonuclease

Page 10: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• Active site – part of enzyme that attaches to substrate• Active site may undergo a slight change in

shape in order to accommodate the substrate(s)

• The enzyme and substrate form an enzyme-substrate complex during the reaction.

• The enzyme is not changed by the reaction (active site returns to its original state), and it is free to act again.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

Page 11: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Enzymatic reaction

Substrate is broken down into smaller products

Substrates are combined into a larger product

Page 12: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Induced fit model

•Because the enzyme must undergo a slight change in shape to fit with the substrate, this is known as the induced fit model.

Page 13: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Factors Affecting Enzymatic Speed

• Substrate concentration

• Temperature and pH

• Enzyme concentration

• Enzyme inhibition

• Competitive inhibitors

• Non-competitive inhibitors

• Enzyme co-factors

Page 14: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

•Substrate concentration:

•Enzyme activity increases as substrate concentration increases because there are more collisions between substrate molecules and the enzyme.

•When active sites on enzymes are filled almost continuously with substrate, rate of activity cannot increase further.

Page 15: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• Temperature and pH:• As the temperature rises, enzyme activity

increases because more collisions occur between enzyme and substrate.

• If the temperature is too high, enzyme activity levels out and then declines rapidly because the enzyme is denatured.

• When enzyme is denatured, its shape changes and it can no longer bind to substrate.

• Each enzyme has an optimal pH and temperature at which the rate of reaction is highest.

Page 16: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Rate of an enzymatic reaction as a function of temperature and pH

Page 17: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• Enzyme Concentration:

• A cell regulates which enzymes are present or active at any one time and the quantity of enzyme present by turning on of off genes

• Another way to control enzyme activity is to activate or deactivate the enzyme, such as through phosphorylation (removal of phosphate group).

Page 18: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• Enzyme Inhibition:• Occurs when an active enzyme is prevented

from combining with its substrate.• When the product of a metabolic pathway is

in abundance, it binds competitively with the enzyme’s active site, a simple form of feedback inhibition.

• Other metabolic pathways are regulated by the end product binding to an allosteric site (another area of enzyme).

• Poisons such as cyanide are often enzyme inhibitors; penicillin is an enzyme inhibitor for bacteria.

Page 19: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Feedback inhibition

Page 20: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

When there is a sufficient amount of the end product, some of the product binds to the allosteric site on the enzyme, the active site changes shape, the reactant cannot bind, and the end product is no longer produced. http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter8/animations.html

Page 21: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Competitive inhibitors:•Have a similar shape to the substrate & fit into the active site of the enzyme•Don’t take part in the reaction•Block active site so substrate can’t enter

Non-competitive inhibitors:•Do not have the same shape as the substrate & do not compete for the active site•Bind at some other point on the enzyme molecule, which still changes the shape of the active site so enzyme-substrate complex cannot be formed.

http://www.stolaf.edu/people/giannini/flashanimat/enzymes/allosteric.swf

Animation

Page 22: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• Enzyme Cofactors• Presence of enzyme cofactors may be

necessary for some enzymes to carry out their functions.

• Inorganic metal ions, such as copper, zinc, or iron function as cofactors for certain enzymes.

• Organic molecules, termed coenzymes, must be present for other enzymes to function.

• Some coenzymes are vitamins; certain vitamin deficiencies result in a lack of certain enzymatic reactions.

Page 23: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

The ATP cycle

Page 24: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

ATP (adenosine triphosphate)• The energy currency of cells. • A nucleotide made of the following:

• Adenine• Ribose (a sugar)• Three phosphate groups

• Constantly regenerated from ADP (adenosine diphosphate) after energy is expended by the cell.

• Pneumonic devices – ATP – a triple phosphate

- ADP – a double phosphatehttp://www.stolaf.edu/people/giannini/flashanimat/metabolism/

atpsyn2.swf

Page 25: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Advantages of ATP:1) It can be used in many types of

reactions.2) When ATP → ADP + P, energy released

is sufficient for cellular needs and little energy is wasted.

3) ATP is coupled to endergonic reactions (requires an input of energy) in such a way that it minimizes energy loss.

Page 26: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Overview of Cellular Respiration• Makes ATP molecules• Releases energy in several reactions

• Glycolysis • Transition reaction• Citric acid cycle (Kreb’s cycle)• Electron transport system

• An aerobic process that requires O2

Page 27: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

•Cellular respiration takes the potential chemical energy in the bonds of glucose and transforms it into the potential chemical energy in the bonds of ATP.•ATP molecules store usable chemical energy to drive life processes through coupled reactions.

Page 28: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

•It is an oxidation-reduction reaction, or redox reaction for short.•Oxidation is the loss of electrons; hydrogen atoms are removed from glucose.•Reduction is the gain of electrons; oxygen atoms gain electrons.•Remember OIL RIG (oxidation is loss, reduction is gain)

Page 29: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Enzymes involved:

• NAD+

• Nicotinamide adenine dinucleotide

• Accepts 2 electrons & 1 H+ to become NADH

• FAD

• Flavin adenine dinucleotide (sometimes used instead of NAD+)

• Accepts 2 electrons & 2 H+ to become FADH2

Page 30: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

The NAD+ cycle

Page 31: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Phases of Cellular Respiration

• Four phases:• Glycolysis • Transition reaction• Citric acid cycle (Kreb’s cycle)• Electron transport system

(If oxygen is not available, fermentation occurs in the cytoplasm instead of proceeding to cellular respiration.)

Page 32: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

The four phases of complete glucose breakdown

Page 33: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Glycolysis

• Occurs in the cytoplasm (outside the mitochondria)

• Glucose 2 pyruvate molecules.

• Universally found in all organisms

• Does not require oxygen.

http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html

Page 34: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used
Page 35: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used
Page 36: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used
Page 37: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Energy-Investment Steps• Requires 2 ATP to start process and activate

glucose• Glucose splits into two C3 molecules (PGAL)• Each C3 molecule undergoes the same series of

reactions.

Page 38: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Energy-Harvesting Steps• PGAL is oxidized by the removal of electrons

by NAD+; phosphate group is attached to each PGAL as well (phosphorylation)

• Removal of phosphate from 2 PGAP by 2 ADP produces 2 ATP, and 2 PGA molecules

Page 39: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

•Removal of water results in 2 PEP molecules•Removal of phosphate from 2 PEP by 2 ADP produces 2 ATP molecules and 2 pyruvate molecules

Page 40: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Glycolysis summary

• Inputs:• Glucose

• 2 NAD+

• 2 ATP

• 4 ADP + 2 P

• Outputs:• 2 pyruvate

• 2 NADH

• 2 ADP

• 2 ATP (net gain)

•When oxygen is available, pyruvate enters the mitochondria, where it is further broken down•If oxygen is not available, fermentation occurs

Page 41: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Inside the Mitochondria• Structure of mitochondia:

• Has a double membrane, with an intermembrane space between the two layers.

• Cristae are folds of inner membrane

• The matrix, the innermost compartment, which is filled with a gel-like fluid.

• The transition reaction and citric acid cycle occur in the matrix; the electron transport system is located in the cristae.

Page 42: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Mitochondrion structure and function

Page 43: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Transition Reaction• Is the transition between glycolysis and the citric

acid cycle.• Pyruvate (made during glycolysis) is converted to

acetyl CoA, and CO2 is released• NAD+ is converted to NADH + H+

• The transition reaction occurs twice per glucose molecule.

Page 44: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Transition reaction inputs and outputs per glucose molecule

• Inputs:

• 2 pyruvate

• 2 NAD+

• Outputs:

• 2 acetyl groups

• 2 CO2

• 2 NADH

http://www.science.smith.edu/departments/Biology/Bio231/krebs.html

Page 45: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Citric Acid Cycle (aka Kreb’s Cycle)• Occurs in the matrix of the mitochondria.

• C2 acetyl group (produced during transition reaction) joins a C4 molecule, and C6 citrate results.

• Each acetyl group gives off 2 CO2 molecules.

• NAD+ accepts electrons in three sites and FAD accepts electrons once.

• Substrate-level phosphorylation results in a gain of one ATP per every turn of the cycle; it turns twice per glucose, so a net of 2 ATP are produced.

• The citric acid cycle produces four CO2 per molecule of glucose.

Page 46: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used
Page 47: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Citric acid cycle

Page 48: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Citric acid cycle inputs and outputs per glucose molecule

• Inputs:

• 2 acetyl groups

• 6 NAD+

• 2 FAD

• 2 ADP + 2 P

• Outputs:

• 4 CO2

• 6 NADH

• 2 FADH2

• 2 ATP

Page 49: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Electron Transport System (ETS)

• Located in the cristae of mitochondria

• Series of protein carriers pass electrons from one to the other.

• NADH and FADH2 carry electrons picked up during glycolysis, transition reaction, & citric acid cycle

• NADH and FADH2 enter the ETS.

Page 50: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• As a pair of electrons is passed from carrier to carrier, energy is released and is used to form ATP molecules by oxidative phosphorylation (term used to describe production of ATP as a result of energy released by ETS).

• Oxygen receives electrons at the end of the ETS, which combines with hydrogen to form water:

½ O2 + 2 e- + 2 H+ → H2O

Page 51: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Overview of the electron transport system

Page 52: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Organization of Cristae• The ETS consists of 3 protein complexes and 2

mobile carriers.

– Mobile carriers transport electrons between the complexes.

– Energy is released by electrons as they move down carriers

– H+ are pumped from the matrix into the intermembrane space of the mitochondrion.

• Produces a very strong electrochemical gradient - few H+ in the matrix and many H+ in the intermembrane space.

Page 53: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

• The cristae also contain an ATP synthase complex – Hydrogen ions flow through ATP synthase

complex down their gradient from the intermembrane space into the matrix.

– Flow of 3 H+ through ATP synthase complex causes the ATP synthase to synthesize ATP from ADP + P.

– This process of making ATP is called chemiosmosis, because ATP production is tied to an electrochemical gradient (H+ gradient)

– Once formed, ATP molecules are transported out of the mitochondrial matrix.

Page 54: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used
Page 55: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

http://www.science.smith.edu/departments/Biology/Bio231/etc.html

http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter9/animations.html

Cellular respiration song

Page 56: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used
Page 57: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Energy Yield from Glucose Metabolism• Per glucose molecule:

– 10 NADH take electrons to the ETS 3 ATP from each

– 2 FADH2 take electrons to the ETS 2 ATP from each

• Electrons carried by NADH produced during glycolysis are shuttled to the electron transport chain by an organic molecule (mechanism of delivery may vary # of ATP produced by ETS).

Page 58: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Accounting of energy yield per glucose molecule breakdown

Page 59: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used
Page 60: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Fermentation• Occurs when oxygen is not available.

• During fermentation, the pyruvate formed by glycolysis is reduced to alcohol and CO2, or one of several organic acids, such as lactate.

• Fermentation uses NADH and regenerates NAD+, which are free to pick up more electrons during early steps of glycolysis; this keeps glycolysis going.

• Occurs in anaerobic bacteria, fungus, & human muscle cells.

http://instruct1.cit.cornell.edu/Courses/biomi290/MOVIES/GLYCOLYSIS.HTML

Page 61: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used
Page 62: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Fermentation

•Before fermentation, glycolysis produces 2 pyruvate molecules.•Then pyruvate is reduced by NADH into lactate or alcohol & CO2.

Page 63: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Advantages and Disadvantages of Fermentation

• Fermentation can provide a rapid burst of ATP in muscle cells, even when oxygen is in limited supply.• For bacteria, glycolysis and fermentation is

the main energy source• Lactate, however, is toxic to cells.• Initially, blood carries away lactate as it forms;

eventually lactate builds up, lowering cell pH, and causing muscles to fatigue.

• Oxygen debt occurs, and the liver must reconvert lactate to pyruvate.

Page 64: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Efficiency of Fermentation

• Two ATP produced during fermentation are equivalent to 14.6 kcal; complete oxidation of glucose to CO2 and H2O represents a yield of 686 kcal per molecule of glucose.

• Thus, fermentation is only 2.1% efficient compared to cellular respiration (which is 39% efficient).

• (14.6/686) x 100 = 2.1%

Page 65: Energy – the ability to do work or bring about a change Cells need energy to maintain their organization Cells need energy to carry out reactions used

Glycolysis and Fermentation inputs and outputs per glucose molecule

• Inputs (into glycolysis):

• Glucose

• 2 ATP

• 4 ADP + 2 P

• Outputs:

• 2 lactate (fermentation) or

• 2 alcohol & 2 CO2

(fermentation)

• 2 ADP (glycolysis)

• 2 ATP (net gain) (glycolysis)


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