Bioenergetics

Sengupta 1

Bioenergetics

1.Compare the difference between potential and kinetic energy.

2.Define the two laws of thermodynamics and explain how they relate to biological systems.

3.Explain how ATP functions as an energy shuttle. 4.Describe how enzymes speed up chemical reactions. 5.Describe how cellular respiration produces energy that can be stored in ATP.

6.Describe the three main stages of cellular respiration. 7.Discuss the importance of oxidative phosphorylation in producing ATP.

8.Compare ATP generation from substrate level phosphorylation and oxidative phosphorylation.

9.Compare cellular respiration and fermentation.

Learning Objectives

Energy Transformation in cells

•  Cells are small units, a chemical factory, housing thousands of chemical reactions.

•  Cells use these chemical reactions for –  cell maintenance, –  manufacture of cellular parts, and –  cell replication.

Energy

Energy is the capacity to cause change or to perform work. There are two kinds of energy:

• Kinetic energy is the energy of motion. • Potential energy is energy that matter

possesses as a result of its location or structure.

Fuel Energy conversion Waste products

Gasoline

Oxygen

Oxygen

Glucose

+

+

+

+

Heat energy

Combustion Kinetic energy of movement

Energy conversion in a car

Energy conversion in a cell

Energy for cellular work

Cellular respiration

ATP ATP

Heat energy

Carbon dioxide

Carbon dioxide

Water

Water

•  Heat or thermal energy, is a type of kinetic energy associated with the random movement of atoms or molecules.

•  Light is kinetic energy, and can be harnessed to power photosynthesis.

•  Electrical energy used in the nervous system. •  Chemical energy is responsible for all the

biochemical reactions in the cell like ATP

Types of Energy used by Cells

Bioenergetics

Sengupta 2

Thermodynamics

•  “Thermodynamics, science of the relationship between heat, work, temperature, and energy. In broad terms, thermodynamics deals with the transfer of energy from one place to another and from one form to another. The key concept is that heat is a form of energy corresponding to a definite amount of mechanical work”.

Encyclopedia Britannica

•  Scientists use the word –  system for the matter under study and –  surroundings for the rest of the universe.

9

Biological Thermodynamics

• Quantitative study of the energy transductions that occur in and between living organisms, structures, and cells and of the nature and function of the chemical processes underlying these transductions.

• Biological thermodynamics may address the

question of whether the benefit associated with any particular phenotypic trait is worth the energy investment it requires.

Energy Transformations

Two laws govern energy transformations in living organisms.

–  The first law of thermodynamics, energy in the universe is constant, (statement of the conservation of energy)and

–  The second law of thermodynamics, energy conversions increase the disorder of the universe.

• Entropy is the measure of disorder, or randomness.

Energy  Transforma.on   Energy Transformations in Cells

•  Cells use oxygen in reactions that release energy from fuel molecules.

•  In cellular respiration, the chemical energy stored in organic molecules is converted to a form that the cell can use to perform work.

Bioenergetics

Sengupta 3

Energy and Chemical reactions

•  Chemical reactions either –  release energy (exergonic reactions)

or –  require an input of energy and store

energy (endergonic reactions).

Exergonic reactions

Exergonic reactions release energy. –  These reactions release the energy in covalent

bonds of the reactants –  Burning wood releases the energy in glucose as

heat and light –  Cellular respiration

•  involves many steps, •  releases energy slowly, and •  uses some of the released energy to produce ATP.

Exergonic Reaction

Reactants

Energy Products

Amount of energy

released

Pot

entia

l ene

rgy

of m

olec

ules

Endergonic Reactions

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 chemical

energy.

Endergonic Reaction

Reactants

Energy

Products

Amount of energy

required

Pot

entia

l ene

rgy

of m

olec

ules

Photosynthesis : endergonic reaction

Photosynthesis is a type of endergonic process.

–  Energy-poor reactants, carbon dioxide, and water are used.

–  Energy is absorbed from sunlight. –  Energy-rich sugar molecules are produced.

Bioenergetics

Sengupta 4

Metabolism

•  A living organism carries out thousands of endergonic and exergonic chemical reactions.

•  Metabolism :The total of an organism’s chemical reactions.

•  Metabolism = Anabolism + Catabolism •  A metabolic pathway is a series of chemical

reactions that either –  builds a complex molecule or –  breaks down a complex molecule into simpler

compounds.

The  Energy  Cycle  

Metabolic  pathways  

Breakdown Proteins to Amino Acids, Starch to Glucose

Synthesis Amino Acids to Proteins, Glucose to Starch

Energy Coupling

•  Energy coupling uses the –  energy released from exergonic reactions

to drive –  essential endergonic reactions, –  usually using the energy stored in ATP

molecules.

•  ATP, adenosine triphosphate, powers

nearly all forms of cellular work.

•  ATP consists of

–  the nitrogenous base adenine,

–  the five-carbon sugar ribose, and

–  three phosphate groups.

The Energy Currency of the Cell Renewable cellular energy: ATP

•  ATP is a renewable source of energy for the cell

•  In the ATP cycle, energy released in an exergonic reaction, such as the breakdown of glucose,is used in an endergonic reaction to generate ATP

Bioenergetics

Sengupta 5

ATP drives cellular work

•  Hydrolysis of ATP releases energy by transferring 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

Adenine P P P

Phosphate group

ATP: Adenosine Triphosphate

Ribose

ADP: Adenosine Diphosphate

P P P Energy

H2O Hydrolysis

Ribose

Adenine P P P

Phosphate group

ATP: Adenosine Triphosphate ATP drives cellular work

•  There are three main types of cellular work: 1.  chemical, 2.  mechanical, and 3.  transport

•  ATP drives all three of these types of work

ATP ATP ATP

ADP ADP ADP P P P

P

P

P

P P P

Chemical work Mechanical work Transport work

Reactants

Motor protein

Solute

Membrane protein

Product

Molecule formed Protein filament moved Solute transported

HOW ENZYMES FUNCTION

Bioenergetics

Sengupta 6

Biological Catalysts

•  Although biological molecules possess much potential 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).

The Energy of Activation

•  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 –  but could also kill a cell.

Enzymes lower energy of activation

Enzymes • are usually proteins, although some RNA

molecules can function as enzymes. • function as biological catalysts by lowering the

EA needed for a reaction to begin, • increase the speed of a reaction without being

consumed by the reaction

Activation energy barrier

Reactant

Products

Reaction without enzyme

Ene

rgy

Activation energy barrier reduced by enzyme

Reactant

Products

Reaction with enzyme

Ene

rgy

Enzyme

Metabolic reaction in a cell with and without enzyme

Reactants

Products

Ene

rgy

Progress of the reaction

a

b

c

Bioenergetics

Sengupta 7

Enzymes have a specific shape

•  An enzyme –  is very selective in the reaction it

catalyzes and –  has a shape that determines the

enzyme’s specificity. •  The specific reactant that an enzyme acts

on is called the enzyme’s 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.

Figure 5.14_s2

2

1

Enzyme (sucrase)

Active site

Enzyme available with empty active site

Substrate (sucrose)

Substrate binds to enzyme with induced fit

Figure 5.14_s3

3

2

1

Enzyme (sucrase)

Active site

Enzyme available with empty active site

Substrate (sucrose)

Substrate binds to enzyme with induced fit

Substrate is converted to products

H2O

4

3

2

1

Products are released

Fructose

Glucose Enzyme (sucrase)

Active site

Enzyme available with empty active site

Substrate (sucrose)

Substrate binds to enzyme with induced fit

Substrate is converted to products

H2O

A �my�l�a�s �e

catalase lactase

Some common enzymes

http://mm.rcsb.org

Conditions for optimum enzyme activity

Every enzyme has optimal conditions under which it is most effective.

•  Temperature affects molecular motion. –  An enzyme’s optimal temperature produces the

highest rate of contact between the reactants and the enzyme’s active site.

–  Most human enzymes work best at 35–40ºC. –  But high temperature disrupts the structure

•  The optimal pH for most enzymes is near neutrality.

Bioenergetics

Sengupta 8

Enzyme activity

Four  Variables  

Temperature

pH

Enzyme Concentration

Substrate Concentration

Effect of heat on enzyme activity

Denaturing protein

IF ACTIVE SITE CHANGES SHAPE: SUBSTRATE NO LONGER FITS

Even if temperature lowered – enzyme cannot regain its correct shape

Rat

e of

Rea

ctio

n

Temperature  

0 20 30 50 10 40 60

40oC -denatures 5- 35oC Increase in Activity

<5oC - inactive

Environmental Conditions can Cause Changes in Shape (Denaturing)

Rat

e of

Rea

ctio

n

pH

1 3 4 2 5 6 7 8 9

Narrow pH optima

Disrupt Ionic bonds - Structure

Effect charged residues at active site

Cofactors and coenzymes

•  Many enzymes require nonprotein helpers called 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 as most vitamins, it is called a coenzyme.

Bioenergetics

Sengupta 9

Enzyme inhibitors

•  A chemical that interferes with an

enzyme’s activity is called an inhibitor.

•  Competitive inhibitors

–  block substrates from entering the active

site and

–  reduce an enzyme’s productivity.

Enzyme inhibitors

•  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.

Substrate

Enzyme

Allosteric site

Active site

Normal binding of substrate

Competitive inhibitor

Noncompetitive inhibitor

Enzyme  inhibi.on  Enzyme inhibitors regulate cell metabolism

•  Enzyme inhibitors are important in regulating cell metabolism.

•  In some reactions, the product may act as an inhibitor of one of the enzymes in the pathway that produced it. This is called feedback inhibition.

Feedback Inhibition

Feedback inhibition

Starting molecule

Product

Enzyme 1 Enzyme 2 Enzyme 3

Reaction 1 Reaction 2 Reaction 3 A B C D

Some  drugs,  pes.cides  and  poisons  are  enzyme  inhibitors

•  Many beneficial drugs act as enzyme inhibitors, including –  Ibuprofen, inhibiting the production of

prostaglandins, –  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.

Bioenergetics

Sengupta 10

The Marathoner and the Sprinter

The Marathoners and the Sprinters

Cellular respiration is the process by which cells produce energy aerobically

The different types of muscle fibers use different processes for making ATP

•  Slow-twitch fibers undergo aerobic respiration (in the presence of O2) respiration are reddish in color as it contains

myoglobin

•  Fast-twitch fibers undergo anaerobic respiration (in the absence of O2) respiration

Breathing and Cellular Respiration

Breathing

Lungs

Muscle cells carrying out Cellular Respiration

Bloodstream

Glucose + O2

CO2 + H2O + ATP

O2 CO2

CO2 O2

Connecting breathing and cellular respiration

Breathing and cellular respiration are closely related •  Breathing brings O2 into the body from the

environment •  O2 is distributed to cells in the bloodstream •  In cellular respiration, mitochondria use O2 to

harvest energy and generate ATP •  Breathing disposes of the CO2 produced as a

waste product of cellular respiration.

The human energy requirement

The human body uses energy from ATP for all its activities

–  The body needs a continual supply of energy to maintain basic functioning: to breathe, to keep heart pumping and maintain body temperature.

–  The brain requires 120 gm of glucose/day! –  ATP supplies energy (kilocalories) for voluntary

activities

–  An average adult human needs about 2,000 kcal of energy each day.

Cellular respiration and ATP molecules

• Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to form ATP. ▪ Cellular respiration

–  Can produce up to 32-34 ATP molecules from each glucose molecule and

–  captures only about 34% of the energy originally stored in glucose.

▪ Other foods (organic molecules) can also be used as a source of energy.

Bioenergetics

Sengupta 11

Breaking down Glucose

Glucose Oxygen Water Carbon dioxide

C6H12O6 O2 H2O ATP 6 6 6

+ Heat

CO2

What is kcal?

• A kilocalorie (kcal) is –  the quantity of heat required to raise the

temperature of 1 kilogram (kg) of water by 1oC,

–  the same as a food Calorie, and –  used to measure the nutritional values

indicated on food labels.

Activity kcal consumed per hour by a 67.5-kg (150-lb) person*

Running (8–9 mph)

Dancing (fast)

Bicycling (10 mph)

Swimming (2 mph)

Walking (4 mph)

Walking (3 mph)

Dancing (slow)

Driving a car

Sitting (writing)

*Not including kcal needed for body maintenance

979

510

490

408

341

245

204

61

28

How can energy be released from glucose?

• Energy can be released from glucose by simply burning it.

• The energy is dissipated as heat and light and is not available to living organisms.

How do cells tap energy from glucose?

• On the other hand, cellular respiration is the controlled breakdown of organic molecules.

• Energy is –  gradually released in small amounts, –  captured by a biological system, and –  stored in ATP.

The redox reaction in cells

• Movement of electrons from one molecule to another is an oxidation-reduction reaction, or redox reaction. In a redox reaction, –  the loss of electrons from one substance is

called oxidation, –  the addition of electrons to another substance

is called reduction, –  a molecule is oxidized when it loses one or

more electrons, and –  reduced when it gains one or more electrons.

Bioenergetics

Sengupta 12

The Process

• A cellular respiration equation is helpful to show the changes in hydrogen atom distribution.

• Glucose –  loses its hydrogen atoms and –  becomes oxidized to CO2.

• Oxygen –  gains hydrogen atoms and –  becomes reduced to H2O.

The Redox Reaction in Cells

Glucose + Heat

C6H12O6 O2 CO2 H2O ATP 6 6 6

Loss of hydrogen atoms (becomes oxidized)

Gain of hydrogen atoms (becomes reduced)

Mitochondria in Action

Occurs in Cytoplasm

Occurs in Matrix

Occurs across Cristae

Where does Cellular Respiration Occur?

What are the three phases of Cellular Respiration ?

•  Glycolysis •  Citric Acid Cycle •  Oxidative Phosphorylation

C6H12O6 CO2 O2 H2O

Glucose Oxygen Carbon dioxide

Water

+ 6 + 6 6

Reduction

Oxidation

Oxygen gains electrons (and hydrogens)

Glucose loses electrons (and hydrogens)

Bioenergetics

Sengupta 13

The role of Oxygen in Cellular Respiration

•  Cellular respiration can produce up to 38 ATP molecules for each glucose molecule consumed.

•  During cellular respiration, hydrogen and its bonding electrons change partners.

–  Hydrogen and its electrons go from glucose to oxygen, forming water.

–  This hydrogen transfer is why oxygen is so vital to cellular respiration.

Release of heat energy

1 2 H2 O2

H2O

Glucose and Oxygen

• Glucose

–  loses its hydrogen atoms and –  becomes oxidized to CO2.

• Oxygen –  gains hydrogen atoms and –  becomes reduced to H2O.

Controlled breaking of the glucose molecule to release energy

Glucose + Heat

C6H12O6 O2 CO2 H2O ATP 6 6 6

Loss of hydrogen atoms (becomes oxidized)

Gain of hydrogen atoms (becomes reduced)

The controlled breakdown of glucose

• There are other electron “carrier” molecules that function like NAD+. –  They form an energy ‘staircase’ where the

electrons pass from one to the next down the next level.

–  These electron carriers collectively are called the electron transport chain.

–  As electrons are transported down the chain, ATP is generated.

The molecules in the process

I. Enzymes are necessary to oxidize glucose and other foods. II.NAD+

–  is an important enzyme in oxidizing glucose,

–  accepts electrons, and –  becomes reduced to NADH.

Bioenergetics

Sengupta 14

•  NAD+ picks up one hydrogen atom and another single electron from carbohydrate, becoming NADH.

•  It will retain this form until it drops off its energetic electrons (and a proton) in a later stage of the energy-harvesting process.

NAD+ ATP and oxidative phosphorylation

NADH passes electrons to the electron transport chain.

–  As electrons “move” from carrier to carrier and finally to O2, energy is released in small quantities.

–  The energy released is used by the cell to make ATP.

The Electron Carrier NAD+

empty empty loaded

proton (oxidized)

used in later stage of respiration

used in later stage of respiration

goes to pick up more electrons

(reduced)

1. 2. NAD+ within a cell, along with two hydrogen atoms that are part of the food that is supplying energy for the body.

NAD+ is reduced to NAD by accepting an electron from a hydrogen atom. It also picks up another hydrogen atom to become NADH.

NADH carries the electrons to a later stage of respiration then drops them off, becoming oxidized to its original form, NAD+.

The energy gradient NADH

NAD+

Electron transport

chain

2e− Controlled release of energy for synthesis

of ATP

ATP

H+

2 H+ 2e−

H2O

O2 1/2

•  Uses two ATP molecules per glucose to split the six-carbon glucose.

•  Makes four additional ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP. Glycolysis produces a net of two

molecules of ATP per glucose molecule.

Glycolysis: substrate level phosphorylation

Figure 6.7A

Glucose

2 Pyruvate

2 ADP

2 P 2 NAD+

2 NADH

2 H+ ATP 2

Bioenergetics

Sengupta 15

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

• ATP is formed in glycolysis by • substrate-level phosphorylation • during which

–  an enzyme transfers a phosphate group from a substrate molecule to ADP and

–  ATP is formed. • two NADH molecules are produced for each initial glucose

molecule and • ATP molecules are generated.

• The compounds that form between the initial reactant, glucose, and the final product, pyruvate, are called intermediates.

Substrate Level Phosphorylation

Enzyme Enzyme

P

P

ADP

P

ATP

Substrate Product

Pyruvate is chemically processed to enter the citric acid cycle

–  A large, multienzyme complex catalyzes three reactions in the mitochondrial matrix

•  A carbon atom is removed from pyruvate and released in CO2

•  The remaining two-carbon compound is oxidized,

•  molecule of NAD+ is reduced to NADH •  Coenzyme A joins with the 2-carbon group to

produce acetyl CoA

From Glycolysis to Citric Acid Cycle Making Acetyl CoA

Pyruvate

Coenzyme A

Acetyl coenzyme A

NAD+ NADH H+

CoA

CO2 3

2

1

The citric acid cycle

• The citric acid cycle –  is also called the Krebs cycle (after the German-

British researcher Hans Krebs, who worked out much of this pathway in the 1930s),

• Citric acid cycle processes two molecules of acetyl CoA for each initial glucose.

• Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is –  2 ATP, –  6 NADH and –  2 FADH2.

Acetyl CoA

Citric Acid Cycle

CoA CoA

CO2 2

3

3

NAD+

3 H+

NADH

ADP ATP P

FAD

FADH2

Bioenergetics

Sengupta 16

Figure 6.9B_s1 CoA

CoA

1

Acetyl CoA

Oxaloacetate

Citric Acid Cycle

2 carbons enter cycle

Step Acetyl CoA stokes the furnace.

1

Figure 6.9B_s2

NADH

NADH

NAD+

NAD+

H+

H+

CO2

CO2

ATP ADP P

CoA CoA

3 2 1

3

1

2

Acetyl CoA

Oxaloacetate

Citric Acid Cycle

2 carbons enter cycle

Citrate

leaves cycle

Alpha-ketoglutarate

leaves cycle

Step Acetyl CoA stokes the furnace.

Steps – NADH, ATP, and CO2 are generated during redox reactions.

Figure 6.9B_s3

NADH

NADH

NAD+

NAD+ NAD+ NADH

H+

H+

H+

CO2

CO2

ATP ADP P

FAD

FADH2

CoA CoA

3 2 1 4 5

3 4

5

1

2

Acetyl CoA

Oxaloacetate

Citric Acid Cycle

2 carbons enter cycle

Citrate

leaves cycle

Alpha-ketoglutarate

leaves cycle

Succinate

Malate

Step Acetyl CoA stokes the furnace.

Steps – NADH, ATP, and CO2 are generated during redox reactions.

Steps – Further redox reactions generate FADH2 and more NADH.

3 NAD+

ADP + P

3 NADH

FADH2 FAD

Acetic acid

Citric acid

Acceptor molecule

Citric Acid Cycle

ATP

2 CO2

INPUT OUTPUT

Phase 3: Oxidative phosphorylation

•  Occurs in the cristae of mitochondria

•  The molecules of the electron transport chain are built into the inner membranes of mitochondria.

•  Uses the energy released by electrons “falling” down the electron transport chain to pump H+ across a membrane

•  Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP

–  These ions store potential energy.

–  requires an adequate supply of oxygen.

Making ATP in Bulk

• Electrons from NADH and FADH2 travel down the electron transport chain to O2.

• Oxygen picks up H+ to form water.

• Energy released by these redox reactions is used to pump H+ from the mitochondrial matrix into the intermembrane space.

• In chemiosmosis, the H+ diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP.

Bioenergetics

Sengupta 17

The Electron Transport Chain

Oxidative Phosphorylation

Electron Transport Chain Chemiosmosis

Mito- chondrial matrix

Inner mito- chondrial membrane

Intermem- brane space

Electron flow

Protein complex of electron carriers

Mobile electron carriers ATP

synthase

NADH NAD+ 2 H+ FADH2 FAD

O2 H2O

ADP P ATP

1 2

H+

H+

H+

H+

H+ H+

H+

H+

H+ H+

H+

I

II

III IV

Oxidative Phosphorylation

H+

H+

H+ H+

H+

H+

H+ H+

H+

H+

H+

Oxidative Phosphorylation

Electron Transport Chain Chemiosmosis

I

II

IIIIV

NADH NAD+ 2 H+ FADH2 FAD

O2 H2O

ADP P ATP

2 1

Electron flow

Protein complex of electron carriers

Mobile electron carriers ATP

synthase

ATP synthase

http://www.mrc-mbu.cam.ac.uk/research/atp-synthase

• ATP synthase is a huge molecular complex (>500,000 daltons) embedded in the inner membrane of mitochondria. • Its function is to convert the energy of protons (H+) moving down their concentration gradient into the synthesis of ATP. • 3 to 4 protons moving through this machine is enough to convert a molecule of ADP and Pi (inorganic phosphate) into a molecule of ATP. • One ATP synthase complex can generate >100 molecules of ATP each second. http://mm.rcsb.org

Interrupting cellular respiration can have both harmful and beneficial effects

Three categories of cellular poisons obstruct the process of oxidative phosphorylation. These poisons

1. block the electron transport chain (for example, rotenone, cyanide, and carbon monoxide),

2. inhibit ATP synthase (for example, the antibiotic oligomycin), or

3. make the membrane leaky to hydrogen ions (called uncouplers, examples include dinitrophenol).

Poisons of the Cellular Respiration

ATP synthase

NAD+ NADH

FADH2 FAD

H+

H+ H+

H+

H+ H+ H+ H+

2 H+

H2O ADP ATP P

O2 2 1

Rotenone Cyanide, carbon monoxide

Oligomycin

DNP

Review: Each molecule of glucose yields many molecules of ATP

• The total yield is about 32 ATP molecules per glucose molecule.

• This is about 34% of the potential energy of a glucose molecule.

• In addition, water and CO2 are produced.

Bioenergetics

Sengupta 18

The overview of cellular respiration

NADH High-energy electrons

carried by NADH

GLYCOLYSIS Glucose Pyruvate

Cytoplasm

ATP Substrate-level phosphorylation

Substrate-level phosphorylation

CITRIC ACID CYCLE

CO2 CO2

ATP

NADH FADH2 and

ATP

Mitochondrion

Oxidative phosphorylation

OXIDATIVE PHOSPHORYLATION

(Electron Transport and Chemiosmosis)

Energy Harvest

2 ATP

2 ATP

34 ATP

glycolysis

38 ATP maximum per glucose molecule

Krebs cycle

electron transport

chain

glucose

(b) In schematic terms

(a) In metaphorical terms

mitochondrion H2O

O2

2 FADH2

2 NADH

2 NADH

6 NADH CO2

CO2 glucose derivatives

cytosol

glycolysis

Krebs cycle

electron transport

chain

insert 1 glucose

2 energy tokens

2 energy tokens

32 energy tokens

reactants products

The Energy Harvest

Each molecule of glucose yields many molecules of ATP

–  Glycolysis and the citric acid cycle together yield four ATP per glucose molecule

–  Oxidative phosphorylation, using electron transport and chemiosmosis, yields 34 ATP per glucose

–  These numbers are maximum –  Some cells may lose a few ATP to NAD+ or FAD

shuttles

FERMENTATION: ANAEROBIC HARVESTING OF ENERGY

Fermentation enables cells to produce ATP without oxygen

• Fermentation is a way of harvesting chemical energy that does not require oxygen. Fermentation –  takes advantage of glycolysis, –  produces two ATP molecules per glucose, and –  reduces NAD+ to NADH.

• The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD+.

Fermentation enables cells to produce ATP without oxygen

• Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation, in which –  NADH is oxidized to NAD+ and –  pyruvate is reduced to lactate.

Bioenergetics

Sengupta 19

Fermentation enables cells to make ATP without oxygen

• Lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells.

• The dairy industry uses lactic acid fermentation by bacteria to make cheese and yogurt.

• Other types of microbial fermentation turn –  soybeans into soy sauce and –  cabbage into sauerkraut.

Lactic acid Fermentation

2 NAD+

2 NADH

2 NAD+

2 NADH

2 Lactate

2 Pyruvate

Glucose

2 ADP

2 ATP

2 P

Gly

coly

sis

Alcohol Fermentation

• The baking and winemaking industries have used alcohol fermentation for thousands of years.

• In this process yeasts (single-celled fungi) –  oxidize NADH back to NAD+ and –  convert pyruvate to CO2 and ethanol.

Alcohol Fermentation

2 NAD+

2 NADH

2 NAD+

2 NADH

2 Ethanol

2 Pyruvate

Glucose

2 ADP

2 ATP

2 P

Gly

coly

sis

2 CO2

Food

Polysaccharides Fats Proteins

Sugars Glycerol Fatty acids Amino acids

Glycolysis Acetyl CoA

Citric Acid Cycle

Electron Transport

ATP

Figure 6.UN02

cellular work

chemiosmosis

H+ gradient

glucose and organic fuels

Cellular respiration

generates has three stages oxidizes uses

produce some

produces many

to pull electrons down

H+ diffuse through

ATP synthase

pumps H+ to create uses

uses by a process called

energy for

(a)

(b)

(c)

(d)

(e)

(f) (g)

to