Chapter 6 How cells harvest chemical energy Musebio101 summer 2010

Chapter 6How cells harvest chemical energy

Musebio101summer 2010

Photosynthesis and cellular respiration provide energy for life

• Energy is necessary for life processes– These include growth, transport, manufacture,

movement, reproduction, and others– Energy that supports life on Earth is captured from

sun rays reaching Earth through plant, algae, protist, and bacterial photosynthesis

Sunlight energy

ECOSYSTEM

Photosynthesisin chloroplasts

Glucose

Cellular respirationin mitochondria

H2O

CO2

O2

(for cellular work)

ATP

Heat energy

Cellular respiration banks energy in ATP molecules

• Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to ATP– Cellular respiration produces 38 ATP molecules from

each glucose molecule

– Other foods (organic molecules) can be used as a source of energy as well

Introduction to Metabolism

• Cells break down organic molecules to obtain energy– Used to generate ATP

• Most energy production takes place in mitochondria

Metabolism• Metabolism – refers to all chemical reaction

occurring in body– Catabolism – break down complex molecules

• Exergonic – produce more energy than they consume

– Anabolism – combine simple molecules into complex ones

• Endergonic – consume more energy than they produce

• Adenosine triphosphate (ATP)– “energy currency”– ADP + P + energy ↔ ATP

Reactants

Amount ofenergy

released

Po

ten

tia

l en

erg

y o

f m

ole

cu

les

Energy released

Products

Metabolism• Catabolism

– Is the breakdown of organic substrates

– Releases energy used to synthesize high-energy

compounds (e.g., ATP)

• Anabolism

– Is the synthesis of new organic molecules

C6H12O6 + 6 O2

Glucose Oxygen

6 CO2

Carbondioxide

+ 6 H2O

Water

+ ATPs

Energy

Cellular respiration is a catabolic reaction

Energy conversion in a cell

Energy for cellular work

Cellular respiration

Heat

Glucose

Oxygen Water

Carbon dioxide

Fuel Energy conversion Waste products

Energy fromexergonicreactions

Energy forendergonicreactions

Role of ATP in linking anabolic and catabolic reactions

Ribose

Adenine

Triphosphate (ATP)Adenosine

Phosphategroup

Hydrolysis

Diphosphate (ADP)Adenosine

Carbohydrate Metabolism

• Mitochondrial Membranes

– Outer membrane

• Contains large-diameter pores

• Permeable to ions and small organic molecules (pyruvic acid)

– Inner membrane

• Contains carrier protein

• Moves pyruvic acid into mitochondrial matrix

– Intermembrane space

• Separates outer and inner membranes

Figure 24.5

Via oxidativephosphorylationVia substrate-level

phosphorylation

MitochondrionMitochondrialcristae

Cytosol

KrebscycleGlucose

GlycolysisPyruvicacid

Electron transportchain and oxidativephosphorylation

Chemical energy (high-energy electrons)

1 During glycolysis, each glucose molecule is broken down into two molecules of pyruvic acid in the cytosol.

2 The pyruvic acid then enters the mitochondrial matrix, where the Krebs cycle decomposes it to CO2. During glycolysis and the Krebs cycle, small amounts of ATP are formed by substrate-level phosphorylation.

3 Energy-rich electrons picked up bycoenzymes are transferred to the electron transport chain, built into the cristae membrane. The electron transport chain carries out oxidative phosphorylation, which accounts for most of the ATP generated by cellular respiration.

Chemical energy

Cellular respiration begins with glycolysis


• Glucose Breakdown– Occurs in small steps

• Which release energy to convert ADP to ATP

– One molecule of glucose nets 36 molecules of ATP

– Glycolysis • Breaks down glucose in cytosol into smaller molecules used by

mitochondria

• Does not require oxygen: anaerobic reaction

– Aerobic Reactions• Also called aerobic metabolism or cellular respiration

• Occur in mitochondria, consume oxygen, and produce ATP

Enzyme

CatalysisEnzyme

(a) Substrate-level phosphorylation

Steps – ATP and pyruvateare produced.

Step A redox reactiongenerates NADH.

Step A six-carbon intermediate splitsInto two three-carbon intermediates.

Steps – A fuel molecule is energized,using ATP.

ENERGY INVESTMENTPHASEGlucose

Glucose-6-phosphate

1

Fructose-6-phosphate

Step

ADP

ATP

P

3

ADP

ATP

P

2

P

4

P Fructose-1,6-bisphosphate

5 5

PP

P

P

P

P

NAD+

PP

ENERGY PAYOFF PHASE

Glyceraldehyde-3-phosphate(G3P)

1,3-Bisphosphoglycerate

NADH

NAD+

NADH

+ H+ + H+

ADP ADP

ATP ATP6 6

3-Phosphoglycerate

2-Phosphoglycerate

7 7

8 8

P P

P P

P P

H2O H2O

ADP ADP

ATP ATP

9 9

Phosphoenolpyruvate(PEP)

Pyruvate

1 3

4

5

6 9

Substrate level phosphorylation energy payout phase.

ADP

O

Glucose (1 molecule)

CH2OH

OH

OH

OH4 1

3 2

5

6

ATP

H H

H

HHO

1

H

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OHOH

OH

OH2CP

ATP

H

HO

H

H

HH

H

H

H

HO

1

2

H

H

Phosphofructokinase

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OH

OH

OH

CH2OH

Fructose 6-phosphate

O

OH

H

OH2C6

5

4 3

2

1

ADP

P

OH2CP

ATP

ATP

OH

H

HO

H

H

HH

H H

H

H

HO

H

HO

1

2

3

H

H

Phosphofructokinase

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OH

OH

OH

CH2OH


O

OH

H

OH2C6

5

4 3

2

1

CH2O

Fructose 1, 6-bisphosphate

O

OH

H

OH2CADP

PP

P

OH2CP

ATP

ATP

OH

H

HO

H

H

HH

H

H

H

H

H

H

HO

HO

H

HO

OH

1

2

3

4

H

H

Phosphofructokinase

Dihydroxyacetonephosphate

CH2OH

CH2OC O

Glyceraldehyde3-phosphate

HCOHCH2O

OHC

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OH

OH

OH

CH2OH


O

OH

H

OH2C6

5

4 3

2

1

CH2O


O

OH

H

OH2CADP

PP

P

P

P

OH2CP

ATP

ATP

OH

H

HO

H

H

HH

H

H

H

H

H

H

HO

HO

H

HO

OH

1

2

3

4

5

H

H

+ 2H+NADH

HCOHC

CH2O

OO 1, 3-Bisphosphoglyceric acid

(2 molecules)

2

P

P

Phosphofructokinase


CH2OH

CH2OC O


HCOHCH2O

OHC

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OH

OH

OH

CH2OH


O

OH

H

OH2C6

5

4 3

2

1

CH2O


O

OH

H

OH2CADP

PP

P

P

P

OH2CP

ATP

ATP

OH

H

HO

H

H

HH

H

H

H

H

H

H

HO

HO

H

HO

OH

1

2

3

4

5

6

H

H

2 NAD++ 2 P

+ 2H+NADH

HCOHC

CH2O

O

COOH

O

2

2 ADP

HCOHCH2O

1, 3-Bisphosphoglyceric acid(2 molecules)

2

3-Phosphoglyceric acid(2 molecules)

P

P

P

Phosphofructokinase


CH2OH

CH2OC O


HCOHCH2O

OHC

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OH

OH

OH

CH2OH


O

OH

H

OH2C6

5

4 3

2

1

CH2O


O

OH

H

OH2CADP

PP

P

P

P

OH2CP

ATP

ATP

ATP

OH

H

HO

H

H

HH

H

H

H

H

H

H

HO

HO

H

HO

OH

1

2

3

4

5

6

7H

H

2 NAD++ 2 P

+ 2H+NADH

HCOHC

CH2O

O

COOH

O

2

2 ADP

HCOHCH2O


2


COOH

CH2OHHCO 2-Phosphoglyceric acid

(2 molecules)P

P

P

P

Phosphofructokinase


CH2OH

CH2OC O


HCOHCH2O

OHC

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OH

OH

OH

CH2OH


O

OH

H

OH2C6

5

4 3

2

1

CH2O


O

OH

H

OH2CADP

PP

P

P

P

OH2CP

ATP

ATP

ATP

OH

H

HO

H

H

HH

H

H

H

H

H

H

HO

HO

H

HO

OH

1

2

3

4

5

6

7

8

H

H

2 NAD++ 2 P

+ 2H+NADH

HCOHC

CH2O

O

COOH

O

2

2 ADP

HCOHCH2O


2


COOH


(2 molecules)

COOH

CH2

C O Phosphoenolpyruvic acid(2 molecules)

P

P

P

P

P

Phosphofructokinase


CH2OH

CH2OC O


HCOHCH2O

OHC

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OH

OH

OH

CH2OH


O

OH

H

OH2C6

5

4 3

2

1

CH2O


O

OH

H

OH2CADP

PP

P

P

P

OH2CP

ATP

ATP

ATP

OH

H

HO

H

H

HH

H

H

H

H

H

H

HO

HO

H

HO

OH

1

2

3

4

5

6

7

8

9

H

H

2 NAD++ 2 P

+ 2H+NADH

2 NAD++ 2

HCOHC

CH2O

O

COOH

O

2

2 ADP

P

HCOHCH2O


2


COOH


(2 molecules)

Pyruvic acid(2 molecules)

COOH

CH2

2

2 ADP

C O Phosphoenolpyruvic acid(2 molecules)

COOH

CH3

C O

P

P

P

P

P

Phosphofructokinase


CH2OH

CH2OC O


HCOHCH2O

OHC

ADP

O


CH2OH

OH

OH

OH4 1

3 2

5

6

Glucose 6-phosphate

O

OH

OH

OH

CH2OH


O

OH

H

OH2C6

5

4 3

2

1

CH2O


O

OH

H

OH2CADP

PP

P

P

P

OH2CP

ATP

ATP

ATP

ATP

OH

H

HO

H

H

HH

H

H

H

H

H

H

HO

HO

H

HO

OH

1

2

3

4

5

6

7

8

9

10

H

H

Fate of pyruvic acid

2 ADP

P

ATP2 GL

YC

OL

YS

IS

NADH

NAD+

2

2

NADH2

NAD+2

2 Pyruvate

2 Ethanol

Alcohol fermentation

Glucose

CO22

released

2

Glycolysis evolved early in the history of life on Earth

• Glycolysis is the universal energy-harvesting process of living organisms– So, all cells can use glycolysis for the energy

necessary for viability– The fact that glycolysis has such a widespread

distribution is good evidence for evolution

Carbohydrate Metabolism • Oxidation and Reduction

– Oxidation (loss of electrons)• Electron donor is oxidized

– Reduction (gain of electrons)• Electron recipient is reduced

– The two reactions are always paired

Energy transfer

• Oxidation-reduction or redox reactions– Oxidation – removal of electrons

• Decrease in potential energy• Dehydrogenation – removal of hydrogens• Liberated hydrogen transferred by coenzymes

– Nicotinamide adenine dinucleotide (NAD)– Flavin adenine dinucleotide (FAD)

• Glucose is oxidized

– Reduction – addition of electrons• Increase in potential energy


• The TCA Cycle (citric acid cycle)

– The function of the citric acid cycle is

• To remove hydrogen atoms from organic molecules and transfer

them to coenzymes

– In the mitochondrion

• Pyruvic acid reacts with NAD and coenzyme A (CoA)

• Producing 1 CO2, 1 NADH, 1 acetyl-CoA

– Acetyl group transfers

• From acetyl-CoA to oxaloacetic acid

• Produces citric acid

CITRIC ACID CYCLE

NAD+

NADH

3 H+

CO2

3

3

2

CoA

CoA

Acetyl CoA

PADP +ATP

FADH2

FAD

Krebs cycle

NAD+

NAD+

GDP +

NAD+

FAD

NAD+

NADH+H+

Cytosol

Mitochondrion(matrix)

NADH+H+

FADH2

NADH+H+

Citric acid(initial reactant)

Isocitric acid

Oxaloacetic acid (pickup molecule)

Malic acid

Succinic acidSuccinyl-CoA

GTP

ADP

Carbon atomInorganic phosphateCoenzyme A

Acetyl CoA

Pyruvic acid from glycolysis

Transitionalphase

Fumaric acid

NADH+H+

CO2

CO2

CO2

-Ketoglutaric acid

Electron trans-port chain and oxidativephosphorylation

Glycolysis Krebscycle

Carbohydrate Metabolism • The TCA Cycle

– CoA is released to bind another acetyl group

– One TCA cycle removes two carbon atoms• Regenerating 4-carbon chain

– Several steps involve more than one reaction or enzyme

– H2O molecules are tied up in two steps

– CO2 is a waste product

– The product of one TCA cycle is• One molecule of GTP (guanosine triphosphate)

The Krebs Cycle

1

CCH2

COOHO

Oxaloacetic acid

COOHCitric acid

H2CCOOHCOOHHOC

H2CCOOH

+ H+Pyruvic

acidAcetyl

coenzyme A

CCH3

OCH3

CCOOH

O

To electrontransport chain

H2O

CO2

NAD+

KREBSCYCLE

NADH

CoA

CoA

1

CCH2

COOHO

Oxaloacetic acid

COOH

Isocitric acid

H2CCOOH

HOCCOOHHCCOOH

H

Citric acid

H2CCOOHCOOHHOC

H2CCOOH

+ H+Pyruvic

acidAcetyl

coenzyme A

CCH3

OCH3

CCOOH

O


H2O

CO2

NAD+

KREBSCYCLE

NADH

CoA

CoA

2

1


CO2

+ H+

CCH2

COOHO

Oxaloacetic acid

COOH

Alpha-ketoglutaric acid

H2CCOOHHCH

C COOH

Isocitric acid

H2CCOOH

HOCCOOHHCCOOH

H

Citric acid

H2CCOOHCOOHHOC

H2CCOOH

NAD+

+ H+Pyruvic

acidAcetyl

coenzyme A

CCH3

OCH3

CCOOH

O


H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

CoA

CoA

2

3

O

1


CO2

+ H+NADH

CO2

+ H+

CCH2

COOHO

Oxaloacetic acid

COOH

Succinyl CoA

H2CCOOHCH2

C S CoA Alpha-ketoglutaric acid

H2CCOOHHCH

C COOH

Isocitric acid

H2CCOOH

HOCCOOHHCCOOH

H

Citric acid

H2CCOOHCOOHHOC

H2CCOOH

NAD+

NAD+

+ H+Pyruvic

acidAcetyl

coenzyme A

CCH3

OCH3

CCOOH

O


H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

O

CoA

O

CoA

2

3

4

1


CO2

+ H+NADH

CO2

+ H+

CCH2

COOHO

Oxaloacetic acid

COOH

H2CCOOHH2CCOOHSuccinic acid

Succinyl CoA

H2CCOOHCH2


H2CCOOHHCH

C COOH

Isocitric acid

H2CCOOH

HOCCOOHHCCOOH

H

Citric acid

H2CCOOHCOOHHOC

H2CCOOH

NAD+

NAD+

GDP

+ H+Pyruvic

acidAcetyl

coenzyme A

CCH3

OCH3

CCOOH

O


ADP

H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

ATP

GTP

O

CoA

CoA

O

CoA

2

3

4

5

1


CO2

+ H+NADH

CO2

+ H+

To electrontransportchain

CCH2

COOHO

Oxaloacetic acid

COOH


Succinyl CoA

H2CCOOHCH2


H2CCOOHHCH

C COOH

Isocitric acid

H2CCOOH

HOCCOOHHCCOOH

H

Citric acid

H2CCOOHCOOHHOC

H2CCOOH

Fumaric acid

NAD+

NAD+

GDP

FAD

HCCH

+ H+Pyruvic

acidAcetyl

coenzyme A

CCH3

OCH3

CCOOH

O


ADP

FADH2

COOH

COOH

H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

ATP

GTP

CoA

CoA

O

CoA

2

3

4

5

6

O

1


CO2

+ H+NADH

CO2

+ H+


CCH2

COOHO

Oxaloacetic acid

COOH

HCOHCH2

COOH

COOH


Malic acid

Succinyl CoA

H2CCOOHCH2


H2CCOOHHCH

C COOH

Isocitric acid

H2CCOOH

HOCCOOHHCCOOH

H

Citric acid

H2CCOOHCOOHHOC

H2CCOOH

Fumaric acid

NAD+

NAD+

GDP

FAD

HCCH

+ H+Pyruvic

acidAcetyl

coenzyme A

CCH3

OCH3

CCOOH

O


ADP

FADH2

COOH

COOH

H2O

H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

ATP

GTP

CoA

CoA

O

CoA

2

3

4

5

6

7

O

1


CO2

+ H+NADH

CO2

+ H+


CCH2

COOHO

Oxaloacetic acid

COOH

+ H+NADH

HCOHCH2

COOH

COOH


Malic acid

Succinyl CoA

H2CCOOHCH2


H2CCOOHHCH

C COOH

Isocitric acid

H2CCOOH

HOCCOOHHCCOOH

H

Citric acid

H2CCOOHCOOHHOC

H2CCOOH

Fumaric acid

NAD+

NAD+

GDP

FAD

NAD+

HCCH

+ H+Pyruvic

acidAcetyl

coenzyme A

CCH3

OCH3

CCOOH

O


ADP

FADH2

COOH

COOH

H2O

H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

ATP

GTP

CoA

CoA

O

CoA

2

3

4

5

6

7

8

O


A Summary of the Energy Yield of Aerobic Metabolism.


• Summary: The TCA Cycle (Krebs cycle)CH3CO - CoA + 3NAD + FAD + GDP + Pi + 2 H2O

CoA + 2 CO2 + 3NADH + FADH2 + 2 H+ + GTP


• The Electron Transport System (ETS)– Is the key reaction in oxidative phosphorylation– Is in inner mitochondrial membrane– Electrons carry chemical energy

• Within a series of integral and peripheral proteins


• Coenzyme FAD

– Accepts two hydrogen atoms from TCA cycle:

• Gaining two electrons

• Coenzyme NAD

– Accepts two hydrogen atoms

– Gains two electrons

– Releases one proton

– Forms NADH + H+

1NADH+ 2 H+

GLYCOLYSIS2

2

2 Pyruvic acid

1 Glucose

ATP1NADH+ 2 H+

GLYCOLYSIS

+ 2 H+NADH

CO2FORMATIONOF ACETYLCOENZYME A

2

2

2

2

2 Acetylcoenzyme A

2 Pyruvic acid

1 Glucose

ATP

2

1NADH+ 2 H+

GLYCOLYSIS

+ 2 H+NADH


KREBSCYCLE

+ 6 H+

CO2

FADH2

NADH

2

4

6

2

2

2

2

2

2 Acetylcoenzyme A

2 Pyruvic acid

1 Glucose

ATP

ATP

2

3

1NADH+ 2 H+

GLYCOLYSIS

+ 2 H+NADH


KREBSCYCLE

+ 6 H+

CO2

FADH2

NADH

2

4

6

2

ELECTRONTRANSPORTCHAIN

e–

e–

e–

32 or 34

O26

6

2

2

2

2

H2O

Electrons

2 Acetylcoenzyme A

2 Pyruvic acid

1 Glucose

ATP

ATP ATP

2

3

4

ATPNAD+

NADH

H+

H+2e–

2e–

Electron transport

chain

Controlledrelease ofenergy forsynthesis

of ATP

+

O2

H2O

12


Oxidative Phosphorylation.

Glycolysis Krebscycle

Electron trans-port chain and oxidativephosphorylation

EnzymeComplex I

EnzymeComplex III

EnzymeComplex IV

EnzymeComplex II

NADH+H+

FADH2

Fre

e e

nerg

y r

ela

tive t

o O

2 (

kcal/

mol)

The actions of the three proton pumps and ATP synthase in the inner membrane of mitochondria

Space between outerand inner mitochondrialmembranes

Innermito-chondrialmembrane

Mitochondrialmatrix

H+ channel

NADH dehydrogenasecomplex: FMN andfive Fe-S centers

Cytochrome b-c1

complex: cyt b, cyt c1, and an Fe-S center

Cytochrome oxidasecomplex: cyt a, cyt a3,and two Cu

NAD1 1/2O2

e–

e–

e–

e–

e–

H+ H+H+

+ + + + + + +

– – – – – – –

H2O

Q

Cyt c

NADH+ H+ H+

3ADP +

ATP synthase

PATP

1 2 3

3

ADP +

Membrane

High H+ concentration inintermembrane space

Low H+ concentration in mitochondrial matrix

Energyfrom food

Protonpumps

(electrontransport

chain)ATPsynthase

(b) Oxidative phosphorylation

Stage 1 Digestion in GI tract lumen to absorbable forms.Transport via blood totissue cells.

Stage 2 Anabolism (incorporation into molecules) and catabolism of nutrients to form intermediates within tissue cells.

Stage 3 Oxidative breakdown of products of stage 2 in mitochondria of tissue cells. CO2 is liberated, and H atoms removed are ultimately delivered to molecular oxygen, formingwater. Some energy released isused to form ATP.

Glycogen

PROTEINS

Proteins Fats

CARBOHYDRATES

Glucose

FATS

Amino acidsGlucose and other sugarsGlycerol Fatty acids

Pyruvic acid

Acetyl CoA

Infrequent CO2

NH3

H

Krebscycle

Oxidativephosphorylation

(in electron transport chain)

O2

H2O

Overview of metabolic processes

Summary of cellular respiration

Via oxidativephosphorylationVia substrate-level

phosphorylation

MitochondrionMitochondrialcristae

Cytosol

KrebscycleGlucose

GlycolysisPyruvicacid

Electron transportchain and oxidativephosphorylation

Chemical energy (high-energy electrons)

1 During glycolysis, each glucose molecule is broken down into two molecules of pyruvic acid in the cytosol.

2 The pyruvic acid then enters the mitochondrial matrix, where the Krebs cycle decomposes it to CO2. During glycolysis and the Krebs cycle, small amounts of ATP are formed by substrate-level phosphorylation.

3 Energy-rich electrons picked up bycoenzymes are transferred to the elec-tron transport chain, built into the cristae membrane. The electron transport chain carries out oxidative phosphorylation, which accounts for most of the ATP generated by cellular respiration.

Chemical energy

Food, such aspeanuts

ProteinsFatsCarbohydrates

Glucose

OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)

CITRICACID

CYCLE

AcetylCoA

GLYCOLYSIS

Pyruvate

Amino acidsGlycerolSugars Fatty acids

Amino groups

G3P

ATP

Review• Energy is harvested from high energy glucose by the

mitochondria

• The process begins in the cytoplasm with glycolysis where glucose is converted to pyruvate

• The TCA cycle (Krebs cycle) harvests energy from the pyruvate and stores it as reduced electron carrier molecules

• The carrier molecules cash in these electrons for ATP in the electron transport chain if oxygen is available

Review (cont)

• 2 net ATP are made from each glucose in glycolysis

• 34 additional ATP are made from each glucose if oxygen is available to help run the TCA cycle and electron transport chain

Documents

Chapter 6 How cells harvest chemical energy Musebio101 summer 2010