CELLULAR RESPIRATION Chapter 1 Electron transport chain and chemiosmosis Mitochondrion Citric acid...

CELLULAR RESPIRATION

Chapter 1

Electron transportchain andchemiosmosis

Mitochondrion

Citric acid cycle

Preparatory reaction

2 32 ADPor 34

32or 34

2

4 ATP total

net gain

2 ADP

NADH

NADH andFADH2

Glycolysis

NADH

glucose pyruvate

Cytoplasm

e–

e–

e–

e–

e–

e–

e–

2 ADP

4 ADP

ATP 2 ADP ATP ATP

Outline

Cellular Respiration Phases of Cellular Respiration

Glycolysis Preparatory Reaction Citric Acid Cycle Electron Transport System Fermentation

Overview

Living cells require energy from outside sources

Some animals, such as the giant panda, obtain energy by eating plants, and some animals feed on other organisms that eat plants

How do these leaves power the work of life for the giant panda?

Lightenergy

ECOSYSTEM

Photosynthesis in chloroplasts

CO2 + H2O Cellular

respirationin mitochondria

Organicmolecule

s

+ O2

ATP powers most cellular work

Heatenergy

ATP

Cellular Respiration

A cellular process that breaks down carbohydrates and other metabolites with the connected buildup of ATP

Breakdown of organic molecules is exergonic

Other metabolites? i.e.

ADP + P ATP

intermembranespacecristae

CO2

H2O

glucosefrom

O2fromair

O2 and glucose enter cells,which release H2O and CO2.

Mitochondria useenergy fromglucose to form ATPfrom ADP + P .

Cellular Respiration: Processes Several processes are central to

cellular respiration and related pathways Aerobic respiration consumes organic

molecules and O2 and yields ATP

Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2

Fermentation is a partial degradation of sugars that occurs without necessary usage of O2

Cellular Respiration: Processes

Most prevalent and efficient is aerobic process.

C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat)

Energy extracted from glucose molecule: Released step-wise

Allows ATP to be produced efficiently

Oxidation-reduction enzymes include NAD+ and FAD as coenzymes

Redox Reactions: Oxidation and Reduction

The transfer of electrons during chemical reactions releases energy stored in organic molecules

This released energy is ultimately used to synthesize ATPbecomes

oxidized(loses electron)

becomes reduced

(gains electron)

Reactantsbecomes oxidized

becomes reduced

Products

Methane

(reducing

agent)

Oxygen(oxidizin

gagent)

Carbon dioxide

Water

Redox Reactions and Aerobic Cellular Respiration Electrons are removed from substrates

and received by oxygen, which combines with H+ to become water.

Glucose is oxidized and O2 is reduced becomes oxidized

becomes reduced

Step-wise Energy Harvest: NAD+

Step-wise reaction for energy harvest

Electrons from organic compounds are usually first transferred to NAD+, a coenzyme

As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration

Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP

Step-wise Energy Harvest: NAD+

NADH passes the electrons to the electron transport chain

Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction

O2 pulls electrons down the chain in an energy-yielding tumble

The energy yielded is used to regenerate ATP

Fre

e

en

erg

y, G

Fre

e

en

erg

y, G

(a) Uncontrolled reaction

H2

O

H2 + 1/2 O2

Explosiverelease ofheat and

lightenergy

(b) Cellular respiration

Controlledrelease ofenergy forsynthesis

ofATP

2 H+ + 2 e–

2 H

+ 1/2

O2(from food via NADH)

ATP

ATPATP

1/2

O2

2 H+

2 e–Ele

ctron

transp

ort

chain

H2

O

Stages of Cellular Respiration Cellular respiration has four stages:

Glycolysis (breaks down glucose into two molecules of pyruvate)

Transition (preparatory) (pyruvates are oxidized and enter mitochondria)

The citric acid cycle (completes the breakdown of glucose)

Oxidative phosphorylation: Electron Transport Chain and chemiosis (accounts for most of the ATP synthesis)

Mitochondrion

Substrate-levelphosphorylatio

n

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH

Substrate-levelphosphorylatio

n

ATP

Electrons carried

via NADH andFADH2

Oxidativephosphorylatio

n

ATP

Citricacidcycle

Oxidativephosphorylation

:electron transport

andchemiosmosis

STAGE 1: Glycolysis Pathway: Splitting of Sugars Glycolysis (“splitting of sugar”) breaks

down glucose into two molecules of pyruvate

Occurs in the cytoplasm and has two major phases: Energy investment phase Energy payoff phase

Fig. 9-9-1

ATP

ADP

Hexokinase1

ATP

ADP

Hexokinase

1

Glucose

Glucose-6-phosphate

Glucose

Glucose-6-phosphate

Fig. 9-9-2

Hexokinase

ATP

ADP

1

Phosphoglucoisomerase

2

Phosphogluco-isomerase

2

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Glucose-6-phosphate

Fructose-6-phosphate

1

Fig. 9-9-3

Hexokinase

ATP

ADP

Phosphoglucoisomerase

Phosphofructokinase

ATP

ADP

2

3

ATP

ADP

Phosphofructo-kinase

Fructose-1, 6-

bisphosphate

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Fructose-1, 6-

bisphosphate

1

2

3

Fructose-6-phosphate

3

Fig. 9-9-4

Glucose

ATP

ADP

Hexokinase

Glucose-6-phosphate

Phosphoglucoisomerase

Fructose-6-phosphate

ATP

ADP

Phosphofructokinase

Fructose-1, 6-

bisphosphate

Aldolase

Isomerase

Dihydroxyacetone

phosphate

Glyceraldehyde-

3-phosphate

1

2

3

4

5

Aldolase

Isomerase

Fructose-1, 6-

bisphosphate

Dihydroxyacetone

phosphate

Glyceraldehyde-

3-phosphate

4

5

Fig. 9-9-52 NAD+

NADH

2

+ 2 H+

2

2Pi

Triose phosphatedehydrogenase

1, 3-Bisphosphoglycerate

6

2 NAD+

Glyceraldehyde-

3-phosphate

Phosphoglyceraldehydedehydrogenase

NADH

2

+ 2 H+

2 P i

1, 3-Bisphosphoglycerate

6

2

2

Fig. 9-9-62 NAD+

NADH

2

Triose phosphatedehydrogenase

+ 2 H+

2 P i

2

2 ADP

1, 3-Bisphosphoglycerate

Phosphoglycerokinase2

ATP

2 3-Phosphoglycerate

6

7

2

2 ADP

2 ATP

1, 3-Bisphosphoglycerate

3-Phosphoglycerate

Phosphoglycero-kinase

2

7

Fig. 9-9-7

3-Phosphoglycerate

Triose phosphatedehydrogenase

2 NAD+

2 NADH+ 2 H+

2 P i

2

2 ADP

Phosphoglycerokinase

1, 3-Bisphosphoglycerate

2 ATP

3-Phosphoglycerate

2

Phosphoglyceromutase

2-Phosphoglycerate

2

2-Phosphoglycerate

2

2

Phosphoglycero-mutase

6

7

8

8

Fig. 9-9-82 NAD+

NADH

2

2

2

2

2

+ 2 H+

Triose phosphatedehydrogenase

2 P i

1, 3-Bisphosphoglycerate

Phosphoglycerokinase

2 ADP

2 ATP

3-Phosphoglycerate

Phosphoglyceromutase

Enolase

2-Phosphoglycerate

2 H2O

Phosphoenolpyruvate

9

8

7

6

2 2-Phosphoglycerate

Enolase

2

2 H2O

Phosphoenolpyruvate

9

Fig. 9-9-9

Triose phosphatedehydrogenase

2 NAD+

NADH

2

2

2

2

2

2

2 ADP

2 ATP

Pyruvate

Pyruvate kinase

Phosphoenolpyruvate

Enolase2

H2O

2-Phosphoglycerate

Phosphoglyceromutase

3-Phosphoglycerate

Phosphoglycerokinase

2 ATP

2 ADP

1, 3-Bisphosphoglycerate

+ 2 H+

6

7

8

9

10

2

2 ADP

2 ATP

Phosphoenolpyruvate

Pyruvate kinase

2 Pyruvate

10

2 P i

Energy investment phase

Glucose

2 ADP + 2

P 2 ATP

used

formed

4 ATP

Energy payoff phase

4 ADP + 4

P

2 NAD+ + 4 e– + 4 H+

2 NADH

+ 2 H+

2 Pyruvate + 2 H2O

2 Pyruvate + 2 H2O

Glucose

Net

4 ATP formed – 2 ATP used

2 ATP

2 NAD+ + 4 e– + 4 H+

2 NADH + 2 H+

Glycolysis Pathway: Summary

29

Glycolysis: Inputs and Outputs

Glycolysisinputs outputs

2 pyruvate

2 NADH

2 ADP

4 ATP total

net gain

glucose

2 NAD+

4 ADP + 4P

ATP

ATP2

2

Pyruvate

is a pivotal metabolite in cellular respiration

If O2 is not available to the cell, fermentation, an anaerobic process, occurs in the cytoplasm. During fermentation, glucose is incompletely

metabolized to lactate, or to CO2 and alcohol (depending on the organism).

If O2 is available to the cell, pyruvate enters mitochondria by aerobic process.

STAGE 2: Transition (Preparatory) Stage Connects glycolysis to the citric acid cycle

End product of glycolysis, pyruvate, enters the mitochondrial matrix

Pyruvate converted to 2-carbon acetyl CoA

Attached to Coenzyme A to form acetyl-CoA

Electron picked up (as hydrogen atom) by NAD+

CO2 released, and transported out of mitochondria into the cytoplasm

CYTOSOL

MITOCHONDRION

NAD+

NADH

+ H+

2

1 3

PyruvateTransport protein

CO2

Coenzyme A

Acetyl CoA

STAGE 3: Citric Acid Cycle/ Krebs Cycle

Pyruvate

NAD+

NADH+ H+ Acetyl

CoA

CO2

CoA

CoA

CoA

Citricacidcycle

FADH2

FAD

CO22

3

3 NAD+

+ 3 H+

ADP +

P

i

ATP

NADH

Occurs in the mitochondria

Fig. 9-12-2

Acetyl CoA

Oxaloacetate

Citrate

CoA—SH

Citric

acidcycl

e

1

2

H2O

Isocitrate

Fig. 9-12-3

Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Citric

acidcycl

e

Isocitrate

1

2

3

NAD+

NADH+ H+

-Keto-glutarate

CO2

Fig. 9-12-4

Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Isocitrate NAD

+NADH+ H+

Citric

acidcycl

e

-Keto-glutarate

CoA—SH

1

2

3

4

NAD+

NADH+ H+Succiny

lCoA

CO2

CO2

Fig. 9-12-5

Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Isocitrate NAD

+NADH+ H+

CO2

Citric

acidcycl

eCoA—SH -Keto-

glutarate

CO2

NAD+

NADH+ H+Succiny

lCoA

1

2

3

4

5

CoA—SH

GTP

GDP

ADP

PiSuccinate

ATP

Fig. 9-12-6

Acetyl CoA

CoA—SH

Oxaloacetate

H2O

Citrate Isocitra

te NAD+

NADH+ H+

CO2

Citric

acidcycl

eCoA—SH -Keto-

glutarate

CO2

NAD+

NADH+ H+

CoA—SH

P

Succinyl

CoA

i

GTP

GDP

ADP

ATP

Succinate

FAD

FADH2

Fumarate

1

2

3

4

5

6

Fig. 9-12-7

Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Isocitrate NAD

+NADH+ H+

CO2

-Keto-glutarate

CoA—SH

NAD+

NADHSucciny

lCoA

CoA—SH

PP

GDP

GTP

ADP

ATP

Succinate

FAD

FADH2

Fumarate

Citric

acidcycl

e

H2O

Malate

1

2

5

6

7

i

CO2

+ H+

3

4

Fig. 9-12-8

Acetyl CoA

CoA—SH

Citrate

H2O

Isocitrate NAD

+NADH+ H+

CO2

-Keto-glutarate

CoA—SH

CO2

NAD+

NADH+ H+

Succinyl

CoA

CoA—SH

Pi

GTP

GDP

ADP

ATP

Succinate

FAD

FADH2

Fumarate

Citric

acidcycl

e

H2O

Malate

Oxaloacetate

NADH+H

+NAD+

1

2

3

4

5

6

7

8

41

Citric Acid Cycle: Balance Sheet

inputs outputs

4 CO26 NADH

2 FADH2

2 acetyl groups6 NAD+

2 FAD

2 ADP + 2 P ATP2

Citric acid cycle

STAGE 4: The Electron Transport Chain Occurs in the cristae of mitrochondrion

Most of the chain’s components are proteins, which exist in multiprotein complexes

The carriers alternate reduced and oxidized states as they accept and donate electrons

Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O

STAGE 4: The Electron Transport Chain

Series of carrier molecules: Pass energy rich electrons successively from one to

another Complex arrays of protein and cytochromes

Cytochromes are respiratory molecules Complex carbon rings with metal atoms in center

Receives electrons from NADH & FADH2

Produce ATP by chemiosis (proton pumps and ATP Synthase)

Oxygen serves as a final electron acceptor Oxygen ion combines with hydrogen ions to form

water

Protein complexof electroncarriers

H+

H+H+

Cyt c

Q

V

FADH2

FAD

NAD+

NADH(carrying

electronsfrom food)

Electron transport chain

2 H+ + 1/2O2

H2

O

ADP +

P i

Chemiosmosis

Oxidative phosphorylation

H+

H+

ATP synthase

ATP

21

Cellular Respiration: Summary

Cellular Respiration Energy Summary: Aerobic In general the flow would be as such for

ATP production: glucose NADH electron transport

chain proton-motive force ATP

About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP HIGH!

Cellular Respiration: Anaerobic and Fermentative

• Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)

In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP

Anaerobic respiration uses an electron transport chain with an electron acceptor other than O2, for example sulfate

Fermentation uses phosphorylation instead of an electron transport chain to generate ATP

Fig. 9-18a

2 ADP + 2

P i 2 ATP

Glucose

Glycolysis

2 Pyruvate

2 NADH

2 NAD+

+ 2 H+

CO2

2 Acetaldehyde

2 Ethanol

(a) Alcohol fermentation

2

Fig. 9-18b

Glucose

2 ADP + 2

P i 2 ATP

Glycolysis

2 NAD+

2 NADH+ 2

H+ 2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

Fermentation and Aerobic Respiration Compared

Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate

The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration

Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

52

Efficiency of Fermentation

Fermentationinputs outputs

2 lactate or2 alcohol and 2 CO2

glucose

2 ADP + 2 P net gainATP2

Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2

Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration

In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

Fermentation and Aerobic Respiration Compared

Fig. 9-19Glucose

Glycolysis

Pyruvate

CYTOSOL

No O2 present:Fermentation

O2 present:

Aerobic cellular respiration

MITOCHONDRIONAcetyl

CoAEthan

olor

lactate Citric

acidcycle

Fermentation: Pros and Cons Advantages

Provides a quick burst of ATP energy for muscular activity.

Disadvantages Lactate is toxic to cells. Lactate changes pH and causes

muscles to fatigue. Oxygen debt and cramping

56

Products of Fermentation

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer

Products of Fermentation

57

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer

Products of Fermentation

58

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer

Review

1. Name the four stages of cellular respiration; for each, state the region of the eukaryotic cell where it occurs and the products that result

2. In general terms, explain the role of the electron transport chain in cellular respiration

4. Explain where and how the respiratory electron transport chain creates a proton gradient for 3 ATP production

5. Distinguish between fermentation and anaerobic respiration

6. Distinguish between obligate and facultative anaerobes

Mitochondria and Alternative Energy Sources

Petite mutants of yeast have defective mitochondria incapable of oxidative phosphorylation. What carbon sources can these mutants use to grow?a. Glucoseb. fatty acidsc. Pyruvated. all of the abovee. none of the above

Glycolysis

To sustain high rates of glycolysis under anaerobic conditions, cells requirea. functioning mitochondria.b. Oxygen.c. oxidative phosphorylation

of ATP.d. NAD+.e. All of the above are correct.

Electron Transport Chain and Respiration 1Rotenone inhibits complex I (NADH dehydrogenase). When complex I is completely inhibited, cells willa. neither consume oxygen

nor make ATP.b. not consume oxygen and

will make ATP through glycolysis and fermentation.

c. not consume oxygen and will make ATP only through substrate-level phosphorylation.

d. consume less oxygen but still make some ATP through both glycolysis and respiration.

Catabolism and Anaerobiosis

During intense exercise, as muscles go into anaerobiosis, the body will increase its consumption ofa. fats.b. proteins.c. carbohydrates.d. all of the above

Evolution of Metabolic PathwaysGlycolysis is found in all domains of life and is therefore believed to be ancient in origin. What can be said about the origin of the citric acid cycle, the electron transport chain, and the F1 ATPase?

a. They evolved after photosynthesis generated free oxygen.

b. They evolved before photosynthesis and used electron acceptors other than oxygen.

c. Individual enzymes were present before photosynthesis but served other functions, such as amino acid metabolism.

d. They evolved when the ancestral eukaryotes acquired mitochondria.