Chapter 9

BiologySixth Edition

Raven/Johnson

(c) The McGraw-Hill Companies, Inc.

Cellular respiration is the step-wise release of energy from molecules (usually carbohydrates) used to synthesize ATP molecules.

Drives ATP synthesis

Oxidation of glucose is an exergonic reaction (releases energy) which drives ATP synthesis - an endergonic reaction (energy is required).

Overall reaction for cellular respiration:

NAD+ and FAD• Each step of cellular respiration requires a

separate enzyme• Some enzymes use the oxidation-reduction

coenzyme NAD+ or the coenzyme FAD.

Remember:When NAD+ NADH it has been reduced.

Remember:When NADH NAD+ it has been oxidized.

The NAD+ cycle

4 Phases of Complete Glucose Breakdown

• Glycolysis - yields 2 ATP• Pyruvate oxidation – oxidation reaction• Krebs cycle – yields 2 ATP• Electron transport chain – yields 32-34 ATP

• Net ATP produced from respiration: 36-38

Universally found in all organisms.

Does not require oxygen.

Outside the Mitochondria: Glycolysis

Glucose (6-C sugar)

3-C sugar-phosphate 3-C sugar-phosphate

3-C pyruvate 3-C pyruvate

Overview of Glycolysis

6-C sugar diphosphate2 ADP

2 ATP

2 NADH

2 ATP

2 NADH

2 ATP

2 ADP 2 ADP

2 NAD+ 2 NAD+

Glycolysis summary

Inputs:

Glucose

2 NAD+

2 ATP

4 ADP + 4 P

Outputs:

2 pyruvate

2 NADH

2 ADP

4 ATP (2 net gain)

Pyruvate

(Oxygen present) (Oxygen not present)

Cellular Respiration Fermentation

Fermentation inputs and outputs per glucose molecule

Inputs:

glucose

2 ATP

4 ADP + 4 P

Outputs:

2 lactate or 2 alcohol and 2 CO2

2 ADP

4 ATP (2 net gain)

2-carbon molecule + 1

CO2

3-carbon molecule + 0

CO2

2Pyruvate + 2CoA 2 Acetyl-CoA + 2CO2

2 NAD+ 2 NADH + H+

Pyruvate oxidation: if oxygen is present

Pyruvate is converted to a C2 acetyl group attached to coenzyme A (CoA), and CO2 is released. This occurs in the cytoplasm if oxygen is present.

Krebs Cycle• The Krebs cycle is a cyclical metabolic

pathway located in the matrix of the mitochondria.

• At the start of the citric acid cycle, CoA carries the C2 acetyl group to join a C4 molecule, and C6 citrate results.

C4

Acetyl-CoA (2 C)

C6NADH

CO2

C5

NADH

CO2

ATP

C4

FADH2

NADH

Krebs cycleNAD+

NAD+

NAD+

FADH

ADP + P

Krebs 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

Electron Transport Chain• The electron transport chain located in the

cristae of mitochondria is a series of protein carriers

• Electrons carried by NADH and FADH2 enter the electron transport chain.

• As a pair of electrons is passed from carrier to carrier, energy is released and is used to form ATP molecules by oxidative phosphorylation.

Oxygen receives energy-spent electrons at the end of the electron transport system then combines with hydrogen to form water:

½ O2 + 2 e- + 2 H+ → H2O

Glucose + O2 CO2 + H2O + ATP

NAD+

NADH

Glycolysis

Transition

Reaction

Krebs

Cycle

Electron

Transport

Chain

Remember: Electrons = Energy

Feedback mechanisms

R-g

rou

p

Acidic group

Amino group

H group

With Beta-oxidation the last two carbons of a fatty acid chain enter the Krebs cycle.

This process is repetitive until the entire fatty acid chain is consumed.

A 6 Carbon fatty acid molecule produces more ATP than a glucose (based on the amount of NADH and FADH2 produced.

When PEP transfers a phosphate group to ADP, pyruvate is formed. This is called substrate level phosphorylation.

ADP and PEP are substrates and an enzyme facilitates the transfer of a phosphate group from PEP to ADP to create ATP. The energy in the bond is conserved.

The End.