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Chapter 9. Biology Sixth Edition Raven/Johnson (c) The McGraw-Hill Companies, Inc. Drives ATP synthesis. Cellular respiration is the step-wise release of energy from molecules (usually carbohydrates) used to synthesize ATP molecules.

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Chapter 9

Chapter 9

Biology

Sixth Edition

Raven/Johnson

(c) The McGraw-Hill Companies, Inc.


Drives ATP synthesis

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

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.


The NAD+ cycle

Remember:

When NAD+ NADH it has been reduced.

Remember:

When NADHNAD+ it has been oxidized.


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


Outside the Mitochondria: Glycolysis

Universally found in all organisms.

Does not require oxygen.


Overview of Glycolysis

Glucose (6-C sugar)

2 ATP

2 ADP

6-C sugar diphosphate

3-C sugar-phosphate

3-C sugar-phosphate

2 ADP

2 ADP

2 ATP

2 ATP

2 NAD+

2 NAD+

2 NADH

2 NADH

3-C pyruvate

3-C pyruvate


Glycolysis summary

Inputs:

Glucose

2 NAD+

2 ATP

4 ADP + 4 P

Outputs:

2 pyruvate

2 NADH

2 ADP

4 ATP (2 net gain)


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)

Pyruvate

(Oxygen present)

(Oxygen not present)

Cellular Respiration

Fermentation


2-carbon molecule + 1 CO2

3-carbon molecule + 0 CO2


2 NAD+

2 NADH + H+

2Pyruvate + 2CoA

2 Acetyl-CoA + 2CO2

Pyruvate oxidation: if oxygen is present

Pyruvate is converted to a C2acetyl group attached to coenzyme A (CoA), and CO2is 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 C6citrate results.


Acetyl-CoA (2 C)

NAD+

C6

NADH

C4

CO2

NADH

NAD+

C5

Krebs cycle

FADH2

NAD+

FADH

NADH

C4

CO2

ATP

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 electron transport system then combines with hydrogen to form water: + O2 CO2 + H2O + ATP


Glycolysis electron transport system then combines with hydrogen to form water:

Transition

Reaction

Krebs

Cycle

NAD+

Electron

Transport

Chain

NADH

Remember: Electrons = Energy


Feedback mechanisms electron transport system then combines with hydrogen to form water:


Acidic group electron transport system then combines with hydrogen to form water:

H group

Amino group

R-group


With electron transport system then combines with hydrogen to form water: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

The End. transfer of a phosphate group from PEP to ADP to create ATP. The energy in the bond is conserved.


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