Cellular Respiration Harvesting Chemical Energy

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Glucose

2 ADP + 2

P

i

2 ATP

Glycolysis

2 NAD+

2 NADH

+ 2 H+

2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

Slide 73

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

Slide 74

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

Slide 75

Fig. 9-19

Glucose

Glycolysis

Pyruvate

CYTOSOL

No O2 present:

Fermentation

O2 present:

Aerobic cellular

respiration

MITOCHONDRION

Acetyl CoA

Ethanol

or

lactate

Citric

acid

cycle

Slide 76

The Evolutionary Significance of Glycolysis

Glycolysis occurs in nearly all organisms

Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

Slide 77

Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways

Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways

Slide 78

The Versatility of Catabolism

Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration

Glycolysis accepts a wide range of carbohydrates

Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle

Slide 79

Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA)

Fatty acids are broken down by beta oxidation and yield acetyl CoA

An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate

Slide 80

Fig. 9-20