Lecture 14: Cellular Respiration: Oxidative Phosphorylation and Fermentation

Oxidative Phosphorylation

produces the most ATP

- chemiosmosis and electron transport chain

Electron Transport Chain

NADH and FADH2: energy extracted from glucose

- donate electrons to electron transport chain which powers ATP synthesis through oxidative phosphorylation

- forms a proton gradient across inner membrane (H+)

Chemiosmosis

movement of H+ gradient across a membrane to drive cellular work

Proton Motive Force

the force that promotes movement of protons across membranes

- H+ gradient

Energy Flow During Cellular Respiration

glucose > NADH > electron transport chain > proton motive force > ATP

- makes about 32 ATP; remaining energy from glucose is lost as heat

Steps of Cellular Respiration

- glycolysis (phase I and II; generates 4 ATP)

- pyruvate oxidation

- citric acid cycle

- oxidative phosphorylation (electron transport chain; chemiosmosis)

Cellular Respiration Waste Products

H20 and O2

Anaerobic Respiration and Fermentation

absence of O2

- both processes begin with glycolysis

Fermentation: sulfur

Anaerobic Resp.: electron transport chain

Fermentation

regenerate NAP+ so cells can gain some ATP

- regenerated by electron transfer of NADH to pyruvate

- alcohol fermentation and lactic acid fermentation

Glycolysis in the Absence of O2

pyruvate can be fermented into ethanol or lactate

- regenerates NAD+ to feed back into glycolysis

- in presence, pyruvate is further oxidized to CO2

Lactic Acid Fermentation

pyruvate is directly converted to lactate without producing CO2

- human muscle cells; low oxygen conditions

Alcohol Fermentation

pyruvate is converted into ethanol in two steps:

- convert pyruvate to acetaldehyde by releasing CO2

- acetaldehyde is reduced by NADH to ethanol

- yeast cells; low oxygen conditions

Obligate Anaerobes

use only fermentation or anaerobic respiration

- cannot survive in presence of O2

Facultative Anaerobes

use both cellular respiration in presence of O2 or fermentation

- can switch back and forth with no problem

- yeast and bacteria

Evolutionary Significance of Glycolysis

- early prokaryotes relied entirely on glycolysis

- occurs in cytosol, indicating that it likely evolved before mitochondria