Bio 107 Ch. 7: Cellular Respiration

Cellular Respiration

breakdown of glucose and other molecules to produce ATP

How ATP much does 1 glucose produce?

36-38 ATP

Aerobic vs Anaerobic

Aerobic: requires oxygen, produces 36-38 ATP, and produces CO2

Anaerobic: oxygen NOT required, produces 2 ATP, and produces lactic acid or ethanol

NAD+ and FAD

coenzymes and electron and hydrogen carriers that pick up electrons at specific enzymatic reactions and deliver to the electron transport chain

• NAD+ (oxidized) to NADH (reduced)

• FAD (oxidized) to FADH2 (reduced)

Stages of Cellular Respiration

Glycolysis

Pyruvate Oxidation/Prep Reaction

Citric Acid Cycle

Electron Transport Chain and Chemiosmosis

Pyruvate

end-product of glycolysis and converted into Acetyl-CoA, which fuels citric acid cycle

Glycolysis

breakdown of glucose into 2 pyruvate molecules, occurs in cytoplasm, and does NOT require oxygen (anaerobic)

• Glucose + 2 ATP + 2 NAD+ = 2 Pyruvate + 4 ATP + 2 NADH

• uses oxidation

Oxidation

removal of electrons and hydrogen ions provides energy for immediate ATP buildup

Pyruvate Oxidation (Preparatory Reaction)

pyruvate is oxidized into Acetyl CoA, carbon dioxide is removed, located in mitochondrial matrix, and requires oxygen (aerobic)

• occurs twice because glycolysis produces 2 pyruvate

• Pyruvate + Released CO2 + NAD+ = Acetyl CoA + 2 NADH + CO2

Citric Acid Cycle

cyclical series of oxidation reactions produces 1 ATP and 1 CO2 per turn

• Acetyl CoA fuels this

• 1 glucose (stored in NADH) = 2 turns (2 Acetyl CoA) = 4 CO2 + 6 NADH + 2 FADH2 + 2 ATP

Electron Transport Chain

series of electron carrier molecules, located in cristae, that produces ATP under aerobic conditions

1. NADH and FADH2 donate electrons

2. electrons pass through proteins in the membrane

3. energy from electrons pump H+ ions into inter-membrane space

4. oxygen is the final electron acceptor, forming H2O

5. H+ flows back through ATP synthesis, powering ATP production

6. 32-34 ATP produced

Electron Transport Chain Cont.

• high-energy molecules enter and low-energy molecules leave

• energy is captured as electrons pass between carriers and stored as a H+ ion concentration gradient to form water

Which acceptors do NADH and FADH2 pass to?

NADH passes to 1st acceptor and FADH2 passes to 2nd acceptor

Proton Gradient

protons accumulate in the inter-membrane space more than in the matrix

ATP Synthase Complexes

the cristae contains these in which H+ ions flows THROUGH then BACK into matrix

Chemiosmosis

high to low movement of H+ ions which drives ATP production from ADP

Anaerobic Pathways (Outside Mitochondria): Glycolysis

when oxygen us unavailable, fermentation occurs to regenerate NAD+ for glycolysis

Energy Investment Steps

2 ATP used to activate glucose as glycolysis begins

Energy Harvesting Steps

oxidation of G3P to generate NADH and ATP

• Substrate-Level Phosphorylation occurs

Substrate-Level Phosphorylation

direct formation of 4 ATP due to additional chemical changes

Fermentation

if oxygen is limited, cells may utilize anaerobic pathways

• 2 forms: Lactic Acid Fermentation and Alcohol Fermentation

Lactic Acid Fermentation

in animal cells, pyruvate is reduced (gains electrons) to lactate and enables glycolysis to continue

• NAD+ is regenerated for use in glycolysis

Lactate

toxic to cells and changes the pH of muscles which causes the “burning” sensation when active

Alcohol Fermentation

in yeasts, pyruvate is reduced to ethyl alcohol, enables glycolysis to continue with NAD+ regeneration, and releases CO2

• provides rapid burst of ATP

• ex. when muscles work vigorously over short period of time

Energy Yield of Fermentation

fermentation yield only 2 ATP from substrate-level phosphorylation which represents a small fraction of the potential energy stored in glucose, therefore, it is NOT released