Bio 160- Cellular Respiration and Fermentation

What is cellular respiration?

A set of metabolic reactions that break down glucose using oxygen to make ATP.

Overall cellular respiration equation?

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP).

What is fermentation?

Anaerobic pathway that regenerates NAD⁺ so glycolysis can continue and produce ATP without oxygen.

Relationship between photosynthesis & cellular respiration?

Photosynthesis makes glucose + O₂, respiration breaks them down to ATP + CO₂ + H₂O. They are inverse processes.

Can only glucose enter respiration?

No — fats, proteins, and other carbs can also feed into the pathway at different stages.

Can cellular respiration pathways make precursors?

Yes — used to build amino acids, fats, nucleotides (anabolism).

What are the 4 phases of cellular respiration in order?

1) Glycolysis

• 6-carbon glucose is “split” into 2, 3-carbon pyruvate molecules
  2) Pyruvate Processing

• Pyruvate is oxidized to form acetyl CoA
  3) Citric Acid Cycle

• Acetyl CoA is oxidized to CO2 (the remaining bonds are broken)

• The electrons are removed by redox reactions that pass the electrons to an electron acceptor (NAD+ or FAD+ is reduced)
  4) Electron Transport Chain + Chemiosmosis

• NADH and FADH2 bring the electrons to the electron transport chain and are therefore oxidized when they donate the electrons to the electron transport chain

• The electrons flow down the chain, powering the production of ATP

Where does glycolysis occur & what goes in/out?

Cytosol, Glucose → 2 Pyruvate + 2 ATP + 2 NADH.

Where does pyruvate processing occur & what is produced?

Mitochondrial matrix, Pyruvate → Acetyl-CoA + CO₂ + NADH.

Where does the Citric Acid Cycle occur & what is produced?

Mitochondrial matrix, Acetyl-CoA → CO₂ + NADH + FADH₂ + ATP.

Where does ETC & oxidative phosphorylation occur?

Inner mitochondrial membrane (cristae).

Step that produces most ATP?

Electron Transport Chain + chemiosmosis (oxidative phosphorylation).

How is energy harvested in ETC?

Electrons flow from high → low energy carriers to O₂, releasing energy to pump H⁺.

What is substrate-level phosphorylation?

ATP formed by direct phosphate transfer from substrate → ADP. Occurs in glycolysis + CAC.

What is oxidative phosphorylation?

ATP made using ETC + H⁺ gradient + ATP synthase. Occurs in final stage.

Proton motive force?

H⁺ gradient created across membrane that powers ATP production.

What is chemiosmosis?

Movement of H⁺ through ATP synthase to generate ATP.

How does ATP synthase work?

Acts like a rotary motor; H⁺ flow spins rotor → phosphorylates ADP → ATP.

Why is oxygen required for ETC?

Final electron acceptor; forms H₂O when electrons + H⁺ combine.

What happens if O₂ isn’t available for ETC?

ETC stops → NADH builds up → glycolysis stops unless fermentation occurs.

What inhibits glycolysis & citric acid cycle?

ATP & NADH (feedback inhibition).

Why is fermentation needed without oxygen?

Regenerates NAD⁺, allowing glycolysis to continue & make 2 ATP.

Humans perform what type of fermentation & product?

Lactic acid fermentation → lactate + NAD⁺.

Yeast fermentation product?

Ethanol + CO₂ + NAD⁺.

ATP yield per glucose in aerobic respiration?

~ 29 ATP.

ATP yield per glucose in fermentation?

2 ATP only — very inefficient. (through glycolysis)

Alternative fuel molecules for respiration?

Fats → Glycerol + fatty acids
Proteins → amino acids enter CAC.

Other uses of metabolism besides energy?

Biosynthesis of nucleotides, lipids, proteins, glycogen. Precursors come from glycolysis & CAC.