Respiration

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Four stages:

1. Glycolysis (cytoplasm)
2. Link reaction (mitochondrial matrix)
3. Krebs cycle (mitochondrial matrix)
4. Oxidative phosphorylation (inner mitochondrial membrane)

Occurs in cytoplasm. Anaerobic (no O₂ needed).

1. Glucose (6C) → phosphorylated by 2 ATP
2. Split into 2 × triose phosphate (3C)
3. Oxidised → 2 × pyruvate (3C)
4. Net gain: 2 ATP + 2 reduced NAD

Pyruvate enters mitochondrial matrix.

$\text{Pyruvate (3C)} \rightarrow \text{Acetyl CoA (2C)} + \text{CO}_2 + \text{reduced NAD}$

Happens twice per glucose.

In mitochondrial matrix. Per turn:

1. Acetyl CoA (2C) + oxaloacetate (4C) → citrate (6C)
2. Citrate decarboxylated and dehydrogenated through series of steps
3. Oxaloacetate regenerated

Per turn: 1 ATP, 3 reduced NAD, 1 reduced FAD, 2 CO₂ Per glucose (×2): 2 ATP, 6 reduced NAD, 2 reduced FAD, 4 CO₂

On inner mitochondrial membrane (cristae).

1. Reduced NAD and reduced FAD donate electrons to electron transport chain
2. Electrons pass along carriers → energy released
3. Energy pumps H⁺ from matrix into intermembrane space
4. H⁺ flows back through ATP synthase → chemiosmosis → ATP produced
5. O₂ is final electron acceptor → combines with H⁺ and electrons → H₂O

Produces approximately ~26-28 ATP per glucose (from reduced NAD and FAD).

In animals: pyruvate + reduced NAD → lactate + NAD In yeast: pyruvate → ethanal + CO₂; ethanal + reduced NAD → ethanol + NAD

Purpose: regenerate NAD so glycolysis can continue.

• Glycolysis: glucose → 2 pyruvate + 2 ATP + 2 reduced NAD (cytoplasm)
• Link: pyruvate → acetyl CoA + CO₂ + reduced NAD
• Krebs: acetyl CoA → CO₂ + ATP + reduced NAD/FAD
• Oxidative phosphorylation: ETC + chemiosmosis → most ATP; O₂ final electron acceptor
• Total: ~30-32 ATP per glucose