aerobic respiration

number of ATP molecules produced during only aerobic respiration: 30

1. glycolysis → 7 ATP

2.5 ATP is made from each reduced NAD

(2 NADH = 2.5 × 2 = 5)

(net gain of 2 ATP)

2. link reaction (2) → 5 ATP

(2 NADH = 2.5 × 2 = 5)

3. krebs cycle (2) → 20 ATP

(6 NADH = 2.5 × 6 = 15)

1.5 ATP is made from each reduced FAD

(2 FADH = 1.5 × 2 = 3)

Describe the process of glycolysis

1. activation of glucose through phosphorylation:

• 2 ATP is hydrolysed into 2x ADP + Pi

• molecule combining glucose and 2Pi is formed (phosphorylated glucose) - glucose phosphate

2. splitting / hydrolysis of phosphorylated hexose sugar:

• adding Pi lowers the activation energy, so molecule is unstable

• splits into 2x triose phosphate

3. oxidation of triosephosphate:

• each TP loses 2H

• 2NAD + 4H →2NADH

4. substrate level phosphorylation:

• TP may have picked up more Pi from cytoplasm

• these Pi are recycled to produce more ATP

• 2x ADP + Pi →2x ATP

5. resulting in 2x pyruvate:

• 3C molecule

• small enough to diffuse/actively transport into mitochondria

why is glycolysis in cytoplasm?

6C molecule is too large to enter mitochondria, needs to split into 2x pyruvate first so it can diffuse across the double membrane of mitochondria

molecules produced in glycolysis

ATP: net gain 2 (2 used in first step - 4 produced in total)

NADH: 2

Describe what happens during glycolysis. (5 marks)

• Glucose is phosphorylated using 2 ATP molecules.

• This produces two molecules of triose phosphate.

• Each triose phosphate is oxidised to form pyruvate.

• 2 NAD are reduced to form 2 NADH

• 4 ATP are produced via substrate-level phosphorylation, with a net gain of 2 ATP

describe link reaction (matrix)

1. pyruvate is oxidised (NAD + 2H → NADH)

2. pyruvate is decarboxylated (loses a CO2)

3. this produces acetate (2C compound)

4. coenzyme A combines with acetate

5. resulting in acetyl coA (still 2C compound)

ATP Yield (Theoretical)

• glycolysis : net gain 2

• krebs : 2

• oxidative phosphorylation : 28

• total : 32

describe oxidative phosphorylation: cristae

1. coenzymes are oxidised (lose electrons and hydrogen)

2. electrons are transferred down ETC, releasing energy

3. this energy is used to pump protons into intermembrane space: creates electrochemical / proton gradient

4. protons move back down gradient into matrix through channel in ATP synthase

5. (chemiosmosis): allows for phosphorylation of ADP + Pi → ATP

6. oxygen final electron acceptor:

• picks up electrons after they leave the final electron carrier protein at end of ETC

• picks up protons from matrix

• combined with each to form water

7. 4 electrons + 4 protons → 2 water

without oxygen:

• electrons cannot pass down ETC because they have nowhere to go after

• electron carriers in ETC remain full

• coenzymes can’t be oxidised

• NAD and FAD aren’t regenerated

• no chemiosmosis

• less ATP

how does no oxygen affect link and krebs reaction?

• link stops: NAD not regenerated, pyruvate can’t be oxidised to acetyl CoA

• krebs stops: NAD/FAD not regenerated, so these coenzymes can’t be reduced again.

why does NADH produce more ATP than FADH

• NADH donates electrons at higher energy level

• electrons pass through more carriers

• MORE protons are pumped into intermembrane space

• so larger proton gradient = more ATP