3 - Respiration

Question 1

4 stages of aerobic respiration

Answer 1

Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation

Question 2

Glycolysis

Answer 2

Occurs in cytoplasm

1) phosphorylation of glucose (6C) to glucose phosphate
-requires 2 ATP

2) splitting of glucose phosphate to produce two molecules of triose phosphate (3C)

3) oxidation of triose phosphate to pyruvate (3C)
-electrons and hydrogen reduce NAD to NADH+
-phosphate groups turn ADP to ATP via substrate-level phosphorylation
1 NADH per triose phosphate
2 ATP per triose phosphate

Products of Glycolysis:
-2 x pyruvate (3C)
- 2 x ATP
- 2 x reduced NAD

Question 3

The Link Reaction

Answer 3

Pyruvate and NADH+ actively transported into mitochondrial matrix

Pyruvate oxidised to acetate, producing NADH and CO2

Acetate combines with coenzyme A to form acetylcoenzymeA

Products of Link Reaction per molecule of glucose:
- 2 x Acetyl CoA
- 2 x CO2
- 2 x reduced NAD

Question 4

The Krebs Cycle

Answer 4

Acetyl CoA releases 2C molecule that reacts with oxaloacetate(4C) to form citrate (6C)

coenzyme A freed up and returned back to link reaction

series of redox reaction occurs:
- citrate(6C) turns back into oxaloacetate(4C)
-ATP produced by substrate-level phosphorylation
-carbon dioxide is lost
-reduced coenzymes NAD and FAD produced

Products of Krebs Cycle per molecule of glucose:
- 6 x reduced NAD
- 2 x reduced FAD
- 2 x ATP
- 4 x CO2

Question 5

Oxidative Phosphorylisation

Answer 5

Takes place on cristae of inner mitochondrial membrane

Hydrogen atoms from reduced NAD and FAD split into protons and electrons

electrons enter electron transport chain and energy is released as they pass through electron carriers

energy released used to actively transport protons across inner mitochondrial membrane from matrix to intermembrane space

protons move down their concentration gradient back to matrix by facilitated diffusion; they move via proton channels that are associated with ATP synthase

ATP synthase catalyses the formation of ATP from ADP and P

At end of chain, electrons pass to oxygen, which is the final electron acceptor

Water formed as waste product

Question 6

anaerobic respiration

Answer 6

Ethanol and lactate fermentation allow NAD to be regenerated so that glycolysis can continue

Ethanol fermentation
-pyruvate decarboxylated to ethanal
-ethanal is reduced to ethanol
-NADH oxidised to NAD

Lactate fermentation
-Pyruvate accepts hydrogen from NADH and is reduced to lactate
-NADH oxidised to NAD