Respiration

Question 1

Why is respiration important?

Answer 1

● Respiration produces ATP (to release energy)
● For active transport, protein synthesis

Question 2

Summarise the stages of aerobic respiration

Answer 2

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

Question 3

Summarise stages of anerobic respiration

Answer 3

1. Glycolysis - cytoplasm
2. NAD regeneration - cytoplasm

Question 4

Describe the process of glycolysis

Answer 4

1. Glucose phosphorylated to glucose phosphate
   ○ Using inorganic phosphates from 2 ATP
2. Hydrolysed to 2 x triose phosphate
3. Oxidised to 2 pyruvate
   ○ 2 NAD reduced
   ○ 4 ATP regenerated

Question 5

Explain what happens after glycolysis if respiration is anaerobic

Answer 5

1. Pyruvate converted to lactate (animals & some bacteria) or ethanol (plants & yeast)
2. Oxidising reduced NAD → NAD regenerated
3. So glycolysis can continue (which needs NAD) allowing continued production of ATP

Question 6

Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration

Answer 6

● Only glycolysis involved which produces little ATP (2 molecules)
● No oxidative phosphorylation which forms majority of ATP

Question 7

What happens after glycolysis if respiration is aerobic?

Answer 7

Pyruvate is actively transported into the mitochondrial matrix

Question 8

Describe the link reaction

Answer 8

1. Pyruvate oxidised and decarboxylated to acetate
   ○ CO2 produced
   ○ Reduced NAD produced (picks up H)
2. Acetate combines with coenzyme A, forming Acetyl Coenzyme A

Question 9

Describe the Krebs cycle

Answer 9

1. Acetyl coenzyme A (2C) reacts with a 4C molecule
   ○ Releasing coenzyme A
   ○ Producing a 6C molecule that enters the Krebs cycle
2. In a series of oxidation-reduction reactions, the 4C molecule is regenerated and:
   ○ 2xCO2lost
   ○ Coenzymes NAD & FAD reduced
   ○ Substrate level phosphorylation
   (direct transfer of Pi from intermediate compound to ADP) → ATP produced

Question 10

Describe the process of oxidative phosphorylation

Answer 10

1. Reduced NAD/FAD oxidised to release H atoms → split into protons (H+) and electrons (e-)
2. Electrons transferred down electron transfer chain
   ○ By redox reactions
3. Energy released by electrons used in the production of ATP from ADP + Pi (chemiosmotic theory):
   ○ Energy used by electron carriers to actively pump protons from matrix into intermembrane space
   ○ Protons diffuse into matrix down an electrochemical gradient, via ATP synthase (embedded)
   ○ Releasing energy to synthesise ATP from ADP + Pi
4. In matrix at end of ETC, oxygen is final electron acceptor (electrons can’t pass along otherwise)
   ○ So protons, electrons and oxygen combine to form water

Question 11

Give examples of other respiratory substrates

Answer 11

● Fatty acids from hydrolysis of lipids → converted to Acetyl Coenzyme A
● Amino acids from hydrolysis of proteins → converted to intermediates in Krebs cycle

Question 12

Products of glucose in kreb cycle

Answer 12

6 x reduced NAD, 2 x reduced FAD, 2 x ATP and 4 x CO2