5.2 Respiration

Question 1

Why is respiration important?

Answer 1

● Respiration produces ATP (to release energy)

● For active transport, protein synthesis etc.

Question 2

Summarise the stages of aerobic respiration

Answer 2

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

Question 3

Summarise the stages of anaerobic 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 (net gain of 2)

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 (around 34 molecules)

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:
   ○ 2 x CO2 lost
   ○ 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 (chain of carriers at decreasing energy levels)
   ○ 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 → 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

Breakdown products of lipids and amino acids, which enter the Krebs cycle. For example:

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