5.2 respiration

Question 1

Glycolysis

Answer 1

In cytoplasm

1. Phosphorylation of glucose to glucose phosphate
   - using the inorganic phosphates from 2 ATP
2. Hydrolysed to 2x triose phosphate
3. 2x triose phosphate oxidised to 2x pyruvate
   - 2 NAD reduced
   - 4 ATP regenerated

4 ATP gained, 2 used = net production of ATP

Question 2

Anaerobic respiration (if O2 not present)

Answer 2

1. Pyruvate converted to lactate or ethanol
2. Oxidising reduced NAD > NAD regenerated
3. So glycolysis can continue which needs / uses NAD

Question 3

Aerobic respiration (if O2 present)

Answer 3

Pyruvate actively transported into mitochondrial matrix

Stages: glycolysis, link reaction, kerbs, oxidative phosphorylation

Question 4

Link reaction

Answer 4

In mitochondrial matrix

Pyruvate oxidised and decarboxylated = acetate
- CO2 and reduced NAD produced

Acetate combines with coenzyme A = acetyl coenzyme A

Per glucose molecule, 2x acetyl CoA, 2x CO2 and 2x reduced NAD produced

Question 5

krebs cycle

Answer 5

In mitochondrial matrix

Acetyl CoA reacts with 4C molecule (oxaloacetate), producing a 6C molecule (citrate) that enters the Krebs cycle
- Coenzyme A released

6C molecule > 5C > 4C molecule (4C regenerated) through a series of oxidation-reduction reactions ….

Decarboxylation and dehydrogenation
- CO2 removed
- coenzymes NAD and FAD reduced

ATP produced by substrate level phosphorylation from ADP and Pi

Question 6

Oxidative phosphorylation

Answer 6

On cristae of mitochondria

Reduced NAD/FAD oxidised to release H atoms > split into protons (H+) and electrons (e-)

Electrons transferred down the electron transport chain (chain of carriers at decreasing energy levels by redox reactions)

Energy released by electrons used in production of ATP from ADP + Pi (chemiosmotic theory)
- energy used by electron carriers to actively transport protons from matrix to inter membrane space
- protons diffuse down electrochemical gradient, via ATP synthase back into matrix
- releasing energy to combine ADP + Pi to ATP

In matrix at the end of the electron transport chain, oxygen is final electron acceptor - protons, electrons and oxygen combine to form water

Question 7

Why is oxygen needed for production of ATP on cristae of mitochondrion

Answer 7

Oxygen = terminal electron acceptor for electrons passing along the ETC

ETC releases energy for formation of most ATP from ADP and PI

No oxygen to accept them = electrons cant be passed along electron transport chain

Krebs cycle and link reaction also stop in absence of oxygen because NAD and FAD cannot be produced

Question 8

Other respiratory substances

Answer 8

Include the breakdown of lipids and amino acids, which enter Krebs cycle

Fatty acids from hydrolysis of lipids converted to acetyl coenzyme A

Amino acids from hydrolysis of proteins converted to intermediates in krebs