5.2 Respiration

Question 1

Aerobic respiration consists of 4 stages, What are they?

Answer 1

Glycolysis
The link Reaction
Krebs cycle
Oxidative phosphorylation

Question 2

Glycolysis:

Answer 2

Glycolysis is the first stage of anaerobic and aerobic respiration.
Glycolysis occurs in the cytoplasm and is an anaerobic process.

Glycolysis involves the following stages:
Phosphorylation of glucose to glucose phosphate, using ATP.
Production of triose phosphate.
Oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD.

Question 3

The link reaction:

Answer 3

Link reaction occurs in the matrix.
Pyruvate is oxidised to acetate, producing reduced NAD (and waste CO₂) in the process.
Acetate combines with coenzyme A to produce acetylcoenzyme A.

Question 4

The Krebs cycle:

Answer 4

The Krebs cycle occurs in the matrix.
Acetylcoenzyme A reacts with a four-carbon molecule, releasing coenzyme A and producing a six-carbon molecule that enters the Krebs cycle.
in a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes (NAD and FAD) and ATP by substrate-level phosphorylation, and CO₂ is lost

Question 5

Oxidative phosphorylation:

Answer 5

Oxidative phosphorylation occurs on the cristae.
Synthesis of ATP by oxidative phosphorylation is associated with the transfer of electrons down the electron transfer chain and passage of protons across inner mitochondrial membranes, and is catalysed by ATP synthase embedded in these membranes (chemiosomotic theory).

Reduced NAD and FAD pass electrons to the electron transfer chain. Energy from these electrons is used by the electron transfer chain to pump protons into inter-membranal space, generating an electrochemical proton gradient which allows ATP synthase to use the proton motive force to produce ATP.

Oxygen is the final electron acceptor.

Question 6

Apart from carbohydrates, what else can be respired?

Answer 6

Other respiratory substrates include the breakdown products of lipids and amino acids, which enter the Krebs cycle.

Question 7

Anaerobic respiration:

Answer 7

If respiration is only anaerobic, pyruvate can be converted to ethanol or lactate using reduced NAD. The oxidised NAD produced in this way can be used in further glycolysis.

Question 8

Compare and contrast anaerobic respiration of glucose in yeast and muscle cells.

Answer 8

Similarities:
ATP used
ATP formed
pyruvate formed
pyruvate reduced
NAD is reduced and oxidised

Differences:
Ethanol formed by yeast, lactate formed by muscle cell
Ethanal is hydrogen acceptor in yeast, pyruvate is hydrogen acceptor in muscle cell
CO₂ released by yeast but not by muscle cell;