Link Reaction And Krebs Cycle 12.3

Question 1

An investigation was carried out into the production of ATP by mitochondria. ADP, phosphate, excess substrate and oxygen were added to a suspension of isolated mitochondria.
I) suggest substrate used for this investigation (1)

II) explain why the concentration of oxygen and amount of ADP fell during the investigation (2)

Answer 1

I) pyruvate /succinate /any suitable Krebs cycle substrate

II)
1. ADP and phosphate forms ATP/ Oxygen used to form water / as terminal acceptor

Question 2

Describe how acetylcoenzyme A is formed in the link reaction

2

Answer 2

1. Oxidation of / hydrogen removed from pyruvate and carbon dioxide released
2. Addition of coenzyme A

Question 3

Explain how oxaloacetate enables the acetylcoenzyme A to then bind to enzyme citrate synthase?
(2)

Answer 3

1. Change in site of active site / active site moulds around the substrate
2. Substrate/ active site now complementary

Question 4

Suggest how production of of succinyl coenzyme A could control the rate of the reaction catalysed by citrate synthase?
(2)

Answer 4

1. Is a competitive inhibitor / attaches to active site

2. Reduces/ prevents enzyme substrate complex forming

Question 5

In muscles pyruvate is converted to lactate during anaerobic respiration
I) explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration
(2)

Answer 5

1. Regenerates / produces NAD / oxidises reduced NAD

2. NAD used in glycolysis

Question 6

In muscles pyruvate is converted to lactate during anaerobic respiration
II) in muscles some of the lactate is converted back to pyruvate when they are well supplied with oxygen suggest one advantage of this:
(1)

Answer 6

1. Pyruvate used in aerobic respiration / lactic acid is toxic / harmful / causes cramp

Question 7

What is a transcription factor ?

3

Answer 7

1. Protein / molecule that moves from cytoplasm to DNA
2. TF binds to specific gene / binds to promotor / site on DNA
3. Leads to pre mRNA production / allows binding of RNA polymerase / allows RNA polymerase to work