7.2.4 - Link Reaction & Krebs Cycle

Question 1

Describe Pyruvate
(2 Points)

Answer 1

~ Is the end product of glycolysis.

~ It contains loads of chemical energy, which can be used to produce more ATP.

Question 2

How Does Pyruvate Enter The Mitochondria?
(3 Points)

Answer 2

~ Once oxygen is available, pyruvate will enter the matrix.

~ Moves across the double membrane via active transport, requiring a transport protein and a small amount of ATP.

~ Once inside the matrix, it takes part in the link reaction.

Question 3

Describe The Link Reaction
(2 Points)

Answer 3

~ Takes place in the matrix of the mitochondria.

~ Links glycolysis and the Krebs cycle.

Question 4

Why Do The Link Reaction & Krebs Cycle Occur Twice?
(3 Points)

Answer 4

~ For every molecule of glucose that enters glycolysis, 2 pyruvate molecules are produced.

~ 2 acetyl CoA molecules are produced from each glucose molecule, so 2 cycles are required per glucose molecule.

~ Therefore the link reaction and the Krebs cycle, occur twice for every glucose molecule.

Question 5

What Does The Link Reaction & The Krebs Cycle Produce, For One Glucose Molecule?
(3 Points)

Answer 5

~ Acetyl CoA.

~ CO2.

~ Reduced NAD.

Question 6

What Does The Link Reaction & The Krebs Cycle Produce, For Two Glucose Molecules?
(3 Points)

Answer 6

~ 2 acetyl CoA molecules.

~ 2 CO2 molecules.

~ 2 reduced NAD molecules.

Question 7

Describe The Process Of The ‘Link Reaction’
(5 Points)

Answer 7

~ Pyruvate is oxidised (Loss of hydrogen), by enzymes to produce acetate.

~ Pyruvate is also decarboxylated (Carbon is removed), in the form of CO2.

~ NAD is reduced, as it collects hydrogen from pyruvate, changing pyruvate into acetate.

~ Acetate combines with CoA, to form acetyl CoA.

~ No ATP is produced.

Question 8

What Is The Krebs Cycle?
(2 Points)

Answer 8

~ Series of oxidation and reduction reactions.

~ With each of these reactions, being controlled by a specific intracellular enzyme.

Question 9

Describe The Process Of The ‘Krebs Cycle’
(7 Points)

Answer 9

~ Acetyl CoA (2C), from the link reaction, combines with oxaloacetate (4C), to form citrate (6C).

~ CoA is then released, to be reused in the link reaction.

~ Decarboxylation (Carbon is removed) of citrate (6C), removing CO2.

~ Dehydrogenation (Hydrogen is removed), to produce reduced NAD, from NAD.

~ Citrate (6C), is then converted into a intermediate (5C).

~ Decarboxylation and dehydrogenation occur, producing reduced FAD and 2 molecules of reduced NAD.

~ Substrate linked phosphorylation occurs, producing 1 molecule of ATP.

Question 10

What Is ‘Substrate Linked Phosphorylation’ Of The Krebs Cycle?

Answer 10

A phosphate is transferred from one of the intermediates to ADP, forming 1 ATP to supply energy.

Question 11

What Are The Products Of The Krebs Cycle, At The End Of 2 Cycles?
(4 Points)

Answer 11

~ 2 ATP.

~ 6 reduced NAD.

~ 2 reduced FAD .

~ 4 CO2.