7.2.4 - Link Reaction & Krebs Cycle

Question 1

Describe Pyruvate
(2 Points)

Answer 1

~ End product of glycolysis.

~ It contains a substantial amount of chemical energy, which can be further utilised in respiration to produce more ATP.

Question 2

Describe The Mitochondrial Matrix

Answer 2

Enzymes and coenzymes required for the link reaction are found here.

Question 3

How Does Pyruvate Enter The Mitochondria?
(3 Points)

Answer 3

~ Once oxygen is available pyruvate will enter.

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

~ Once inside it takes part in the link reaction.

Question 4

Describe The Link Reaction
(2 Points)

Answer 4

~ Takes place in the matrix of the mitochondria.

~ Links glycolysis and the Krebs cycle.

Question 5

What Does The Link Reaction Produce?
(3 Points)

Answer 5

~ Acetyl CoA.

~ CO2.

~ Reduced NAD.

Question 6

Describe The Steps Of The Link Reaction
(5 Points)

Answer 6

~ Pyruvate is oxidised by enzymes to produce acetate.

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

~ NAD is reduced, as it collects hydrogen from pyruvate, pyruvate -> acetate.

~ Acetate combines with coenzyme A to form acetyl coenzyme A (Acetyl CoA).

~ No ATP is produced.

Question 7

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

Answer 7

~ Every molecule of glucose produces 2x pyruvate molecules.

~ These reactions therefore occur 2x for every molecule of glucose.

Question 8

What Does Each Molecule Of Glucose Produce During The Link Reaction & Krebs Cycle?
(3 Points)

Answer 8

~ 2x molecules of acetyl CoA.

~ 2x molecules of CO2.

~ 2x molecules of reduced NAD.

Question 9

Describe The Krebs Cycle
(4 Points)

Answer 9

~ Involves a series of oxidation and reduction reactions.

~ Each of the reactions are controlled by a specific intracellular enzyme.

~ Take place on the matrix of the mitochondria.

~ Cycle happens for every pyruvate molecule, so it goes round 2x for every glucose molecule.

Question 10

Describe the Steps Of The Krebs Cycle
(8 Points)

Answer 10

~ Acetyl CoA (2C) enters the circular pathway from the link reaction in glucose metabolism.

~ Oxaloacetate (4C) accepts the acetyl (2C) fragment from acetyl CoA to form citrate (6C).

~ Coenzyme A goes back into the link reaction to be used again.

~ The citrate is converted into a 5C compound.

~ Decarboxylation and dehydrogenation occurs, where the hydrogen is used to produce reduced NAD from NAD.

~ Decarboxylation and dehydrogenation occur again, producing 1x of reduced FAD and 2x of reduced NAD.

~ This regenerates oxaloacetate.

~ ATP is produced by substrate linked phosphorylation.

Question 11

What Is Substrate Linked Phosphorylation Of The Krebs Cycle?

Answer 11

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

Question 12

What Are The Products Of The Krebs Cycle?
(4 Points)

Answer 12

~ 2x ATP.

~ 6x reduced NAD.

~ 2x reduced FAD .

~ 4x CO2.