18.2 Link Reaction / Oxidative Decarboxylation

Question 1

What is the role of the link reaction/ oxidative decarboxylation?

Answer 1

links glycolysis, which occurs in the cytoplasm

to Kreb’s cycle, which occurs in the mitochondrial matrix

Question 2

Where does the link reaction take place?

Answer 2

mitochondrial matrix

(pyruvate from glycolysis acts as reactant in link reaction, so must be actively transported into mitochondria)

Question 3

Outline the steps of the link reaction/oxidative decarboxylation:

Answer 3

1. Pyruvate from glycolysis actively transported into mitochondrial matrix using carrier proteins
2. pyruvate undergoes decarboxylation (removal of CO2)
3. NAD oxidises by removing hydrogen, NAD + pyruvate ⟶ NADH + Acetyl group
4. Acetyl group + Coenzyme A ⟶ Acetyl coenzyme A,

Acetyl coenzyme A delivers acetyl group to Kreb’s cycle

Question 4

How does acetyl coenzyme A act as a coenzyme during the link reaction?

Answer 4

transfers group of atoms from 1 reaction to another in a multi-step pathway:

coenzyme A accepts acetyl group during oxidative decarboxylation

supplies it to a later stage during Kreb’s cycle

Question 5

What is the function of the outer mitochondrial membrane?

Answer 5

allows for compartmentalisation

by separating mitochondrion from rest of cell

Question 6

What is the function of the inner mitochondrial membrane?

Answer 6

contains electron transport chains & ATP synthase membrane proteins

for chemiosmosis

Question 7

What are cristae & what is their function?

Answer 7

projections of inner membrane

increases surface area over which oxidative phosphorylation can occur

Question 8

What is the function of the intermembrane space in mitochondria?

Answer 8

gap where protons are pumped into by electron transport chain

small, so used to create high concentrations of molecules

Question 9

What is the function of the mitochondrial matrix?

Answer 9

contains mitochondrial DNA, & enzymes

for Kreb’s cycle & link reaction

Question 10

____ + Coenzyme A + NAD ⟶ ____ + CO₂ + ____

Answer 10

pyruvate, acetyl coenzyme A, NADH

Question 11

Link reaction / Oxidative decarboxylation

What occurs to oxidise the pyruvate molecule?

Answer 11

removal of hydrogen atom

(hydrogen removed by NAD, forming NADH)

Question 12

Pyruvate is a product of glycolysis, which occurs in the cytoplasm.

How does it enter the mitochondrial matrix to be processed in the link reaction?

Answer 12

via active transport

using specific carrier proteins

Question 13

Pyruvate + Coenzyme A + NAD ⟶

Answer 13

Acetyl coenzyme A, NADH, CO₂

Question 14

What can occur to the CO₂ removed during oxidative decarboxylation?

Answer 14

• diffuse into bloodstream & removed as waste
• used for photosynthesis in autotrophs