TCA Cycle

Question 1

What does Pyruvate dehydrogenase (PDH) do?

Answer 1

catalyses oxidative decarboxylation of pyruvate to acetyl-CoA
I t is a multienzyme complex with 3 enzymes
30 Enzyme 1 dimers
60 E2 monomers
6 E3 dimers
lipoic acid (lipoate) and thiamine pyrophosphate (TPP) prosthetic groups
5 times bigger than ribosomes

for substrate channeling
increases rate, less side reactions, coordinated control

Question 2

What property does the TCA cycle have and where does is occur?

Answer 2

amphibolic
in the mitochondrial matrix

Question 3

Where is Coenzyme A derived from?

Answer 3

derived from pantothenate (a vitamin), cysteine (an amino acid) and AMP

Question 4

What is Fluoroacetate

Answer 4

highly toxic-(LD50 = 0.2 mg kg-1 for rats)
leaves of some plants
toxin is fluorocitrate
inhibits aconitase
lethal synthesisor suicide inhibition

Question 5

How many carbons are there in the substrates and product of this reaction?

Answer 5

6

Question 6

How many carboxylic acid groups are there in citrate?

Answer 6

3

Question 7

isocitrate dehydrogenase, irreversible step
What type of reaction is this?

Answer 7

oxidative (due to NAD+) decarboxylation

Question 8

succinyl-CoA synthetase
succinyl-CoA converted to succinate. What are the other products?

Answer 8

GTP and coA-SH
ATP and GTP catalyse phosphate transfer which is an example of substrate-level phosphorylation.
Nucleoside diphosphate kinase moves the phosphate from GTP to ADP to make ATP.

Question 9

succinate dehydrogenase (complex II) redox reaction
What is being reduced?

Answer 9

coenzyme Q it is an integral protein found in the inner mitochondrial membrane

Question 10

fumarase (fumarate hydratase)
hydration of fumarate –> malate
malate dehydrogenase
oxidation by NAD+
What is the function of reaction 8?

Answer 10

To restart the cycle and prevent the build up of unwanted molecules (fumarate/malate)

Question 11

What is the Arnon-Buchanan cycle

Answer 11

Some bacteria may use this cyle which is the TCA cycle in reverse