Citric Acid Cycle

Question 1

What type of pathway is the citric acid cycle?

Answer 1

Catabolic and anabolic

Question 2

Where does the citric acid cycle occur?

Answer 2

In the mitochondria.

Question 3

The addition of which group led to the name of acetyl CoA?

Answer 3

The addition of a covalently bound acetyl group making a thiol bond.

Question 4

What is CoA in the acetyl coA molecules?

Answer 4

It is an energy carrier.

Question 5

Is there a lot of energy in the acetyl CoA molecule and the attachment of which group makes it ‘activated for transfer for acetyl groups and metabolism?

Answer 5

High energy.

Acyl group attached to CoA = ‘activated for transfer’ for acetyl groups in metabolism.

Question 6

What is acetyl coA?

Answer 6

It is an essential metabolite that fuels the citric acid cycle to direct end-product of fatty acid and amino acid catabolism.

Question 7

How is pyruvate able to enter the mitochondria to participate in the citric acid cycle?

Answer 7

In the presence of O2 via Mitochondrial Pyruvate Carrier Protein.

Question 8

Which enzyme is used to convert pyruvate to Acetyl-CoA?

Answer 8

Pyruvate dehydrogenase.

PDH

Question 9

What is the pyruvate dehydrogenase enzyme doing to pyruvate to catalyse it to become acetyl CoA?

Answer 9

oxidising and decarboxylating it

Occurs in the mm of eukaryotes.

Question 10

How many copies of enzyme subunits are needed for the conversion of pyruvate to acetyl coA?

Answer 10

multiple copies of 3 enzyme subunits.

E1, E2, E3

Question 11

Can PDH be seen using an electron microscope?

Answer 11

Yes

Question 12

Describe the regulation of converting pyruvate to acetyl coA?

Answer 12

• strong regulation
• allosteric
• covalent phosphorylation

Question 13

When is PDH off?

Answer 13

When there is ample fuel available and when cell’s energy is low.
Mutations in PDH genes or thiamine.

Question 14

What is an essential enzyme cofactor associated with the regulation of PDH?

Answer 14

Thiamine.

Question 15

What happens when pyruvate cannot be converted?

Answer 15

Energy dysfunction = brain damage ex:thiamine deficiency.

Question 16

What did Hans Krebs discover?

Answer 16

That certain organic acid anions stimulated pyruvate oxidaton.

Question 17

What were the organic acid anions what Krebs discovered that stimulated pyruvate oxidation?

Answer 17

1. Dicarboxylic acids COO- x2

2. TRicarboxylic acids COO- x3

Question 18

What is the start/end product of the Krebs cycle?

Answer 18

4C Oxaloacetate.

Question 19

What does the first 1-3 steps of the citric acid cycle involve?

Answer 19

4C oxaloacetate + 2C acetyl group of acetyl coA condense to form 6C citrate.
= 3 x COO- tricarboxylic acid.

Question 20

what does the 3- end of the citric acid cycle involve?

Answer 20

6C citrate (high energy reduced biomolecule) = oxidised and decarboxylated back to 4C oxaloacetate loses Hs with its electrons which collect on 3NADH and 1NADH2

Question 21

What is the production of a full citric acid cycle for one acetyl CoA condensation with oxaloacetate?

Answer 21

3 NADH
1 FADH
1 GTP
2 CO2

Question 22

How is acetyl group fed into the citric acid cycle?

Answer 22

Through combination with oxaloacetate.

Question 23

What is the waste product of the citric acid cycle?

Answer 23

2 carbons.

Question 24

Is the energy of oxidation conserved?

Answer 24

Yes it is so far for 1 acetyl CoA input/

Question 25

What is the most common type of enzyme used in the citric acid cycle?

Answer 25

Dehydrogenase

Question 26

Describe the claisen condensation?

Answer 26

This is where acetyl coA condenses with oxaloacetate (4C) to form (6C) citrate through the enzyme citrate synthase. High energy nature citrate Strong oxidation potential

Question 27

What is the sentence to remember the enzymes in

Answer 27

Our City Is Kept Safe From Mobsters

Question 28

Is the energy in the citric acid cycle conserved?

Answer 28

Yes, 3 NADH, 1 FADH, 1 GTP

Question 29

What can happen to the anabolic/biosynthetic pathways of the citric acid cycle?

Answer 29

These intermediates can be 'siphoned off'

Question 30

What are oxaloacetate and alpha ketoglutarate produced from?

Answer 30

Amino acid catabolism of aspartate and glutamate.

Question 31

What do anaerobic bacteria use the citric acid cycle for?

Answer 31

They have many enzymes/intermediates. Used for biosythesis.

Question 32

What does the anaerobic bacteria citric acid cycle lack?

Answer 32

Lacks alpha-ketogluterate - so they do not have a functioning catabolic cycle.

Question 33

Anaerobic bacteria use the citric acid cycle for biosynthesis, what does this indicate?

Answer 33

That the pathway evolved from an anabolic to both an anabolic and catabolic pathway when O2 became available.

Question 34

Which metabolites of the citric acid cycle can alter the response of both the innate and adaptive immune response?

Answer 34

Acetyl CoA, succinate and fumarate.

Question 35

In tumour formation what builds up?

Answer 35

Succinate dehydrogenase is inhibited = succinate build up. Tumour can progress more - cancer cells proliferate.

Question 36

Why is it important to have synthetic precursors - to have a synthetic system?

Answer 36

When T cells are proliferating to activate certain responses.

Question 37

What can build up of succinate and fumarate do?

Answer 37

these are oncometabolites that can promote tumorigenesis.

Question 38

What can succinate do when it leaves the mitochondria?

Answer 38

It can degrade to acetyl coA and oxaloacetate where acetyl coA can acetylate histones/regulate gene expression

Question 39

What are the 3 exergonic irreversible enzymes involved in the regulation of the cirtic acid cycle?

Answer 39

Citrate synthase Isocitrate dehydrogenase Alpha-ketoglutarate dehydrogenase Regulation of pyruvate dehydrogenase is also imortant

Question 40

How are the 3 exergonic irreversible enzymes of the citric acid cycle regulated?

Answer 40

Allosterically by - energy indicators (high energy NADH, ATP at high conc the enzymes turn off and vice versa) - product accumulation - substrate availability

Question 41

Why is the citric acid cycle known as the 'hub' of metabolism?

Answer 41

Because it is amphibolic (both catabolism and anabolism)