TCA cycle

Question 1

What does each turn of the TCA cycle produce?

Answer 1

2 CO2 molecules = waste
3 NADH
1 GTP
1 FADH2

Question 2

What are the characteristics of Krebs cycle enzymes?

Answer 2

Soluble proteins located in mitochondrial matrix

Question 3

What conditions does TCA cycle operate and why?

Answer 3

Aerobic conditions

Re-oxidation of coenzymes needed to produce ATP, so FADH and NADH need to transfer their electrons in OP, if the next step doesn’t occur this can’t either

Question 4

What enters the TCA cycle?

Answer 4

When pyruvate is converted to to acetyl CoA, it combined with 4 carbon Oxaloacetate creating 6 carbon citrate

Amino acids can also enter the TCA cycle

Question 5

Why can amino acids be used in the TCA cycle?

Answer 5

Amino acid degradation involves breaking down the amino group which is excreted at urea

The carbon skeleton can then enter the TCA cycle or into the production of glucose

Question 6

What molecules are created from the degradation of all 20 amino acids?

Answer 6

7 molecules:

Pyruvate
Acetyl CoA
Acetocetyl CoA
a-ketoglutarate
succinyl CoA
Fumarate
Oxaloacetate

( all of which can be part of the krebs cycle )

Question 7

What does of reaction is a transamination reaction?

Answer 7

Group transfer ( between the amino and carboxyl group )

Question 8

What occurs in the reaction between

alanine + a-ketoglutarate –> ?

Answer 8

alanine + a-ketoglutarate –> pyruvate + glutamate

enzyme : alanine transferase

Then pyruvate can enter the TCA cycle

Question 9

How do NADH electrons cross from the cytosol into the mitochondria for OP in the skeletal muscle and brain ?

Answer 9

Glycerol phosphate shuttle

Question 10

How do NADH electrons cross from the cytosol into the mitochondria for OP in the liver, kidney and heart ?

Answer 10

Malate - aspartate shuttle

Question 11

Describe the steps in the glycerol phosphate shuttle?

Answer 11

• Cytoplasmic glycerol 3 phosphate dehydrogenase converts NADH –> NAD+ during the reaction between DHAP to glycerol 3 phosphate

The electrons now are in glycerol 3 phosphate

During the reaction of glycerol 3 phosphate back to DHAP , Mitochondrial glycerol 3 phosphate dehydrogenase converts FADH2 ( which was made from the reaction ) back to FAD

The electrons in FAD then get passed to co-enzyme Q, part of the electron transport chain

Question 12

How does the Malate Aspartate shuttle work?

Answer 12

Aspartate –> oxaloacetate ( aspartate transaminase )
oxaloacetate –> malate ( malate dehydrogenase )

The malate is then shuttled into the mitochondria

malate is then reversed to oxaloacetate and then aspartate ( NAD+ –> NADH) and ( glutamate –> a-ketoglutamate ) and same enzymes.

Aspartate removed with antiporter back out into the cycle.

Question 13

How many molecules of ATP is produced by the oxidation of 1 acetyl CoA?

Answer 13

3 NADH = 3 x 3 = 9
1 FADH = 1 x 2 = 2
+ 1 GTP

= 12 ATP

Question 14

What enzymes can become mutated to cause cancer?

Answer 14

These mutations decrease TCA activity and increase aerobic glycolysis leading to lactate - Warburg effect

Isocitrate dehydrogenase, succinate dehydrogenase, fumerase = activity is decreased when mutated