Cell Metabolism 2 - Tricarboxylic Acid Cycle

Question 1

Products of the Kerbs/TCA cycle

Answer 1

2x CO2

3x NADH

1x GTP

1x FADH2

Question 2

Where is the Krebs/TCA cycle located?

Answer 2

Mitochondrial matrix space

Question 3

When is the bulk of ATP generated?

Answer 3

When reduced coenzymes are re-oxidised

Question 4

Step 1:How does the Krebs/TCA cycle start?

Answer 4

Acetyl CoA joins with oxoaloacetate —> makes citrate

Condensation of 4C + 2C

Question 5

Step 2: what happens to citrate

Answer 5

Isomerise to isocitrate

Question 6

Step 3: what happens to the isocitrate?

Answer 6

Isocitrate —> alpha ketoglutarate

Decarboxylation

Removes e- —> added to NAD+ to form NADH

Question 7

Step 4: what happens to alpha-ketoglutarate?

Answer 7

Alpha-ketoglutarate —> succinyl-CoA

Decarboxylation

Removes e- —> added to NAD+ to form NADH

Question 8

Step 5: what happens to succinyl CoA?

Answer 8

Succinyl CoA —> succinate

Removes CoA-SH
GDP + Pi —> GTP

Question 9

Step 6: what happens to succinate?

Answer 9

Succinate —> fumerate

Removes e- —> added to FAD —> FADH

Question 10

Step 7: what happens to fumerate?

Answer 10

Fumerate —> malate

Hydration

Question 11

Step 8: what happens to malate?

Answer 11

Malate —> oxoloacetate

Removes e- —> NAD+ —> NADH

Question 12

What does oxaloacetate do?

Answer 12

Joins with another acetyl CoA

Question 13

Why is FAD used rather than NAD?

Answer 13

Free energy change is only enough to be able to reduce FAD

FAD has a greater affinity to the e-

Question 14

What two types of amino acids enter the TCA cycle?

Answer 14

Glucogenic

Ketogenic

Question 15

What happens to an amino acid before it is fed into the TCA cycle?

Answer 15

Amino acid removed —> excreted as urea

Carbon skeleton funnelled into the the TCA cycle

Question 16

What is transamination?

Answer 16

Amine group is transferred from one amino acid to a keto acid

Group transfer

Question 17

Alainine transamination

Answer 17

Alanine + alpha-ketoglutarate —> pyruvate + glutamate

Glutamate re-converted into alpha-ketoglutarate by glutamate dehydrogenase

Question 18

How many ATP does NADH, FADH, GTP?

Answer 18

3
2
1

Question 19

How does NADH (its high energy e-) cross from the cytoskeleton into the mitochondria matrix?

Answer 19

Glycerol phosphate shuttle

Malate-aspartame shuttle

Question 20

What happens in the glycerol phosphate shuttle?

Answer 20

Dihydroxyacetone phosphate converted into glycerol 3-phosphate

NADH transfers e- to DHAP

Membrane bound glycerol 3-phosphate transfers e- to FAD to from FADH2

Question 21

Where does the glycerol phosphate shuttle occur?

Answer 21

Muscle

Brain

Question 22

What happens in the malate-aspartate shuttle?

Answer 22

Aspartate ate converted into oxoalacetate ( transamination)

Oxoalacetate converted into malate

NADH gives e- to malate

Malate diffuses through the mitochondrial matrix

Reverse reactions happen

NAD+ —> NADH

Question 23

Where does the malate-aspartate shuttle occur?

Answer 23

Liver

Heart

Kidney

Question 24

How many ATPs does the oxidation of 1x acetyl CoA give?

Answer 24

3x NADH (3x3)

1x FADH2 (1x2)

1x GTP

(3x3) + (1x2) + 1 = 12 ATP

Question 25

What do mutations in the TCA cycle genes cause?

Answer 25

Decrease TCA activity and enhance aerobic glycolysis (Warburg Effect)