TCA cycle

Question 1

Where does glycolysis, pyruvate processing, TCA cycle and ETC happen?

Answer 1

glycolysis: cytoplasm
pyruvate processing & TCA cycle: mitochondrial matrix ETC: inner membrane

Question 2

What is cristae?

Answer 2

extensions of inner membrane
layers of sac like structures.
fill inside of mitochondria.
are connected to inner membrane by short tube

Question 3

under hypoxic or anaerobic, what happens to pyruvate?

Answer 3

fermentation into ethanol or lactate

Question 4

under aerobic conditions, what happens to pyruvate?

Answer 4

pyruvate –> acetyl-Coa –> produces CO2 and water

Question 5

5 coenzymes required for pyruvate processing?

Answer 5

TPP
Lipoyl lisine (lipoamide)
FAD
NAD+
CoA-SH

Question 6

Pyruvate processing catalyzed by which enzyme?

Answer 6

Pyruvate dehydrogenase complexe

Question 7

Which 3 enzymes for pyruvate processing?

Answer 7

Pyruvate dehydrogenase
Dihydrolipoyl transacetylase
Dihydrolipoyl dehydrogenase

Question 8

Pyruvate processing regulated by what?

Answer 8

Feedback inhibition: if products of glycolysis or pyruvate are abundant –> PDH is phosphorylated and inhibited through change in conformation

Question 9

5 steps of pyruvate processing

Answer 9

1. decarboxylation of pyruvate to aldehyde
2. oxidation of aldehyde into carboxylic acid –> electrons reduce lipoamide to form thioester
3. formation of acetyl-coA
4. Reoxidation of lipoamide cofactor
5. Regeneration of oxidized FAD cofactor –> forms NADH

Question 10

FAD with which enzyme?

Answer 10

Dihydrolipoyl dehydrogenase

Question 11

TPP with which enzyme?

Answer 11

Pyruvate dehydrogenase

Question 12

Lipoyl lysine with which enzyme?

Answer 12

Dihydrolipoyl transacetylase

Question 13

NAD and CoA-SH in which steps of pyruvate processing?

Answer 13

NAD in step 5 + CoA-SH in step 3

Question 14

Does coenzyme A stay on enzyme’s structure?

Answer 14

No. associate, fulfill function, dissociate

Question 15

Function of Coenzyme-A?

Answer 15

accept and carry acetyl groups –> carries remaining carbons from glucose to TCA cycle to be further oxidized

Question 16

Multiple intermediates from CAC can be used as reactants in other metabolic pathways –> name?

Answer 16

Anaplerotic reactions

Question 17

CAC = amphibolic?

Answer 17

Involves both catabolism and anabolism

Question 18

Why anaplerotic reactions?

Answer 18

To replenish depleted cycle intermediates

Question 19

4 enzymes for anaplerotic reactions

Answer 19

pyruvate carboxylase
PEP carboxykinase (CO2 and GDP)
PEP carboxylase (HCO3-)
malic enzyme (pyruvate + HCO3- + NAD(P)H)

Question 20

first substrate of TCA cycle? how many carbons?

Answer 20

Acetyl-CoA –> 2C

Question 21

Rate limiting step of CAC cycle?

Answer 21

Step 1: citrate synthesis

Question 22

What does step 1 of TCA largely depend on?

Answer 22

Oxaloacetate concentration

Question 23

acetyl-CoA + oxaloacetate –> citrate

Answer 23

Step 1. Citrate synthase. F + I

Question 24

citrate –> isocitrate (passing through what?) + rationale?

Answer 24

passing through cis-aconitate. Step 2. Aconitase. U + R. secondary alcohol is a better substrate for oxidation

Question 25

Isocitrate --> alpha-ketoglutarate

Answer 25

Step 3. isocitrate dehydrogenase. decarboxylation. produces NADH and CO2. F + I

Question 26

alpha-ketoglutarate --> succinyl-CoA

Answer 26

Step 4. Alpha-ketoglutarate dehydrogenase. F + I. produces NADH and CO2

Question 27

Succinyl-CoA --> Succinate

Answer 27

Step 5. Substrate level phosphorylation. Succinyl-CoA synthetase. produces GTP. F + R

Question 28

Succinate --> fumarate

Answer 28

Step 6. Alkane to alkene. Succinate dehydrogenase (bound to inner membrane, act as complex II in ETC). equilibrium + R

Question 29

Fumarate --> L-malate

Answer 29

Step 7. Fumarase. water added (OH- and H+), always trans --> intermediate of carbanion. F + R

Question 30

L-malate --> oxaloacetate

Answer 30

Step 8. L-malate dehydrogenase. U + R. produces NADH!

Question 31

Which steps of TCA produce NADH?

Answer 31

Steps 3, 4 and 8. (2 decarboxylation and one during regeneration of oxaloactate)

Question 32

Which step of TCA produces FADH2?

Answer 32

Step 6. succinate to fumarate

Question 33

Which enzyme is similar to the pyruvate dehydrogenase complex?

Answer 33

alpha-ketoglutarate complex. same enzymes and mechanism but active sites different to accommodate different sized substrate

Question 34

Which molecule is has a high-energy thioester bond just like acetyl-CoA?

Answer 34

Succinyl-CoA

Question 35

When is there a net full oxidation of all glucose carbons?

Answer 35

Step 4 of TCA cycle. after 2nd decarboxylation --> forming succinyl-CoA

Question 36

What is formed at the end of TCA cycle?

Answer 36

2 CO2 + 3 NADH + FADH2 + GTP + CoA + 3 H+

Question 37

What is used during the TCA cycle?

Answer 37

1 Acetyl-CoA + 3 NAD+ + FAD+ + GDP + Pi + 2 H2O

Question 38

How many ATP produced after 1 glucose passes through TCA cycle?

Answer 38

21 ATP (10.5 per turn) NADH --> 2.5 each FADH2 --> 2 each GTP --> 1 each

Question 39

Energy of which oxidations conserved to reduce NAD+, FAD+ and GDP?

Answer 39

Of step 3 and 4. both decarboxylations by isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase

Question 40

Which reaction is an isomerization in TCA cycle?

Answer 40

step 2: citrate to isocitrate catalyzed by aconitase

Question 41

Which step is a condensation reaction in TCA cycle?

Answer 41

Step 1: Oxaloacetate + acetyl-CoA --> citrate. by citrate synthase

Question 42

Which steps are oxidation reactions in TCA cycle?

Answer 42

Steps 3, 4, 6 and 8

Question 43

Which step is a hydration reaction in TCA cycle?

Answer 43

Step 7. fumarate to L-malate by fumarase

Question 44

Which step is a substrate level phosphorylation in TCA cycle?

Answer 44

Step 5. Succinyl-CoA to succinate