TCA cycle

Question 1

What are the 3 stages of the TCA cycle?

Answer 1

Acetyl CoA production
Acetyl CoA oxidation
Electron transfer and oxidative phosphorylation

Question 2

Where in teh cell does the TCA cycle occur?

Answer 2

The matrix of the mitochondria

Question 3

How is citrate formed?

Answer 3

Acetyl CoA joins with oxaloacetate to form citrate

Question 4

How many redox reactions occur per turn of the cycle?

Answer 4

4

Question 5

How many NADH molecules are produced per cycle?

Answer 5

3

Question 6

How many FADH molecules are produced per cycle?

Answer 6

1

Question 7

What are the functions of the TCA cycle?

Answer 7

Metabolism of all fuels
Participates in gluconeogenesis
Provides energy and metabolites for cell metabolism
Conversion of carbohydrates to fat
Source of non-essential amino acids (E&D)

Question 8

What enters the TCA cycle?

Answer 8

Acetyl CoA

Question 9

What is acetyl CoA the end product of?

Answer 9

Glycolysis
Beta-oxidation
Amino acid catabolism

Question 10

What enzyme catalyses oxidative decarboxylation of pyruvate?

Answer 10

Pyruvate dehydrogenase

Question 11

What does the oxidative decarboxylation of pyruvate form?

Answer 11

CoEnzyme A

Question 12

What 5 coenzymes are needed for the oxidative decarboxylation of pyruvate?

Answer 12

TPP
Lipoyllysine
FAD
NAD
Acetyl CoA

Question 13

What does Coenzyme A do?

Answer 13

Carries acyl groups and thioesters

Question 14

What does high [ATP] mean?

Answer 14

Energy needs of the cell are being met

Question 15

What does high [pyruvate] mean?

Answer 15

Cell requires energy

Question 16

What steps of oxidative decarboxylation of pyruvate are regulated by enzyme 1?

Answer 16

Decarboxylated of pyruvate to an aldehyde
Oxidation of the aldehyde to a carboxylic acid

Question 17

What steps of oxidative decarboxylation of pyruvate are regulated by enzyme 2?

Answer 17

Formation of acetyl CoA

Question 18

What steps of oxidative decarboxylation of pyruvate are regulated by enzyme 3?

Answer 18

Reoxidation of lipoamide cofactor
Regeneration of the oxidised FAD cofactor - NADH produced

Question 19

How is the condensation of oxaloacetate with acetyl CoA regulated?

Answer 19

Tightly, controlled step which is required for the cycle

Question 20

What are the intermediates of the TCA cycle?

Answer 20

Citrate
Isocitrate
Alpha-ketoglutarate
Succinyl CoA
Succinate
Fumarate
L-Malate
Oxaloacetate

Question 21

What step(s) result in decarboxylation and NADH production?

Answer 21

Isocitrate to alpha-ketoglutarate
Alpha-ketoglutarate to succinyl CoA

Question 22

What happens during the conversion of succinyl CoA to succinate?

Answer 22

Substrate level phosphorylation forming GTP

Question 23

What step produces FADH2?

Answer 23

Succinate to fumarate

Question 24

What step results in ONLY the production of NADH?

Answer 24

L-malate to oxaloacetate

Question 25

What does high citrate concentrations mean?

Answer 25

Cell energy requirements are met

Question 26

What does the activity of the TCA cycle depend on?

Answer 26

Availability of NAD+ for the dehydrogenase reaction Oxaloacetate and citrate concentrations Pyruvate dehydrogenase activity Citrate synthase activity Isocitrate dehydrogenase activity Alpha-ketoglutarate dehydrogenase activity

Question 27

What is the general regulatory mechanisms of the TCA cycle?

Answer 27

Activated by substrate availability Inhibited by product accumulation NADH and ATP inhibit NAD+ and ADP activate

Question 28

What is the general regulatory mechanisms of the TCA cycle?

Answer 28

Activated by substrate availability Inhibited by product accumulation NADH and ATP inhibit NAD+ and ADP activate

Question 28

What is the general regulatory mechanisms of the TCA cycle?

Answer 28

Activated by substrate availability Inhibited by product accumulation NADH and ATP inhibit NAD+ and ADP activate

Question 29

What is needed for dehydrogenase reactions?

Answer 29

NAD+

Question 30

What does citrate synthase do?

Answer 30

Converts oxaloacetate and acetyl CoA to citrate

Question 31

What happens to citrate synthase during fasting?

Answer 31

[ATP] and [NADH] increase Equilibrium between L-malate: oxaloacetate pushes towards L-malate Malate is used for gluconeogenesis in cytosol Acetyl CoA used for ketone synthesis due to lack of oxaloacetate

Question 32

What kind of enzymes regulate the TCA cycle and what are their names?

Answer 32

Exergonic Citrate synthase Isocitrate dehydrogenase Alpha-ketoglutarate dehydrogenase

Question 33

What are the enzymes regulating the TCA cycle regulated by?

Answer 33

Energy indicators Product accumulation Substrate availability

Question 34

What downregulates pyruvate dehydrogenase?

Answer 34

Pyruvate dehydrogenase kinase

Question 35

What activates pyruvate dehydrogenase kinase?

Answer 35

Acetyl CoA NADH

Question 36

What inactivates pyruvate dehydrogenase kinase?

Answer 36

Pyruvate ADP Ca++ K+

Question 37

What upregulates pyruvate dehydrogenase?

Answer 37

Pyruvate dehydrogenase phosphatase

Question 38

What activates pyruvate dehydrogenase phosphatase?

Answer 38

Ca++ Mg++

Question 39

Where is isocitrate dehydrogenase found in the cell?

Answer 39

Cytosol Mitochondria

Question 40

What inhibits isocitrate dehydrogenase?

Answer 40

ATP & NADH

Question 41

What stimulates isocitrate dehydrogenase?

Answer 41

ADP, NAD+, Ca++

Question 42

How does isocitrate dehydrogenase behave in the absence of ADP?

Answer 42

Basically inactive

Question 43

What happens due to isocitrate dehydrogenase?

Answer 43

Decarboxylation NADH production

Question 44

What stimulates alpha-ketoglutarate dehydrogenase?

Answer 44

Ca++

Question 45

What inhibits alpha-ketoglutarate dehydrogenase?

Answer 45

ATP Succinyl CoA NADH

Question 46

What occurs due to the activity of alpha-ketoglutarate dehydrogenase?

Answer 46

Decarboxylation NADH produced

Question 47

How are 4 carbon intermediates formed?

Answer 47

Carboxylation of 3 carbon precursors