Citric Acid Cycle

Question 1

Define the Citric Acid Cycle

Answer 1

An amphibolic metabolic pathway that takes place in the mitochondrial matrix and has the main purpose of creating energy

Question 2

The CAC is a sequence of reactions that oxidize _____ to ____ and reduce coenzymes

Answer 2

Acetyl CoA; CO2

Question 3

Coenzymes are reoxidized via the ____

Answer 3

Electric Transport Chain

Question 4

The Citric Acid Cycle is the final common pathway for the oxidation of ____, ____, and ____ due to glucose, fatty acids, and most amino acids being metabolized to acetyl CoA or intermediates of the cycle

Answer 4

carbohydrate, lipid, and protein

Question 5

FIRST: Acetyl CoA + Oxaloacetate =

Enzyme Used:

Answer 5

Citrate

Enzyme: Citrate synthase

Question 6

Citrate is isomerized. The first step is dehydration to cis-aconitate (1/2) =

Answer 6

Cis-aconitate

Enzyme: Aconitase

Question 6

Isocitrate undergoes dehydration/dehydrogenation with isocitrate dehydrogenase =

Answer 6

Oxalosuccinate

Enzyme: Isocitrate Dehydrogenase

Question 6

Citrate is isomerized to isocitrate by aconitase. The second step is rehydration to isocitrate (2/2) =

Answer 6

Isocitrate

Enzyme: Aconitase

Question 7

Reaction: Oxalosuccinate undergoes decarboxylation to α-ketoglutarate =

Answer 7

α-ketoglutarate

Enzyme: Isocitrate Dehydrogenase

Question 7

Reaction: α-ketoglutarate undergoes oxidative decarboxylation =

Answer 7

Succinyl-CoA

Enzyme: α-ketoglutarate dehydrogenase complex

Question 8

Reaction: Loss of CoA, ATP gained, no O2 involved =

Answer 8

Succinate

Enzyme: Succinate Thiokinase

Question 9

Reaction that is the only example of substrate-level phosphorylation in the CAC

Answer 9

Succinyl-CoA —> Succinate (Succinate Thiokinase)

Question 10

Reaction: Succinate reduced to form FADH2 =

Answer 10

Fumarate

Enzyme: Succinate dehydrogenase (bound to inner mitochondrial membrane)

CAN BE INHIBITED WITH MALONATE

Question 11

Reaction: Hydration of Fumarate via Fumarase and converted to L-Malate =

Answer 11

L-Malate

Enzyme: Fumarase

Question 12

Last Reaction of the CAC

Start:
End:
Enzymes:

Answer 12

L-Malate
Oxaloacetate

Enzyme: Malate Dehydrogenase

Question 13

Isocitrate → Oxalosuccinate (Isocitrate Dehydrogenase product

Answer 13

NADH2

Question 14

α-Ketoglutarate → Succinyl CoA (α-Ketoglutarate Dehydrogenase Complex) product

Answer 14

NADH2

Question 15

Succinyl CoA → Succinate (Succinate Thiokinase) product

Answer 15

ATP

Question 16

Succinate → Fumarate (Succinate Dehydrogenase) product

Answer 16

FADH2

Question 17

L-Malate → Oxalacetate (Malate Dehydrogenase) product

Answer 17

NADH2

Question 18

(ONE TURN OF CAC) 1 NADH →

Answer 18

2.5 ATP

Question 19

(ONE TURN OF CAC) 1 FADH2→

Answer 19

1.5 ATP

Question 20

(ONE TURN OF CAC) Substrate Level Phosphorylation (Succinate Thiaminase) =

Answer 20

1 ATP

Question 21

4 Oxidative or Synthetic Processes in which CAC functions

Answer 21

• Transamination/Deamination
  a. Transfer amino group/taking it off and converted to ammonia, etc.
• Amino Acid Synthesis
• Gluconeogenesis
• Fatty Acid Synthesis

Question 22

Explain the connection(s) between the citric acid cycle and gluconeogenesis

Answer 22

a. All intermediates are potentially glucogenic (converted to glucose) Breakdown of large molecules, commonly involving oxidative reactions

Buildup of acetyl coA = Ketone body formation

Question 23

14. Explain the connection(s) between the citric acid cycle and FA synthesis

Answer 23

a. Fatty acid synthesis occurs in the cytosol.

b. Main substrate is acetyl coA.

i. Pyruvate → Pyruvate dehydrogenase → Acetyl CoA (occurs in mitochondria)

ii. Acetyl CoA → Citrate Synthase → Citrate (citrate can cross the mitochondrial membrane*

Question 24

______ has to be converted to _____ within the _____ to leave

Answer 24

Acetyl CoA ; citrate ; mitochondria

Question 25

Name the most highly-regulated enzymes of the citric acid cycle.

Answer 25

a. Citrate Synthase
b. Isocitrate Dehydrogenase
c. α-Ketoglutarate Dehydrogenase

Question 26

CASE STUDY: With what does fluoroacetate react to form fluorocitrate?

Answer 26

Fluoroacetate reacts with coenzyme A = fluroacetyl CoA

fluroacetyl CoA then reacts with oxaloacetate to make flurocitrate

Question 27

CASE STUDY: What metabolic pathway is inhibited by flurocitrate formation?

Answer 27

The citric acid cycle.

Flurocitrate inhibits aconitase from turning citrate into cis-aconitate. This leads to citrate accumulation.