Citric Acid Cycle

Question 1

Net reaction of beta oxidation

Answer 1

16-C acyl + 7 CoA + 7 NAD+ + 7H20 + FAD -> 8 Acetyl CoA + 7NADH+ + 7H+ + FADH2

Question 2

How many high-energy phosphates are created per turn of the TCA cycle from NADH production?

Answer 2

3 NADH @ 2.5 ATP/NADH = 7.5

Question 3

How many high-energy phosphates are created per turn of the TCA cycle from FADH2 production?

Answer 3

1 FADH2 @ 1.5 ATP/FADH2 = 1.5

Question 4

How many high-energy phosphates are created per turn of the TCA cycle from GTP?

Answer 4

1 GTP per 1 ATP = 1

Question 5

Coarse control of the citric acid cycle

Answer 5

By levels of ADP; reoxidation of NADH and FADH2 is needed, which is coupled to ATP production. If there’s enough ATP, reoxidation will not occur and the CAC will slow

Question 6

Rate limiting of the CAC

Answer 6

Level of ADP

Question 7

Supply of acetyl CoA

Answer 7

Level of PDH activity and transport of fatty acids into the mitochondria

Question 8

What affects oxaloacetate levels?

Answer 8

Biosynthetic pathways that affect the concentration of CAC intermediates

Question 9

Fine control of the CAC

Answer 9

By allosteric inhibitors (negative feedback)

Question 10

Negative feedback on citrate synthase

Answer 10

Succinyl CoA

Question 11

Allosteric modifiers of isocitrate dehydrogenase

Answer 11

(+): ADP

(-): ATP and NADH

Question 12

Allosteric modifiers of alpha-ketoglutarate dehydrogenase

Answer 12

(+): Calcium

(-): GTP/ATP, succinyl coA, NADH

Question 13

In what other biosynthetic pathway is citrate involved?

Answer 13

Fatty acid/sterol synthesis

Question 14

In what other biosynthetic pathway is alpha-ketoglutarate involved?

Answer 14

Amino acid synthesis

Question 15

In what other biosynthetic pathway is succinyl CoA involved?

Answer 15

Heme production

Question 16

In what other biosynthetic pathway is malate involved?

Answer 16

Gluconeogenesis

Question 17

In what other biosynthetic pathway is oxaloacetate involved?

Answer 17

Amino acid synthesis

Question 18

Anaplerotic reactions

Answer 18

“Replenishing” reactions

Question 19

What replenishes AKG?

Answer 19

Amino acids -> glutamate

Question 20

What replenishes succinyl coA?

Answer 20

Valine and isoleucine -> propionyl coA

Question 21

What replenishes fumarate?

Answer 21

Amino acids

Question 22

What replenishes oxaloacetate?

Answer 22

Aspartate and pyruvate

Question 23

What replenishes pyruvate?

Answer 23

Amino acids

Question 24

Most common form of PDH deficiency

Answer 24

X-linked dominant mutation of the E1 domain of the enzyme (others are autosomal recessive)

Question 25

Signs of PDH deficiency

Answer 25

Increased plasma levels of pyruvate, lactate, and alanine, which produce a lactic acidosis

Question 26

Treatment of PDH deficiency

Answer 26

Dietary supplementation of thiamine, carnitine, and lipoic acid

Question 27

Inheritance of fumarase deficiency

Answer 27

Autosomal recessive disorder that is extremely rare

Question 28

Symptoms of fumarase deficiency

Answer 28

Neurologic impairment, encephalopathy, and dystonia that develops shortly after birth
Urine high in fumarate, succinate, AKG, citrate, and malate

Question 29

Treatment of fumarase deficiency

Answer 29

There is no effective treatment currently

Question 30

Fluorocitrate

Answer 30

Inhibits aconitase and therefore the CAC; used as rat poison