Metabolism III

Question 1

What is the function of hexokinase at low glucose concentrations?

Answer 1

Sequesters glucose in the tissues (p.99)

Question 2

Where is excess glucose stored at high glucose concentrations?

Answer 2

In the liver (p.99)

Question 3

What is the net reaction for glycolysis?

Answer 3

Glucose + 2Pi +2ADP + 2NAD+ –> 2 pyruvate + 2ATP + 2NADH + 2H+ + 2H2O (p.100)

Question 4

Name the two reactions in glycolysis that require ATP.

Answer 4

1.) Glucose –> Glucose 6 phosphate (catalyzed by glucokinase/hexokinase); 2.) Fructose-6-P –> Fructose 1,6, BP (catalyzed by PFK1) (p.100)

Question 5

What two substrates inhibit hexokinase and glucokinase activity respectively?

Answer 5

Hexokinase- Glucose-6-P; Glucokinase- Fructose-6-P (p.100)

Question 6

Name the two reactions in glycolysis that produce ATP.

Answer 6

1,3-BPG –> 3-PG and its reverse reaction; PEP –> pyruvate (via pyruvate kinase) (p.100)

Question 7

What are the regulators of Pyruvate Kinase?

Answer 7

(+) Fructose-1,6-BP; (-) ATP, alanine

Question 8

Describe the feedback system of Fructose 2,6 bisphosphate on PFK-1.

Answer 8

Phosphofructokinase-2 is active in the fed state and catalyzes the reaction of fructose-6-phosphate to fructose-2,6-bisphosphate. Production of Fructose 2,6 bisphosphate catalyzes the reaction of Fructose-6-phosphate to Fructose1,6bisphosphate in glycolysis (p.100)

Question 9

What reaction is catalyzed by Fructose bisphosphatase-2?

Answer 9

Active in the fasting state, catalyzes Fructose 2,6-bisphosphate to Fructose-6-phosphate for gluconeogenesis (p.100)

Question 10

Describe the activity of FBPase-2 and PFK2 in the fasting state.

Answer 10

Increased glucagon –> increases cAMP –> increases protein kinase A –> increases FBPase-2 and decreases PFK2 to decrease glycolysis (p.100)

Question 11

Describe the activity of FBPase-2 and PFK2 in the fed state.

Answer 11

Increased insulin –> decreases cAMP –> decreases protein kinase A –> decreases FBPase-2 and increases PFK2 to increase glycolysis (p.100)

Question 12

What cofactors are needed for the reaction of pyruvate –> acetyl CoA?

Answer 12

Pyruvate + NAD+ + CoA –> AcetylCoA + CO2 + NADH (p.100)

Question 13

What five cofactors are required by the three enzymes of the pyruvate dehydrogenase complex?

Answer 13

1.) Pyrophosphate (B1, thiamine, TTP); 2.) FAD (B2, riboflavin); 3.) NAD (B3, niacin); 4.) CoA (B5, pantothenate); 5.) Lipoic acid (p.100)

Question 14

What changes occur to the pyruvate dehydrogenase complex in conditions of exercise?

Answer 14

Increased NAD+/NADH ratio; increased ADP, increased Ca2+ (p.100)

Question 15

What complex is very similar to the pyruvate dehydrogenase complex?

Answer 15

The alpha-ketoglutarate dehydrogenase complex; it has similar substrates and action and the same cofactors (p.100)

Question 16

What reaction does alpha-ketoglutarate dehydrogenase catalyze?

Answer 16

Conversion of alpha-ketoglutarate to succinyl CoA in the TCA cycle (p.100)

Question 17

What is the mechanism of action of arsenic poisioning?

Answer 17

Inhibition of lipoic acid (p.100)

Question 18

What are the principle symptoms of arsenic poisioning?

Answer 18

Vomiting, rice water stools, garlic breath (p.100)

Question 19

What is the principle symptom of a pyruvate dehydrogenase complex deficiency?

Answer 19

Neurologic defects, usually starting in infancy (p.101)

Question 20

Describe the pathology associated with a pyruvate dehydrogenase complex deficiency.

Answer 20

Backup of substrate (pyruvate and alanine) cause a lactic acidosis (p.101)

Question 21

Name the two purely ketogenic amino acids.

Answer 21

Lysine and Leucine (p.101)

Question 22

What is the genetic inheritance associated with a pyruvate dehydrogenase complex deficiency?

Answer 22

Most cases are due to mutations in X-linked genes for the E1-a subunit of PDC (p.101)

Question 23

How do you treat a pyruvate dehydrogenase complex deficiency?

Answer 23

Increase intake of ketogenic nutrients (e.g. high fat content or increase lysine and leucine) (p.101)

Question 24

Name the four products of pyruvate metabolism.

Answer 24

Alanine, Oxaloacetate, Acetyl-CoA, Lactate (p.101)

Question 25

What reaction does Alanine aminotransferase catalyze?

Answer 25

Converts pyruvate to alanine in the cytosol for the cahill cycle where Alanine carries amino groupt to the liver from muscle (p.101)