Carbohydrate Metabolism

Question 1

Where does glycolysis occur?

Answer 1

In the Cytosol of all mammalian cells

Question 2

What is the substrate in glycolysis?

Answer 2

Glucose

Question 3

What are the end products in glycolysis?

Answer 3

2 molecules of either:
1. Pyruvate
2. Lactate

Question 4

Name the rate limiting enzyme in glycolysis?

Answer 4

Phosphofructokinase-1

Question 5

Metabolic Process that is promoted by insulin.

Answer 5

Glycogenesis

Question 6

Metabolic pathway that is responsible for maintenance of a normal serum glucose concentration in a patient rescued from being trapped under rubble in a building for 4 days.

Answer 6

Gluconeogenesis

Question 7

What is the reverse process of glycolysis?

Answer 7

Gluconeogenesis

Question 8

The immediate donor of the phosphoryl group to ADP in the production of ATP during glucose metabolism in erythrocytes.

Answer 8

Phosphoenolpyruvate

Question 9

Reaction that is unique to gluconeogenesis

Answer 9

Oxaloacetate phosphoenolpyruvate

Question 10

What is the rate limiting enzyme of gluconeogenesis?

Answer 10

Fructose-1,6-biphosphatase

Question 11

Differentiate Hexokinase vs Glucokinase

Answer 11

Hexokinase
1. Present in most tissues
2. Can phosphorylate glucose & other hexoses
3. Inhibited by glucose-6-P
4. Low km
5. Low Vmax
6. High affinity
Glucokinase
1. Present only in liver parenchymal cells, Islets cells of the pancreas
2. Can phosphorylate glucose & other hexoses
3. Inhibited by frucose-6-P
4. High Km
5. High Vmax
6. Low affinity

Question 12

Identify the 2 steps in glycolysis which produce ATP via substrate level phosphorylation.

Answer 12

1. 1,3-Biphosphoglycerate to 3-Phosphoglycerate
   (Enzyme: Phosphoglycerate kinase)
2. Phosphoenolpyruvate to Pyruvate
   (Enzyme: Pyruvate kinase)

Question 13

What is the end product of anaerobic glycolysis?

Answer 13

Lactate

Question 14

1 NADH = ____ ATP

Answer 14

2.5 ATPs

Question 15

1 FADH2 = _______ ATP

Answer 15

1.5 ATP

Question 16

Malate aspartate shuttle is primarily seen in which tissues?

Answer 16

Heart muscles & Most tissues

Question 17

What enzyme joins monosaccharides to form a disaccharide?

Answer 17

Glycosyltransferase

Question 18

How does the cell ensure that the glucose taken by GLUT remains inside rather than diffusing back out?

Answer 18

Hexokinases irreversibly catalyze the phosphorylation of intracellular glucose to glucose 6-P

Question 19

How does insulin signaling effect the activity of PFK-1?

Answer 19

Insulin signaling activates PFK-1 activity

Question 20

What is the significance of 2,3-BPG ?

Answer 20

1. Important allosteric effector of Hb
2. It decreases the affinity of Hb for Oxygen , thereby increasing O2 delivery to tissues

Question 21

Why does a deficiency in PDHC activity cause lactic acidosis?
( Pyruvate Dehydrogenase Complex)

Answer 21

Deficiency results to:
1. Rise in pyruvate
2. Upregulate other reactions of pyruvate metabolism such as reduction to lactate by NADH-requiring LDH leading to lactic acidosis

Question 22

Which Step in Citric Acid Cycle generates GTP?

Answer 22

Substrate -level phophorylation of GDP to GTP occuRs during the conversion of Succinyl coA to Succinate via cleavage of the high energy thioester bond in succinyl coA

Question 23

What are the major TCA cycle regulation sites?
What are the effectors?

Answer 23

The major sites of cycle regulation:
1.Citrate Synthase - Inh by Citrate, its product.
2. Isocitrate dehydrogenase - Inh by NADH & ATP; Activated by ADP & Calcium
3. Alpha-KGD Complex - Inh by NADH & Succinyl CoA ; Activated by Calcium

Question 24

What other substrates can be used in gluconeogenesis?

Answer 24

1. Glycerol
2. Pyruvate
3. Alpha-keto acids generated by the degradation of glucogenic amino acids produced from muscle proteolysis

Question 25

Is gluconeogenesis an endergonic or exergonic process?

Answer 25

Endergonic - uses energy from ATP and GTP hydrolysis

Question 26

In what 2 tissues and in what subcellular locale is glycogen stored?

Answer 26

Glycogen a branched homopolymer of glucose is stored in the cytosol of liver and muscle cells primarily.

Question 27

What is the role of glucose 6- phosphatase in glycogenolysis?

Answer 27

hydrolyzes glucose 6-p in the liver and the kidneys, generating free glucose that enter the blood stream

Question 28

Is the rate of fructose metabolism faster or slower than of glucose?

Answer 28

Fructose metabolism is faster because it bypasses the key rate-limiting enzyme of glycolysis , PFK-1 .

Question 29

What is the fate of the ribulose 5-P product of the oxidative reactions?

Answer 29

The ribulose-P can be reversibly isomerized to ribose 5-P and used in Purine and Pyrimidine nucleotide synthesis & xylulose 5-P that is used in sugar interconversions.

Question 30

Andersen disease is a deficiency of which enzyme?

Answer 30

Branching enzyme

Question 31

Hers disease is a deficiency of which enzyme?

Answer 31

Liver phosphorylase

Question 32

Pompe Disease is deficiency of which enzyme?

Answer 32

Lysosomal acid maltase

Question 33

Enzyme deficient in a infant presenting with vomiting, night sweats, tremors after ingesting fruit juices with positive reducing sugar in urine but negative for glucose.

Answer 33

Aldolase B deficiency- Hereditary Fructose Intolerance

Question 34

Characteristics of this step in glycolysis catalyzedd by phosphofructokinase and gluconeogenesis by fructose-1,6-biphosphatase?

Answer 34

Phosphofructokinase is inhibited more or less completely by physiologic concentrations of ATP

Question 35

This is the most common disease producing enzyme abnormality in humans

Answer 35

Glucose-6-Phosphate Dehydrogenase Deficiency

Question 36

This transporter on the luminal side of enterocytes absorbs glucose or galactose.

Answer 36

SGLT1

Question 37

Effects of insulin on GLUT4 transporter resulting in reduced serum glucose ?

Answer 37

It promotes GLUT 4 mobilization to the plasma membrane

Question 38

Among the transporters, only which requires insulin?

Answer 38

GLUT-4

Question 39

This type of glucose transporter is found within the small intestine and spermatocytes.

Answer 39

GLUT-5

Question 40

Ability to produce lactose in breastmilk of a female with classic galactosemia due to GALT deficiency

Answer 40

Galactose can be produced from a glucose metabolite by EPIMERIZATION

Question 41

NADPH produced from the HMP shunt is needed in the ff pathways? (5)

Answer 41

1. Reductive reactions for FA and steroid synthesis 2. Reduction of glutathione 3. NO synthesis 4. Respiratory burst 5. CYP 450 reactions

Question 42

Disease, cherry red spot on macula + (+) hepatosplenomegaly?

Answer 42

Nieman Pick - Sphingomyelinase deficiency

Question 43

Disease cherry red spots ; (-) hepatosplenomegaly

Answer 43

Tay sach’s : Hexosaminidase A

Question 44

Enzyme deficient in Gaucher’s ?

Answer 44

Glucocerebrosidase

Question 45

Enzyme deficient in Krabbe’s?

Answer 45

Galactocerebrosidase