Chapter 12 ( Glycolysis And Pyruvate Dehydrogenases )

Question 1

Glucose sensor for insulin release in Beta-cells of pancreas ?

Answer 1

GLUT2 along with Glucokinase

Question 2

Stimulators of GLUT4 translocation in skeletal muscles ?

Answer 2

Insulin

Exercise by 5’AMP-activated kinase

Question 3

Why does adipose tissue require glucose ?

Answer 3

To form DHAB which is converted to Glycerol phosphate used to store incoming fatty acids as Triglyceride

Question 4

Phases of insulin secretion by pancreatic Beta-cells ?

Answer 4

Phase 1 : within 15 mins , glucose stimulates the release of preformed insulin
Phase 2 : within several hours , glucose stimulates insulin synthesis at the gene level

Question 5

Activators and inhibitors of PFK-1 ?

Answer 5

Activators : 
AMP
Fructose 2,6 bisphosphate 
Inhibitors :
ATP
Citrate

Question 6

Arsenate mechanism ?

Answer 6

Inhibits the conversion o Glyceraldehyde 3-phosphate to 1,3 bisphosphoglycerate by mimicking phosphate
The arsenate containing product is water-labile enabling glycolysis to proceed but with no ATP production

Question 7

What does mutations of glucokinase do ?

Answer 7

Alter the Km for glucose
Mutation that decrease Km result in hyperinsulinemia and hypoglycemia
Mutations that increase Km result in some cases of MODY

Question 8

C-peptide ?

Answer 8

Short polypeptide connecting A-chain to B-chain in the proinsulin , removed after proinsulin is packaged into vesicles in the golgi apparatus

Question 9

Enzymes that catalyzes irreversible reactions in glycolysis ?

Answer 9

Glucokinase / Hexokinase
PFK-1
Pyruvate kinase

Question 10

Pyruvate kinase deficiency characteristics ?

Answer 10

Chronic hemolysis
Increase 2,3BPG which lower HbA affinity to oxygen
Absence of Heinz bodies ( which present in G6PD deficiency

Question 11

Galactosemia caused by deficiency of which enzymes ? And symptoms ? Screening test in newborns ?

Answer 11

Galactokinase and galactose 1-phosphate uridyltransferase
Symptoms :
Catarct in early life
Vomiting and diarrhea following lactose ingestion
Mental retardation and lethargy
Liver damage and hyperbilirubinemia
Screening test : heal prick test

Question 12

Mechanism of cataract in galactosemia ?

Answer 12

Transformation of galactose into galactitol by aldose reductase which accumulate in the lens and causes osmotic damage

Question 13

Why there is no cataract in fructosuria patients ?

Answer 13

Because a fructose is a ketose not an aldose ( doesn’t have aldehyde group for the aldose reductase to work on )

Question 14

Hereditary fructose intolerance defect and symptoms?

Answer 14

Aldolase B deficiency 
Symptoms : 
Lethargy and vomiting 
Liver damage , hyperbilirubinemia , hypoglycemia
Hyperuricemia , lactic acidosis 
Fanconi syndrome

Question 15

Coenzymes used by pyruvate dehydrogenase ?

Answer 15

Thiamine pyrophosphate 
Lipoic acid 
Coenzyme A
FAD(H2)
NAD(H)

Question 16

Enzymes responsible for substrate level phosphorylation in glycolysis ?

Answer 16

Phosphoglycerate kinase

Pyruvate kinase

Question 17

Pyruvate kinase activator ?

Answer 17

Fructose 1,6-bisphosphate ( feed forward activation )

Question 18

Lactate dehydrogenase function ?

Answer 18

Used only in anaerobic glycolysis , reoxidizes NADH to NAD , replenishing the oxidized coenzyme for glyceraldehyde 3aphosphate dehydrogenase so that glycolysis can continuo

Question 19

Diagnostic test of lactose intolerance ?

Answer 19

Positive hydrogen breath test after an oral lactose load

Question 20

Pyruvate dehydrogenase inhibitors and activators ?

Answer 20

Inhibitors : 
Acetyl-CoA
NADH
ATP
Activators : 
Calcium