This set of Structural Biology Multiple Choice Questions & Answers (MCQs) focuses on “Insulin”.
1. Insulin is a polysaccharide.
a) True
b) False
View Answer
Explanation: Insulin is a polypeptide, made up of 51 amino acids which promotes the storage of nutrients. It has two polypeptide chains – A and B that have 21 and 30 amino acid residues respectively.
2. Which of the following hormones are anabolic with respect to their function?
a) Insulin
b) Glucagon
c) Calcitonin
d) Amylin
View Answer
Explanation: Insulin regulates the metabolism of carbohydrates, fats and proteins by absorbing excess of these biomolecules from blood into liver, skeletal muscle and fat cells. The biomolecules, smaller in size, on absorption are converted into larger molecules like glycogen or fats in the cells, hence is an anabolic hormone.
3. Which of these is a transcription factor for insulin regulation?
a) Polymerase II
b) NFATC1
c) PDX1
d) HDAC1
View Answer
Explanation: Increase in blood glucose levels causes PDX1 to undergo phosphorylation and translocation. It is found to supress glucagon levels and cause histone modifications by methylation, acetylation and deacetylation.
4. Which of the following is the active form of insulin?
a) Monomer
b) Hexamer
c) Dimer
d) Trimer
View Answer
Explanation: Though insulin exists as a hexamer, it is more active in its monomeric state because in monomeric and dimeric states insulin is readily diffusible into blood, while hexamer cannot diffuse as easily. Insulin does not have a trimeric form.
5. Insulin is first synthesized as __________
a) Proinsulin
b) Preproinsulin
c) Preinsulin
d) Pheroinsulin
View Answer
Explanation: Insulin is first synthesized in beta cells as preproinsulin, a single polypeptide chain composed of 24 peptide residues. It is an inactive precursor, which is converted into proinsulin by removal of signal peptide from the N terminal. Proinsulin is then converted to active insulin.
6. In how many phases is insulin released?
a) Single phase
b) Two phases
c) Dependent on glucose levels
d) More than two phases
View Answer
Explanation: Release of insulin by beta cells takes place in two phases. In the first phase, the release is triggered as an immediate response to a sudden rise in blood glucose levels and is short lived. During the second phase(longer period), insulin is released slowly that peaks every 2-3 hours.
7. The receptor to which insulin binds is a _____
a) Homodimer
b) Heterodimer
c) Homotrimer
d) Heterotrimer
View Answer
Explanation: The receptor has an alpha and a beta subunit that form a homodimer. Insulin attaches to the alpha subunit that is exposed to the extracellular surface of the cell while the beta subunits are responsible for phosphorylation of proteins that mediate the effects of insulin.
8. Which of the following is not an effect of insulin?
a) Increased fat synthesis
b) Increased glycogenolysis
c) Increased amino acid intake
d) Decreased glycogenolysis
View Answer
Explanation: Insulin stores glucose and amino acids from blood into fat cells, liver cells and skeletal muscle cells. It also induces breakdown of glycogen into glucose to maintain the blood glucose level. Glycogenolysis is the breakdown of glycogen to increase blood glucose levels.
9. The two primary sites for insulin degradation or clearance are _____
a) Liver and pancreas
b) Pancreas and kidney
c) Pancreas and gall bladder
d) Gall bladder and liver
View Answer
Explanation: After an insulin molecule has served its purpose, it is either removed via systemic circulation by pancreas, or in a single path by liver. Degradation takes place by endocytosis of the complex and then targeted by insulin-degrading enzyme.
10. The two chains of insulin are linked together by one disulphide bond.
a) True
b) False
View Answer
Explanation: The A and B chains of insulin are held by two disulphide bonds with an additional disulphide bond present in the A chain. In this case the bonds have an inter-protein function as they hold two different polypeptide chains in insulin. The three bonds stabilize the structure of insulin.
11. Co-factor aiding the conversion of insulin dimer to hexamer is _____
a) Ca ions
b) Mg ions
c) Zn ions
d) Fe ions
View Answer
Explanation: Though the active form of insulin is its monomeric form, it is more stable in the hexameric conformation which shields or protects the highly reactive insulin. Zn aides in getting excess insulin back to its inactive form, thus balancing the blood sugar level.
12. Insulin cannot be orally administered.
a) True
b) False
View Answer
Explanation: If orally administered, insulin gets broken down into smaller and simpler structures due to reactions taking place in the gastrointestinal tract, which destroys its functionality. Insulin is directly introduced into the blood stream by injections so that it serves its purpose fully by directly absorbing the excess blood glucose, amino acid, etc.
Sanfoundry Global Education & Learning Series – Structural Biology.
To practice all areas of Structural Biology, here is complete set of Multiple Choice Questions and Answers.
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