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Thursday, 13 October 2016

Biochemistry-Model question paper for MBBS



1(a) Explain the consequence and role of compartmentation of enzymes. (06 Marks)
(b) Write the open chain structures for (a) D-gluconic acid and (b) D-glucoronic acid. (06 Marks)
(c) There are two possible chair conformers of beta-D-glucopyranose. How many boat conformers are possible? (04 Marks)
(d) The specific rotation of maltose in water is +138 degrees. What would be the concentration of a maltose solution that had an optical rotation of +23 degrees if a polarimeter tube 10 cm long was used? (04 Marks)
2(a) Calculate the isoelectric point of (a) arginine and (b) histidine. (06 Marks)
(b) What are the reasons for the marked stability of an alpha helix? (06 Marks)
(c) What is meant by the statement that a particular conformation of an amino acid residue lies in an unfavourable region of the Ramachandran plot? (04 Marks)
(d) Theronine constitutes 1.8% by weight of the amino acid content of insulin. Given that the molecular weight of theronine is 119, what is the minimum molecular weight of Insulin? (04 marks)
3(a) Why is the triple helix of collagen a better structure for providing tensile strength than the alpha helix? (04 Marks)
(b) The identification of the type and subtype of intermediate filament help in the diagnosis and classification of cancer. Explain. (06 Marks)
(c) How many different molecules of triacylglycerol can be made from glycerol and four different fatty acids? (06 Marks)
(d) The pH of the gastric juice is 1. The cells that produce gastric juice have an internal pH of 7. Calculate the ΔG for transport of protons from these cells into the stomach at 37 degree Celsius temperature. Given R = 8.3 J/mol.K. (04 Marks)
4(a) What feature of the amino acid composition of histones enables them to interact strongly with DNA? (04 Marks)
(b) Why does messenger RNA have the most heterogeneous base sequences of the major forms of RNA present in the cytoplasm of a cell? (04 Marks)
(c) What is the basic difference between the reaction catalyzed by (a) a mutase enzyme and that catalyzed by an isomerase; (b) an oxidase, an oxygenase, and the reverse reaction of a reductase? Give examples. (08 Marks)
(d) Give some examples of enzymes that are smaller than their substrates. (04 Marks)
5(a) How does varying the substrate concentration relative to the enzyme concentration affect the validity of the steady-state assumption and the applicability of the Michaelis-Menten expression? (06 Marks)
(b) Prove that the sum of the control strengths of all enzymes in a linear sequence of reaction is 1. (06 marks)
(c) Write a brief note on the role of ATP in bioenergetics. (04 Marks)
(d) Calculate the mean activity coefficient in a solution of 0.25 mol L-1Na3PO4. (04 Marks)
6(a) How is the concentration of the glucose in the blood maintained (a) during rest after a carbohydrate–rich meal and (b) during prolonged exercise? (04 marks)
(b) Termites exist almost entirely on a diet of cellulose. How is the cellulose degraded by the termites to carbohydrates, which can be used as an energy source. (06 Marks)
(c) If a protein inhibitor of succinyl-CoA synthetase is applied to liver cells and germinating plant cells, what effect would this have on energy production and the synthesis of carbohydrate in both types of cell? (06 Marks)
(d) Calculate the number of molecules of ATP that can be produced by substrate-level phosphorylation of ADP from two molecules of acetyl-CoA in the (a) citric acid cycle and (b) glyoxylate cycle. (04 Marks)
7(a) What effect would a deficiency of carnitine palmitoytransferase in skeletal muscle have on the ability of a person to perform prolonged exercise? (06 Marks)
(b) Why does feeding compounds that act as methyl-group donors to patients with fatty liver alleviate the condition?  (04 Marks)
(c) How is it possible to distinguish between the different cytochromes in the electron-transport chain? (06 Marks)
(d) Given that the internal pH of a mitochondrion is 7.8, and assuming that a mitochondrion has a volume the same as the sphere of diameter 1.4×10-6 m, calculate the number of protons inside the mitochondrion. (04 Marks)
8(a) Glutamine from the diet and from muscle during fasting can be converted into alanine in the intestine. Which enzymes are involved in this conversion? (04 Marks)
(b) What feature of circular, double-helical DNA is essential for it to function as a vector for DNA cloning? (04 Marks)
(c) Decode the following RNA sequence into the corresponding amino acid sequence:
CAU AUU ACU CAU GAA CGU GAA (06 Marks)
(d) What is the difference between a repressor and a corepressor in relation to transcription? (06 Marks)

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