LIFE SCIENCE PART C (JUNE 2017) 2017

A serine protease was tested for its activity on the following peptide substrates of different lengths and sequences. The obtained kinetic parameters of the protease are shown along with the peptide.
Arrow denotes site of cleavage. Based on the above data, the following statements are made:
a. Catalytic efficiency (Kcat/Km) increases with the size of the peptide.
b. Amino acid at the hydrolytic cleavage position of the peptide is critical for binding of the peptide with the protease.
c. Catalytic efficiency decreases from three amino acid peptide to four amino acid peptides. Which of the following combinations of the above statements is correct?

A membrane associated protein is composed of seven “α-helices”, with each helix containing 19 hydrophobic residues. While treating the membrane with all kinds of proteases, a major portion of this protein remains intact. Treatment with high salt (till 1.5M NaCI) and buffer with pH 5.0 failed to dissociate this protein from the membrane. Predict the most appropriate nature and orientation of this protein in the membrane.

When the cholera toxin (protein of Mr. 90,000 Da) gains access to the human intestinal tract, it binds tightly to specific receptors in the plasma membrane of the epithelial cells lining the small intestine, causing membrane bound adenylyl cyclase to undergo prolonged activation resulting in extensive loss of H2O and Na+. Pre-treatment of the epithelial cells with various phospholipases and proteases failed to inhibit the binding of cholera toxin to its receptor and the fluid loss but treatment with exoglycosidase, prior to binding, significantly reduces these effects. Which of the following molecules could be the receptor for this toxin?

α-bungarotoxin binds to acetylcholine receptor (AChR) protein with high specificity and prevents the ion- channel opening. This interaction can be exploited to purify AChR from membrane using

In Schizosaccharomyces pombe, the recessive (cdc2r) and dominant (cdc2D) mutants have opposing phenotypes. While cdc2D produces abnormally small cells, cdc2r produces abnormally long cells. Some possible explanations are given below.
(A) cdc2D may lack interaction with WEE1
(B) cdc2r may not interact with CDC13 kinase
(C) cdc2D may not interact with CDC25 phosphatase
(D) cdc2r cells may be deficient in interaction with either CDC25 or WEE1 Which combination of the above statements is correct?

Given below are statements related to protein structures
(A) The dihedral angles of an amino acid X in Acetyl-X-NMethyl amide in the Ramachandran plot, occur in very small but equal areas in the left and right quadrants. It can be concluded that X is not one of the 20-coded amino acids.
(B) The dihedral angles of a 20-residue peptide are represented in the Ramachandran plot. It is possible to conclude that the peptide does not have a proline.
(C) Two proteins can have a similar fold even if they do not share significant similarity in their primary structure.
(D) On denaturation of a protein by urea, the interactions that would be disrupted are ionic bonds and van der Waal's interaction but not disulfide bonds.
Choose the combination with ALL CORRECT answers: