1. In the formation of the secondary structure of a protein, which of the follow

Question

1. In the formation of the secondary structure of a protein, which of the following are most responsible for holding an alpha-helix region in its helical form? (A) lonic bonds (B) Hydrogen bonds (C) Disulfide bonds (D) Hydrophobic interactions (E) van der Waals interactions 2. Separation of molecules according to size can be achieved by which of the following? (A) Gel-filtration chromatography (B) lon-exchange chromatography (C) Affinity chromatography (D) Isoelectric focusing (E) X-ray diffraction 3. Which of the following pathways is most likely taken by newly synthesized histones? (A) Rough endoplasmic reticulum Golgi complex -secretory vesicle (B) Rough endoplasmic reticulum Golgi complex nucleus (C) Rough endoplasmic reticulumsmooth endoplasmic reticulum nucleus (D) Cytoplasm-nucleus (E) Cytoplasm >rough endoplasmic reticulum >Golgi complexnucleus 4. How many different types of gametes could be produced by an individual with the arbitrary genotype of AAbbCCDdEe? (A) Two (B) Four (C) Six (D) Eight (E) More than eight 5. Which of the following best explains how the activity of an enzyme is regulated by an allosteric inhibitor? (A) Direct competition between the binding of the inhibitor and the binding of a substrate to the active site (B) Induction of a conformational change in the enzyme by the inhibitor, which affects enzyme activity (C) Irreversible binding of the inhibitor to the enzyme, which affects enzyme activity (D) Inhibition of the transcription of the gene encoding the enzyme by the inhibitor (E) Denaturation of the protein induced by binding of the inhibitor

Explanation / Answer

1. The alpha-helix in secondary structure of protein is stablized by Hydrogen bonds between amide groups and the carbonyl groups of amino acids. The two amino acids linked by H-bonds are situated 3 amino acids apart. In one turn of alpha-helix, 3.6 amino acids are present.

Option (B) is correct.

2. It can be achieved by gel filtration chromatography. In this technique, porous beads are packed in a column and a mixture of molecules to be separated is passed through it. Small sized molecules enter the beads if their size is smaller than pore size of beads and elute later. Larger molecules are unable to enter the beads and elute first.

Option (A) is correct.

3. Histone proteins are present in nucleus and play an important role in DNA packaging and condensation. DNA being negatively charged is wrapped around positively charged histone proteins. All the proteins that function in nucleus are synthesized in the cytosol and then imported to nucleus through nuclear pores.

Option (D) is correct.

4. The formula to calculate number of gametes possible for a given genotype is 2nwhere n is the number of heterozygous genes.

Here, n = 2 for genes D/d and E/e.

Diff. types of gametes for genotype AAbbCCDdEe = 22 i.e. 4

Option (B) is correct.

5. An allosteric inhibitor is a reversible inhibitor which decreases the affinity of enzyme for substrate by binding at a location other than active site (site where substrate binds). When it binds to the enzyme, it introduces a conformational change in shape of active site so that substrate can no longer bind there.

Option (B) is correct.

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