Which of the following is the correct decreasing order for the rate of decomposition of litter constituents?

• Hemicellulose, cellulose, lignin, phenol

• Cellulose, hemicellulose, phenol, lignin

• Hemicellulose, cellulose, phenol, lignin

• Lignin, phenol, hemicellulose, cellulose

The following is the amino acid sequence of a part of a protein encoded by gene 'X'

...Phe Leu Val Pro Ser Tyr Cys...

A mutant for gene 'X' is isolated following treatment with a mutagen. The amino acid sequence of the same region encoded by the mutant gene is as follows:

....Phe Leu Phe Arg Arg Ile....

Which of the following mutagens is most likely to have been used?

• 5-bromouracil

• 2-amino-purine

• Ethyl methanesulfonate

• Acridine orange

In order to precipitate a particular protein by its specific antiserum, it was found that the protein formed cross-linked lattice with specific polyclonal antiserum but failed to precipitate with specific monoclonal antiserum. Which of the following would accurately justify the reason for this behavior?

• The protein has multiple copies of the same epitope specific for the monoclonal antibody.

• The protein has multiple distinct epitopes but each has a single copy.

• There is total absence of epitopes in the protein.

• The protein has multiple copies of different epitopes.

Enzyme parameters of four isozymes is given below:

Isozyme	Km micromolar	Vmax
A	0.1	15
B	1.5	45
C	4.0	100
D	0.01	10

These isozymes are localized in different tissues. In liver the substrate concentration is 0.2 micromolar.

The liver isozyme is likely to be

• A 

• B

• C

• D

Binding of two ligands to their binding proteins was investigated. Following binding isotherms were obtained.

Which of the following statements is correct?

• A is obtained with an oligomeric protein and B is obtained with a monomeric protein.

• B is obtained with protein with positive cooperativity.

• A and B were obtained by the same protein at two different temperatures.

• The profile B is not possible.

Two homologous proteins were isolated from a psychrophile (P) and a thermophile (T). The purified proteins were subjected to denaturation, protease digestion and circular dichroism (CD). Following observations were made :

A. The CD spectra of P and T proteins are identical.

B. Their amino acid composition is 95% identical.

C. T and P are equally susceptible to proteolysis in the presence or absenceof reducing agent.

D. T has higher midpoint of thermal denaturation than P.

The reason for enhanced stability in T is due to

• Altered secondary structure

• Increased number of disulfides in T.

• Increase in water of hydration.

• Increase in number of salt bridges

Acetyl-(Ala)₁₈-CONH₂ exists in α-helical conformation in solution. Most of the backbone dihedral angles (Φ, ψ) will be

• -60°, -30°

• 60°, 30°

• -60°, -30°(50%) and 60°, 30° (50%)

• -80°, 120°

The lifetime of a peptide bond in proteins is very large (∼1000 years). Which statement below is INCORRECT with respect to the stability of the peptide bond?

• The free energy of hydrolysis is negative

• The free energy of hydrolysis is positive and large.

• The energy barrier to be crossed to go to the hydrolyzed state is large.

• The peptide bond can be hydrolyzed by 6N HCl at 100°C.

Two 18-residue helical peptides A and B are enantiomers. They can be distinguished by

• recording their MALDI mass spectrum.

• hydrolysis followed by amino acid analysis.

• sequencing by Edman's method.

• examining their circular dichroism spectra

5-Bromouracil is a base analog that can cause mutation when incorporated into DNA. Which of the following is the most likely change that 5-Bromouracil induces:

• T:A to C:G

• T:A to A:T

• G:C to T:A

• C:G to A:T