t_1/2 of an irreversible first-order reaction, S → P is 1 hour. the time (in hours) required to reach 75% completion is

• 1.5

• 2.0

• 2.5

• 3.0

The amino acid alanine has a high propensity to occur in a helical conformation. The circular dichroism spectrum of an equimolar mixture of two 20-residue peptides, one composed of only L-alanine and the other only D-alanine is recorder in the region of 185-250 nm. Which one of the following will be observed?

• No signal: as the chiroptical properties of the two peptides will cancel out

• bands with only negative ellipticity: as helix formed by the D-Ala peptide will be unstable

• Bands with only positive ellipticity: as both the peptides will form right-handed helices

• Bands with identical negative and positive ellipticity

The following small peptide substrates are used for determining elastase activity and the following data have been recorder

Substrate	KM (mM)	kcat (s-1)
P A P A ↓ G	4.02	26
P A P A ↓ A	1.51	37
P A P A ↓ F	0.64	18

The arrow indicates the cleavage site. From the above observations, it appears that:

(A) P A P A F is digested most rapidly.

(B) P A P A G is digested most rapidly.

(C) A hydrophobic residue at the C-terminus seems to be favored.

(D) A smaller residue at the C-terminus seems to be favored.

(E) Elastase always required a smaller residue at the N-terminus of the cleavage site.

Which of the following is true?

• (A), (C) and (E)

• (B), (D) and (E)

• (E) only

• (D), (E) only

The apparent pH of a fluid is 7.45, where bicarbonate buffer is involved for maintaining its pH. Values of pKa of carbonic acid are 6.15 and 10.45. The molar ratio of [conjugate base] : [acid] is

• 1 : 20

• 20 : 1

• 1 : 1000

• 1000 : 1

In order to determine the primary structure of an octapeptide, amino acid composition was determined by acid hydrolysis (A). The intact oligopeptide was treated with carboxypeptidase (B), chymotrypsin (C), trypsin, and CNBr (E). The peptides were separated in each case and acid hydrolysis was carried out for B - E. The Following results were obtained (the brackets represent mixtures of amino acids in each fragment):

(A) (2Ala, Arg, Lys, Met, Phe, 2Ser)

(B) (Ala, Arg, Lys, Met, Phe, 2Ser) and Ala

(C) (Ala, Arg, Phe, Ser), (Ala, Lys, Met, Ser)

(D) (Ala, Arg), (Lys, Phe, Ser), (Ala, Met, Ser)

(E) (Ala, Arg, Lys, Met, Phe, Ser), (Ala, Ser)

Which one is the correct sequence of the oligopeptide?

• Arg-Ala-Ser-Lys-Met-Phe-Ser-Ala

• Arg-Ala-Ser-Lys-Phe-Met-Ser-Al

• Ala-Arg-Ser-Phe-Lys-Met-Ser-Ala

• Ala-Arg-Phe-Ser-Lys-Met-Ser-Ala

Which one of the following pairs of precursors amino acid and alkaloid is correct?

• 'Ornithine aspartate-nicotine' and trptophan -quinone'

• 'Ornithine-nicotine' and 'tyrosine-orphine' 

• 'Tyrosine-quinone' and 'tryptophan-orphine'

• 'Ornithine-quinine' and 'ornithine-aspartate-nicotine'

Poly-L-lysine exits in pure α-helix, β-sheet and random coiled conformations depending upon the solvent conditions. The values of mean residue ellipticity at 220 nm ([θ]₂₂₀) are -35,700, -13,800 and +3,900 deg cm² dmol^-1 for α-helix, β-sheet and random coil conformations of this polypeptide, respectively. The polypeptide exists in α-helix conformation at pH 10.8 and 25°C. Addition of urea leads to a two state transition between α-helix and random coil conformation. It has been observed that [θ]₂₂₂ of the polypeptide is -14800 deg cm²dmol^-1 in the presence of 6M urea. The percentage of the polypeptide in α-helix conformation is:

• 37

• 41

• 47

• 50

The interaction energy between atom A and B is ˜400 kJ mol^-1. The type of interaction between them is

• pi-pi

• covalent

• ion-dipole

• hydrogen bond

Which one of the following bases has the largest hydrogen bonding possibility?

• Adenine

• Guanine

• Cytosine

• Uracil

Enzymes help to lower the activation, energies of reactions by

• covalent interaction with substrates

• binding only with the solvent molecules

• changing reaction equilibria

• forming weak interactions with substrates.