Question

Why is it reasonable to assume that helix nucleation is a purely entropic event?

Select one:

a. Nucleation is accompanied by a big increase in translational entropy.

b. Nucleation is accompanied by a big decrease in translational entropy.

c. Nucleation is accompanied by a big increase in conformational entropy.

d. Nucleation is accompanied by a big decrease in conformational entropy.

e. Nucleation is accompanied by a big increase in the entropy of the solvent.

f. Nucleation is accompanied bya a big decrease in the entropy of the solvent.

g. Nucleation is accompanied by a big increase in the electrostatic repulsion between the strands.

h. Nucleation creates a stacking interaction.

duplexes have the same standard enthalpy of helix formation, but the formation of duplex X results in a greater standard entropy loss than does the formation of duplex Y.

Which of the following are likely to be correct:

Select one:

a. Duplex X will have a higher melting temperature than duplex Y.

b. Duplex X will have the same melting temperature as duplex Y.

c. Graphs of 1/T_m versus  ln(C_T)for the two duplexes will be parallel.

d. Graphs of 1/T_m versus  ln(C_T)for the two duplexes will converge at low C_T.

e. Graphs of 1/T_m versus  ln(C_T)for the two duplexes will be superimposable.

f. None of the above.

Answer 1

1.The correct answer is option D) Nucleation is accompanied by a big decrease in conformational entropy, because The helix/ coil transition serves as a simple example of a cooperative folding process, commonly described by a nucleation propagation mechanism.The prevalent view is that coil structure must first form a short segment of helix in a localised region despite paying a free energy cost nucleation.Afterward helical structure propagates outward from the nucleation site.Both processes entail enthalpy- entropy compensation that derives from the loss in conformational entropy on helix formation with concomitant gain in favourable interaction.

2. In these question there should be a picture of graph should be present then only I can know, but still according to my knowledge the correct answer would be option c) Graphs of 1/Tm versus ln(CT) for the two duplexes will be parallel because high DNA concentrations favor duplex formation which will increase the Tm.