1) Apparently the fluidity of membranes is important to their biological functions. It was shown that in E. coli the ratio of saturated to unsaturated fatty acids decreases as the temperature decreases. How does the presence of unsaturated fatty acids affect the fluidity of membranes? What role does cholesterol play in mammalian membrane fluidity?

2)A number of factors influence the behavior of a linear, double-strand DNA molecule in a 0.25 M sodium chloride solution. Considering this, explain each of the following observations.
a)The Tm increases in proportion to length of the molecule.
b)As the concentration of sodium chloride decreases the T., decreases.
c)Renaturation of single strands to form double strands occurs more vapidly when the DNA concentration is increased.
d)The T., value is reduced when urea is added to the solution.

3-The ability of bacteria, yeast, and fungi to convert aliphatic hydrocarbons tocarbon dioxide and water has been studied intensively over the past decade because of concerns about the effects of crude oil spills on the environment. Microorganism cannot survive when they are placed in high concentrations of crude oil or any of its components. However, they can utilize hydrocarbons very efficiently when they are placed in a medium in which an extensive lipid-water interface is created by agitation and aeration. Why?

4-Bacterial mutants that are unable to synthesize fatty acids will incorporate them into their membranes when fatty acids are supplied in their growth medium. Suppose that each of two cultures contains a mixture of several types of straight- chain fatty acids , some saturated and some unsaturated, rangingin chain length from 10-20carbon atoms. If one culture is maintained at 18 Cand the other is maintained at 40 oC over several generation , what differences in the composition of the cell membranes of the two cultures would you expect to observe?