Question

Please show all work and answer all parts of the question. Thanks

3. When self-complementary strands of DNA are mixed, they form a double-stranded DNA at low temperatures but dissociate to single strands as the temperature is raised: T(C) A (oligoA-T) This can be observed by an increase in the absorbance of the solutions at 260 nm (The double helix is said to show "hypochromicity" at this wavelength) 10 15 20 25 30 35 40 45 50 0.720 0.732 0.740 0.767 0.801 0.846 0.874 0.891 0.903 1.003 Data for an experiment is given on the right Short complementary DNA strands made of the “A" and "T" nucleotides (oligoA-T) are mixed at different temperatures and the absorption of the solution [A] is measured. a. Assume that the molecules are duplexes (D) at the lowest temperatures for which data are given and single strands (S) at the highest temperatures. Calculate the fraction present as duplex at each temperature b. Plot out the fraction of D as a function of temperature in Excel. Use this to determine the melting temperature of each oligomer (remember, that is the temperature at which the fraction of strands in in the D form and S form are equal)

Answer 1

T_m is the temperature at which the absorbent of UV light is 50% is 50% INA is angle standard For the linear relationship between A_c and T, assume A = mT + C At 55 degree C, 1.003 = m times 55 + C At 5 degree C, 0.711 -m times 5 + C Multiply Eqn 2 by 11 both sides 0.711 times 11 = m times 55 + 11 C Subtracting eqn (1) from (3) -1.003 = m times 55 -C implies 6.818 = 10 C C = 0.6818 and m = 1.003 -0.6818/55 implies A = 0.00584 times T + 0.6818 Proportion of SS DNA at 5 degree C = 0 Preparation of SS DNA at 55 degree C = 50 % y = mT + C 100 = m times 55 + C 0 = m times 5 + C 0 = 55 times m plusminus