Question

1. Upon transition of a GC-rich DNA fiber from the B- to the Z-form (e.g. upon adding 3 M NaCl), does the fiber get longer or shorter, and by what percentage?

2. A double-stranded DNA molecule was found to have a total of 10,000 A+T base residues and 14,000 G+C residues. Analysis of one of the strands of the DNA showed that it had 3,000 A and 4,000 C residues. What is the number of T and G base residues on this strand.  

3. How many different triacylglycerols containing both myristate and palmitate [and only these fatty acids] are possible?

Answer 1

1. In B form the distance betwwen two base pair is 3.4 Å while in Z form the distance increase to 3.7 Å. Therefore, the transition from B to Z form increases the fiber length. The length increase percentage will be 12.1

2.Total amount of A+T=10,000 , and we know that A=T, therfore, number of A=10000/2=5000 and number of T=5000.

Similarly, Number of G=Number of C and if the total G=C content is 14,000 then Only G=7000 and only C=7000.

Now as per the question, a single strand has A=3000 so the rest of the A (5000-3000)=2000 is present in another strand. If A=T then, first strand contain 2000 T.

again, a single strand has 4000 C, so rest of the C (7000-4000)=3000 present in the second strand and therefore 3000 G is present in the first strand.

The single strand contain A=3000, T=2000, G= 3000 and C=4000.

3. saturated triglycerides are fond in Myristate and Palmitate