Question

12. You have a short piece of DNA. One strand has the following sequence: 5’ AGCTACTCCTAA 3’.

a. Please write down sequence of the other strand, starting with the 5’ end. (0.2 pt)

b. If these two strand wind together as a B form DNA, how long do you expect this DNA to be? (0.2 pt)

c. How many hydrogen bonds are there to stabilize the structure of this DNA? (0.2 pt)

d. Besides hydrogen bonds, what other forces stabilize the structure of this DNA? Why? (0.2 pt)

Answer 1

12). Original strand 5' AGCTACTCCTAA 3'

a) sequence if the other strand starting from 5' end would be 5' TTAGGAGTAGCT 3'

b). In B form of DNA the length of 11 (~10.5) nucleotide base pairs in one helix is 3.4 nm and the distance between two adjacent base pairs is 0.34 nm. As there are 12 base pairs in the given DNA, so its length would be 3.4 + 0.34 = 3.74 nm.

C). A and T form 2 hydrogen bonds in between them whereas G and C form 3 bonds. As there are 7 AT pairs, so they will form 14 hydrogen bonds. There are also 5 GC pairs which will form 15 hydrogen bonds. In total there will be 29 hydrogen bonds.

D). Besides H bonds the structure of the DNA helix is stabilized by van der Waals forces and hydrophobic interactions between the nitrogenous bases and the surrounding sheath of water.