Answer the following questions concerning a section of doubl

Answer the following questions concerning a section of double-stranded DNA containing 1000 base pairs. a. If the DNA contains 28% adenosine residues, how many guanosine residues are in the DNA? b. Are the nucleotide compositions of each of the two individual strands of DNA identical? Explain. c. If the DNA is entirely in the B-DNA conformation: i. What is the length of the DNA? ii. How many helical turns does the DNA contain? d. If the DNA exists as chromatin, how many nucleosomes should be formed in that section of DNA?

Solution

a. A bind to T & G bind to C. So A is equal to T and G is equal to C. If A is 28%, then T also 28%. Total 56%. The rest 44% are G & C. Only G is 22%. I.e 220.

b. No. The base pairing is Complimentary in nature. So the sequence of the two strands are not Identical

c. 1. In B - DNA the helix length is 34 Angstrom units or 3.4 nm. Each helix contain 10.4 bp. So each base pair length is 3.4 nm / 10.4 = 0.32 nm. Total 1000 bp present, then the length of DNA is 0.32 nm x 1000 = 320 nm

2. 1000 / 10.4 = 96.15 helises (Nearly 100 helices).

d. Each nucleosome contain 200 bp. So from the given DNA, 5 nucleosomes formed (1000/200)