A double-stranded DNA molecule is 1 cm long, and the percentage of thymine is 22

Question

A double-stranded DNA molecule is 1 cm long, and the percentage of thymine is 22%. a. How long is the DNA in nm? b. How many complete turns are there in the DNA? c. How many guanines would be found in this DNA molecule? How many telomeres are present in a human somatic cell? Which of the following DNA double helices would be more difficult to separate into single-stranded molecules by treatment with heat, which breaks hydrogen bonds? A. 5'­ATACGATTTACGAGA-3' 3'-T ATGCTAA ATGCTCT-5' B. 5'-GGCGTACCAGCGCAT-3' 3'-CCGCATGGTCGCGTA-5'

Explanation / Answer

a) The linear length of 1 b.p is 3.4 angstrom = 3.4 x 10 -10 meter;

1cm = 10 -2

10-2 / 3.4 x 10 -10 = 2.9 x 107 b.p

A= 22 % ; T = 22% ; G = 28% ; C = 28%

b) No of turn = no of b.p x 10

                      2.9 x 107 b.p x 10 = 29 x 107

c) A = 22 % so T = 22% ; G = 28%; C = 28%

7. somatic cell consists of 23 pairs of chromosomes so each chromosomes has two end of telomerase so total 46 x 2 = 92 tolmeres

8. Melting temperature of DNA refer higher GC content due to this we need high energy to breaks hydrogen bonds.

A. GC content is low ie., 5 GC b.p

B: GC content is high i.e., 8 GC b.p so that B sequence more difficult to separate into single stranded molecule

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