A DNA molecule with a relative molecular weight of 120,000 is given, of which 6900 are adenyl nucleotides.

A DNA molecule with a relative molecular weight of 120,000 is given, of which 6900 are adenyl nucleotides. Find the amount of all nucleotides in this DNA. Determine the length of this piece.

Given:
Mr (DNA) = 120,000;
Mr (all A) = 6,900;
Nucleotide Mr = 345,
l nucleotide = 0.34 nm
Find:
n (A), n (T), n (C), n (G),
l (DNA).
Solution.
1. Let’s find the total number of DNA nucleotides.
120,000 / 345 = 348
3. Find n (A)
6,900/345 = 20.
4. According to the principle of complementarity, n (A) = n (T), i.e. n (T) = 20
5. So n (C) = n (G) = 348 – (20 + 20) / 2 = 154
6. Find the length of the DNA. It has two chains, each with 174 nucleotides, which means that the length of the molecule is:
174 * 0.34 = 59.16 nm.
Answer: n (A) = 20, n (T) = 20, n (C) = 154, n (G) = 154, l (DNA) = 59.16 nm.