# A fragment of a DNA molecule contains 126 adenyl nucleotides (A), which is 18% of the total number of nucleotides in this fragment.

**A fragment of a DNA molecule contains 126 adenyl nucleotides (A), which is 18% of the total number of nucleotides in this fragment. What is the length of a given DNA fragment and how many cytidyl nucleotides (C) does it contain?**

The total number of nucleotides is 700. Of these, 126 are adenyl, which means 126 thymine. So C and G account for (700- (126 + 126)) / 2 = (700-252) / 2 = 448/2 = 224 cytosines and the same amount of guanine (32% each).

One turn of a double helix of DNA contains 10 pairs of nucleotides and has a length of 3.4 nm. Therefore, one pair of nucleotides occupies a 0.34 nm DNA region. This DNA fragment consists of 2 chains in which 700 nucleotides are contained in total, which means 350 nucleotide pairs. The length of the fragment is 350 * 0.34 = 119 nm.