Question

Calculate the number of weak hydrogen bonds in a DNA strand $204Å$ long with 15% thymine bases.

• A. 154
• B. 162
• C. 138
• D. 120

Answer 1

Answer: (B)

DNA length of one turn is $34Å$ . It means one turn contains 10 base pairs. So $34Å=10$ base pairs.
Hence, $204Å=204\times 10/34=60$ base pairs. As given 15% is thymine $=15/100\times 60=9$ thymine.
Thymine pairs with adenine and hence adenine is also 9. So AT is total of 18. Total $GC=60-18=42$ .
Total hydrogen bonds $=2xAT+3xGC$ (AT shows double bond and GC shows triple bond) $=2\times 18+3\times 42=36+126=162.$