Question

In a $68$nm long DNA molecule, Adenine constitutes $25\%$. How many hydrogen bonds would be present between the strands? (Average length of a nucleotide is $3.4$ Angstroms)

• A. $250$
• B. $350$
• C. $500$
• D. None of these

Answer 1

The correct option is A $250$

As the average length of a nucleotide is 3.4 Angstrom hence there are 200 nucleotides present in 68 nm long DNA. 2 nucleotides form a base pair hence 100 base pairs are present. Adenine-Thymine forms a base pair with a double hydrogen bond and Guanine-Cytosine form base pair with a triple bond.

According to the question, 25% of this DNA molecule consists of Adenine which means that equal percent of Thymine is present as well forming 50% DNA as Adenine-Thymine base pair ( 50 base pairs) While Rest of the 50% DNA consists of Guanine -Cytosine ( 50 base pairs ).

Based on this number of hydrogen bonds present are -

2*50 + 3*50 = 250.

So, the correct option is '250'.