Question

In a DNA double helix, _____________________.

A) the two DNA strands are identical.

B) purines pair with purines.

C) thymine pairs with cytosine.

D) the two DNA strands run antiparallel.

Both A and D are correct

Both B and C are correct

Answer 1

Answer :

D. 'The two DNA strands run antiparallel' is the correct statement.

Discussion and explanation :

DNA is genetic material which is stored in nucleus of cell in eukaryotes. DNA lies loosely in cytosol in prokaryotes because they lack membrane bound nucleus.

Features of DNA double helix model :

1) DNA helix comprises of two DNA strands which are complementary to each other > Hence strands are complementary but not identical.

2) DNA are polynucleotide chains, sugar and phosphate form the backbone while bases project inside

3) Adenine pairs with thymine with two hydrogen bonds while cytosine pairs with guanine with three hydrogen bonds. Adenine and guanine are purines while thymine and cytosine are pyrimidines > Hence purines pairs with pyrimidine and thymine pairs with adenine.

4) Both DNA strands run antiparallel to each other > This is the correct statement.