Which of the following statement(s) is/are CORRECT?
- DNA is composed of nucleotides.
- Five types of nitrogenous bases occur in DNA.
- Each phosphate is attached to two deoxyribose units in a single strand of DNA.
- The ratio of adenine to guanine is always 1:1 in a double stranded DNA.
The Correct Option is A, C
Solution and Explanation
(A) DNA is structurally composed of nucleotides, which are the basic building units each containing a phosphate group, a sugar molecule (deoxyribose), and a nitrogenous base. This statement is accurate and fundamental to understanding DNA structure.
(B) This statement is incorrect as DNA comprises only four types of nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G
(C) Correct, as the phosphate backbone of DNA links each phosphate group to two different deoxyribose sugars, one on each side, reflecting the structure of the DNA strand.
(D) Incorrect, because the base pairing rules for DNA specify that adenine pairs with thymine, and cytosine pairs with guanine, leading to an A:T and C:G ratio of 1:1 respectively, not A:G.
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