Chapter 12, Problem 3A

Summary Introduction

Introduction :

DNA is a nucleic acid which is made of pentose sugar, nitrogenous bases and a phosphate molecules. The pentose sugar or five-carbon sugar is deoxyribose and the nitrogenous bases are adenine, guanine, cytosine and thiamine.

Answer to Problem 3A

Correct answer :

The correct answer is option (C) nucleotides.

Explanation of Solution

Explanation/justification for the correct answer :

Option (C) nucleotides. Nucleotides are the building blocks that make up DNA. Nucleotides are the subunits of nucleic acids (DNA and RNA) which consist of a five-carbon sugar, a phosphategroup, and a nitrogenous base.Thus, the correct answer.

The explanation for the incorrect answer :

Option (A) ribose. It a five-carbon or pentose sugar which is present in the RNA not DNA. Thus, this is an incorrect option.

Option (B) purines.Purines are nitrogenous bases which alone cannot make DNA. Thus, this is an incorrect answer.

Option (D) phosphates. Phosphates are only the part of nucleotides. Phosphates alone cannot be the building block of the DNA. Thus, this is an incorrect answer.