Final answer:
The building block of DNA and RNA is the nucleotide, made up of a phosphate group, a pentose sugar, and a nitrogen-containing base. These nucleotides are fundamental for the structure and function of DNA and RNA. The correct option is b.
Step-by-step explanation:
The structural subunit (building block) of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) is the nucleotide. Nucleotides are composed of three parts: a phosphate group, a pentose sugar, and a nitrogen-containing base.
The four nitrogenous bases found in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T), while RNA contains uracil (U) instead of thymine.
Nucleotides are essential for the primary structure of DNA and RNA. The pentose sugar in DNA is deoxyribose, whereas RNA contains ribose. Nucleotides are linked together to form the long strands of DNA and RNA, which are crucial for genetic encoding and protein synthesis. The correct option is b.