OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What do nucleotides primarily consist of?

1. Base and amino acid

2. Sugar and phosphate

3. Fatty acids and glycerol

4. Proteins and carbohydrates

The correct answer is: Sugar and phosphate

Nucleotides primarily consist of a sugar, a phosphate group, and a nitrogenous base. The sugar is usually ribose in RNA or deoxyribose in DNA, and the phosphate group helps form the backbone of the nucleic acid structure by linking the sugars together. The nitrogenous base (which can be adenine, thymine, uracil, cytosine, or guanine) is crucial for encoding genetic information and forming base pairs in the structure of DNA and RNA. Options that mention amino acids, fatty acids, or proteins and carbohydrates do not accurately describe nucleotide composition, as they refer to different biological molecules. Amino acids are the building blocks of proteins; fatty acids are components of lipids; and proteins and carbohydrates are distinct macromolecules that serve different functions in the body. Understanding the structure of nucleotides is fundamental, as they play a vital role in genetics and biochemistry.