Humber Admissions Practice Test

What is a nucleotide?

1. A basic structural unit of proteins

2. A building block of DNA comprising a sugar, base, and phosphate

3. A type of RNA molecule

4. A complex carbohydrate

The correct answer is: A building block of DNA comprising a sugar, base, and phosphate

A nucleotide serves as the fundamental building block of DNA and is composed of three essential components: a sugar molecule, a nitrogenous base, and a phosphate group. This structure is critical in encoding genetic information and allows for the formation of the DNA double helix. Each nucleotide connects to others through covalent bonds, forming long chains that make up the DNA strand. In DNA, the sugar is specifically deoxyribose, the nitrogenous bases are adenine, thymine, cytosine, and guanine, and the phosphate group links the sugar of one nucleotide to the sugar of the next, creating a backbone for the DNA structure. This tripartite structure is pivotal for processes such as DNA replication and transcription, enabling the precise transfer of genetic information during cell division and protein synthesis. Other options present different biological concepts that do not accurately describe a nucleotide. For instance, although proteins are made up of amino acids, they are not structurally constructed from nucleotides. Similarly, RNA molecules consist of nucleotides, but they are distinct from nucleotides themselves. Complex carbohydrates refer to larger molecules made of sugar units and are also unrelated to the composition of nucleotides.