A Level Biology Practice Exam

What are peptides?

1. Chains of carbohydrates

2. Chains of nucleotides

3. Chains of amino acids

4. Chains of fatty acids

The correct answer is: Chains of amino acids

Peptides are indeed chains of amino acids, which are the building blocks of proteins. When two or more amino acids link together through peptide bonds, they form a peptide. Peptide bonds are covalent bonds formed during a condensation reaction, where the amino group of one amino acid reacts with the carboxyl group of another, releasing a water molecule in the process. Peptides can vary in length; they can be as short as two amino acids (dipeptides) or consist of many more, forming oligopeptides or polypeptides depending on the number of amino acids involved. The specific sequence of amino acids in a peptide chain determines its structure and function, which is critical for the role of peptides in biological processes, including acting as hormones, neurotransmitters, and as part of larger proteins. In contrast, the other options refer to different types of biological macromolecules: carbohydrates are polysaccharides made of sugar units, nucleotides are the building blocks of nucleic acids like DNA and RNA, and fatty acids are components of lipids. Each of these has distinct structures and functions, separate from the role that peptides play in biochemistry.