A Level Biology Practice Exam

What determines the primary structure of a protein?

1. The sequence of fatty acids

2. The sequence of monosaccharides

3. The sequence of amino acids

4. The 3D shape of the protein

The correct answer is: The sequence of amino acids

The primary structure of a protein is defined by the specific sequence of amino acids that make up the polypeptide chain. This sequence is determined by the genetic information encoded in an organism's DNA. Each type of protein has a unique amino acid sequence, which directly influences the protein's overall structure and function. While fatty acids and monosaccharides are important building blocks for lipids and carbohydrates respectively, they do not play a role in the primary structure of proteins. The three-dimensional shape of a protein, although crucial for its function, is determined by higher levels of structure (secondary, tertiary, and quaternary) rather than the primary sequence itself. Thus, the sequence of amino acids is the correct determination of a protein's primary structure.