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

What constitutes the structure of proteins?

1. Carbohydrate chains

2. Amino acids

3. Fatty acid chains

4. Nucleotide sequences

The correct answer is: Amino acids

The structure of proteins is fundamentally made up of amino acids, which are organic molecules characterized by a central carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a distinctive side chain (often referred to as the R group). These amino acids link together through peptide bonds to form polypeptide chains, which then fold into specific three-dimensional shapes that determine the protein's function. The sequence and arrangement of amino acids in a protein are crucial because they dictate how the protein will fold and what role it will play in biological processes. Variations in this sequence can lead to changes in structure and, consequently, in function, highlighting the importance of amino acids as the building blocks of proteins. Other choices do not contribute to the structure of proteins: carbohydrate chains are associated with polysaccharides; fatty acid chains are components of lipids; and nucleotide sequences form the basis of nucleic acids like DNA and RNA. Thus, the correct answer identifies the essential role of amino acids in constructing proteins.