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

What are enzymes primarily composed of?

1. Carbohydrates

2. Fats

3. Nucleic acids

4. Proteins

The correct answer is: Proteins

Enzymes are primarily composed of proteins. This is because enzymes are biological catalysts that accelerate chemical reactions in living organisms, and their ability to function effectively relies on their protein structure. The specific sequence of amino acids in a protein determines its shape, and this shape is crucial for the enzyme's activity. The active site of an enzyme, where substrates bind, is formed by the folds and bends of its polypeptide chain. The other options, such as carbohydrates, fats, and nucleic acids, serve different roles within biological systems. Carbohydrates are primarily energy sources and structural components, fats serve as energy reserves and are involved in cell membrane structure, and nucleic acids are essential for genetic information storage and transmission. While these biomolecules are vital for life, they do not perform the catalytic functions that enzymes do, which is why proteins are the correct answer when discussing the primary composition of enzymes.