2.1.18 Biology- Enzymes are globular proteins

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All enzymes are protein:

A globular protein has a specific 3D shape of tertiary structure. The shape comes from the proteins primary structure (the specific sequence of amino acids that form the protein) and its secondary structure. In globular proteins, the final 3D shape usually has hydrophobic amino acid R-groups in the centre of the ‘ball’, and hydrophilic amino acid R-groups around the outside of the ball. The amino acid chain spirals, pleats and turns to form the overall structure.

All enzymes are very similar in many ways:

·         they are globular proteins- generally soluble in water

·         they act as catalysts – speeding up chemical reactions, but not being ‘used up’ as part of the reaction

·         they are specific- catalysing a reaction involving only one type of substrate

·         the globular structure contains a ‘pocket’ of cleft area called an active site

·         their activity is affected by temperature and pH


The active site is a tiny part of an enzyme:

Enzymes are relatively large molecules, consisting of hundreds of amino acids. The vast majority of the amino acids are involved in maintaining the specific tertiary structure of the enzyme. Enzymes function, like the function of all proteins, is related to shape. For any enzyme to work properly, the tertiary structure must be maintained in a very specific way.

Essentially, the whole primary, secondary and tertiary structure of enzymes is involved in achieving a very specific shape for the active site. The active site is the area of the enzymes where the catalytic activity


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