Enzymes as globular proteins and the active site

Overview

Term active site, term biological catalyst and temporary structure formed when substrate binds to an enzyme.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   To which class of protein do enzymes belong?

   Model answer

   Enzymes are globular proteins.

2. 2

   Give two structural features of a globular protein that suit it to acting as an enzyme.

   Model answer

   It is compact with a precise three-dimensional shape, and its hydrophilic groups face outwards so it dissolves in the aqueous cytoplasm.

3. 3

   Define the term active site.

   Model answer

   The active site is a small region on the surface of an enzyme with a shape complementary to that of its substrate, to which the substrate binds.

4. 4

   Which level of protein structure creates the shape of the active site?

   Model answer

   The tertiary structure creates the active site, because folding brings particular R groups together on the surface.

5. 5

   What fraction of an enzyme molecule does the active site occupy?

   Model answer

   The active site occupies only a very small part of the molecule, typically a few amino acid residues out of hundreds.

6. 6

   Explain the role of the amino acids that lie outside the active site.

   Model answer

   They hold the chain in the folded shape that positions the active site residues correctly, so a change anywhere in the chain can alter the site.

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