Enzyme explanations

How does an enzyme catalyse a reaction

• The enzyme’s unique tertiary structure means it has an active site complementary to the substrate

• The substrate binds to the enzyme by induced fit - it causes the active site to change shape slightly to become more complementary to the substrate, by disrupting bonds in the tertiary structure of the enzyme

• An enzyme-substrate complex is formed

• The binding of substrate to enzyme stresses bonds within the substrate so they are easier to break - this means that the enzyme has lowered the activation energy of the reaction

Why are enzymes specific to certain substrates

They have unique tertiary structures which give them active sites that are complementary to their specific substrates

Describe the induced fit model

The active site of the enzyme is not exactly complementary to the substrate. When the substrate binds to the enzyme to form an enzyme-substrate complex, the active site changes shape so that it is exactly complementary to the substrate, because the bonding in the tertiary structure of the enzyme has been disrupted.

Enzyme inhibition

Competitive inhibition - the inhibitor is complementary to the active site of the enzyme so can compete with eh substrate for the active site and bind to the enzyme instead of the substrate - this means that fewer enzyme-substrate complexes will form.

Non-competitive inhibition - the inhibitor binds to an allosteric site on the enzyme, disrupting the bonding in the tertiary structure and therefore changing the shape of the active site of the enzyme. This means that it is no longer complementary to the substrate, so fewer enzyme-substrate complexes form.