A6. Enzymes

Question 1

Enzymes as biological catalysts
Enzymes speed up chemical reactions by acting as biological catalysts. They catalyse _____________reactions both at a cellular level (e.g. respiration) and for the organism as a whole (e.g. digestion in mammals). Enzymes can affect structures in an organism (e.g. enzymes are involved in the production of collagen, an important protein in the connective tissues of animals) as well as functions (like respiration). Enzyme action can be _____________-within cells, or ______________- outside cells.

Enzymes are proteins. Enzymes have an active site, which has a _________shape. The active site is the part of the enzyme where the ____________molecules bind to. Enzymes are highly __________due to their _________ ____________

Answer 1

Enzymes as biological catalysts
Enzymes speed up chemical reactions by acting as biological catalysts. They catalyse metabolic reactions both at a cellular level (e.g. respiration) and for the organism as a whole (e.g. digestion in mammals). Enzymes can affect structures in an organism (e.g. enzymes are involved in the production of collagen, an important protein in the connective tissues of animals) as well as functions (like respiration). Enzyme action can be intracellular-within cells, or extracellular - outside cells.
Enzymes are proteins. Enzymes have an active site, which has a specific shape. The active site is the part of the enzyme where the substrate molecules bind to. Enzymes are highly specific due to their tertiary structure

Question 2

How enzymes speed up reactions
Enzymes lower the amount of activation energy that’s needed, often making reactions happen at a _______ _____________than they could without an enzyme. This speeds up the _____ of __________.

Answer 2

Enzymes lower the amount of activation energy that’s needed, often making reactions happen at a lower temperature than they could without an enzyme. This speeds up the rate of reaction.

Question 3

When a substrate fits into the enzyme’s active site it forms an enzyme-substrate complex-it’s this that lowers the activation energy.
Here are two reasons why:

Answer 3

• If two substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily.
• If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily.

Question 4

The ‘lock and key’ model (1 thing)

Answer 4

• the substrate fits into the enzyme in the same way that a key fits into a lock-the active site and the substrate have a complementary shape.

Question 5

Induced Fit Model (4 steps)

Answer 5

• Substrate approaches active site and is not complementary at first
• Enzyme moulds to substrate
• Change in tertiary structure puts a strain on bonds of substrate, lowering activation energy.
• ES complex is formed

Question 6

Enzyme properties (4 points)

Answer 6

• The active site’s shape is determined by the enzyme’s tertiary structure
• Enzymes are very specific
• only one complementary substrate will fit into the active site.
• The primary structure (amino acid sequence) of a protein is determined by a gene. If a mutation occurs in that gene, it could change the tertiary structure of the enzyme produced meaning not complementary and no E-S complex formed