Biological Molecules: Enzymes

Question 1

Metabolism

Answer 1

The sum of all the reactions in a cell or the body. The rate (speed) of chemical reactions is very important. They must happen quickly enough to keep us alive

Question 2

Induced Fit Theorem

Answer 2

• This is when the active site slightly changes shape to mold around the substrate. This puts strain on the bonds and therefore lowers the activation energy
• The enzyme is like a glove and the substrate is like your hand
• The induced fit model is the accepted model for enzyme function

Question 3

Enzymes

Answer 3

• Biological catalysts
• Enzymes are proteins: this means they have a specific 3D shape due to their tertiary structure
• Enzymes are highly specific: each metabolic reaction has its own enzyme to catalyse it

Question 4

Key features of competitive inhibitors

Answer 4

• Similar shape (tertiary structure) to the substrate
• Competes with the substrate for the active site
• Forms an enzyme-inhibitor complex
• Prevents enzyme-substrate complexes being formed
• Slows the rate of reaction

Question 5

Key features of non-competitive inhibitors

Answer 5

• Different in shape to the substrate
• Binds to the allosteric site (not the active site)
• As it binds it causes a conformational change in the tertiary structure of the enzyme including the active site
• Substrate can no longer bind to the active site so no ES complex forms
• Reaction rate slows

Question 6

What is the active site? How is it formed?

Answer 6

The active site is specific and unique in shape due to the specific folding and bonding in the tertiary structure of the protein. This ensures the active site of the enzyme is complementary to one specific substrate

Question 7

What is the ‘activation energy?’

Answer 7

The amount of energy needed to make a reaction happen (break bonds before new bonds can be formed.) Enzymes lower the activation energy by bending and weakening bonds and splitting the reaction into smaller steps

Question 8

What is the Lock and Key method?

Answer 8

Substrate enters active site on enzyme (collision with enough energy and correct orientation) —> An ES (enzyme - substrate) complex forms while the reaction occurs. The enzyme lowers activation energy by bending and weakening bonds in substrate —> Products no longer fit the active site and leaves the enzyme. The enzyme remains unchanged and ready for another substrate.

The active site of the enzyme is exactly complementary to the substrate.

This is no longer the accepted model of enzyme action (induced fit theorem.)