Many proteins are enzymes

What are enzymes?

Tertiary structure proteins which catalyse reactions

Why do the active sites of enzymes have a specific and uniques shape?

Due to specific folding and bonding in the tertiary structure of the protein

What does the specific and unique shape of the enzyme’s active site mean?

The enzyme only attaches to substrates with a complementary shape

What do the enzyme and substrate form?

Enzyme substrate complex

What are the two models of enzyme action?

• Lock and key model

• Induced fit model (the accepted model)

Explain the lock and key model in 4 steps

1. Substrate fits into enzyme active site due to complementary shape (suggests active site is a fixed shape)

2. Due to random collisions the substrate can collide and attach to the enzyme (forming an enzyme-substrate complex)

3. The charged groups within the active site distort the substrate, lowering the activation energy

4. Products are released and the active site is emptied

Explain the Induced Fit model in 4 steps

1. Enzyme active site slightly changes shape to mould around the substrate

2. Enzyme substrate complex occurs

3. Due to the enzyme moulding around the substrate it puts a strain on bonds, lowering the activation energy

4. Products are removed and the enzyme active site returns to its original shape

What are the 5 factors affecting rate of enzyme controlled reactions?

• Temperature

• pH

• Substrate concentration

• Enzyme concentration

• Enzyme inhibitors

How does too low a temperature affect the rate of enzyme-controlled reactions?

• Means there is not enough kinetic energy for successful collisions between enzyme and substrate

• Lowering rate of reaction

How does too high a temperature affect the rate of enzyme-controlled reactions?

• Tertiary bonds break causing enzyme active site to change shape

• Enzyme denatures

• Enzyme substrate complexes cannot form

• Lowering rate of reaction

How does pH affect the rate of enzyme-controlled reactions?

• Too high/low pH

• Interferes with charges in the amino acids in the active site

• Breaks bonds holding tertiary structure in place

• Active site changes shape

• Enzyme denatures and fewer enzyme-substrate complexes form

How does substrate concentration affect the rate of enzyme-controlled reactions?

• Insufficient substrate

• Fewer collisions between enzyme and substrate

• Slower reaction

How does enzyme concentration affect the rate of enzyme-controlled reactions?

• Insufficient enzymes

• Enzyme active sites become saturated with substrate

• Unable to work faster

What are the two types of enzyme inhibitors?

• Competitive inhibitors

• Non-competitive inhibitors

How do competitive inhibitors affect the rate of enzyme-controlled reactions?

• Competitive inhibitors are similar in shape to the substrate

• Can bind to the active site of the enzyme

• Prevents substrate and enzyme forming an enzyme substrate complex

• So reaction can’t occur

• If more substrate is added it will out compete the inhibitor knocking them out of the active site

How do non-competitive inhibitors affect the rate of enzyme-controlled reactions?

• Non-competitive inhibitors bind to the enzyme away from active site (the allostertic site)

• Causing active site to change shape

• So substrate is no longer complementary in shape to active site

• Enzyme substrate complex can no longer bind

• Adding substrate will not out-compete non competitive inhibitor