C3 : Enzyme

define enzyme

A globular protein that acts as a biological catalyst, increasing the rate of chemical reactions without being used up

enzyme–substrate complex

Temporary complex formed when substrate binds to the active site of an enzyme

Define active site

Region of an enzyme whose shape is complementary to the substrate

Explain how enzymes lower activation energy

By forming enzyme–substrate complexes that stabilise the transition state and reduce energy required to break bonds

Describe the lock-and-key hypothesis

Substrate fits exactly into a rigid active site forming an enzyme–substrate complex

Describe the induced-fit hypothesis

Active site changes shape slightly when substrate binds, improving fit and lowering activation energy

How can rate of product formation be measured using catalase

Measure volume of oxygen produced per unit time

How can rate of substrate disappearance be measured using amylase

Measure decrease in starch concentration using iodine test

What is a colorimeter used for

Measuring changes in colour intensity to track reaction progress

What does a colorimeter measure

Absorbance or transmission of light

Effect of increasing temperature on enzyme activity

Increases kinetic energy, collision frequency and enzyme–substrate complex formation

Why enzymes denature at high temperature

Hydrogen and ionic bonds break, altering tertiary structure and active site shape

How pH affects enzyme activity

Changes charge of R groups, disrupting bonds and altering active site shape

Why buffer solutions are used

To maintain constant pH

Effect of increasing enzyme concentration

Increases reaction rate if substrate is in excess

Why rate eventually plateaus

Substrate becomes limiting

Effect of increasing substrate concentration

Increases rate until enzymes are saturated

Define enzyme saturation

All active sites are occupied by substrate

Effect of increasing inhibitor concentration

Decreases rate of enzyme-catalysed reaction

Define Vmax

Maximum rate of reaction when all enzyme active sites are saturated

Define Km

Substrate concentration at which reaction rate is half of Vmax

What does a low Km indicate

High affinity between enzyme and substrate

competitive inhibitor effect on enzyme activity

-Reduces rate by competing with substrate

Effect on Vmax : No change

Effect on Km : Increases Km

non competitive inhibitir effect on enzyme

Alters active site shape

Can it be overcome by substrate :: No

Effect on Vmax :: Decreases Vmax

Effect on Km :: No change

Define immobilised enzyme

Enzyme fixed to an inert support such as alginate

Advantages of immobilised enzymes

• Enzymes can be reused

• Product is not contaminated

• Greater stability to temperature and pH changes

• Suitable for continuous processes

Disadvantages of immobilised enzyme

• Reduced reaction rate

• Diffusion limitations

Why increasing temperature initially increases rate

Increased kinetic energy and collision frequency

Why reaction rate plateaus at high substrate concentration

All active sites are occupied

what does immobilisation does to rate of reaction

does NOT increase reaction rate because substrate diffusion to the enzyme is slower.

Why does the lock-and-key model fail to explain all enzyme behaviour

It assumes a rigid active site and does not account for conformational changes during binding

Explain why enzyme denaturation is irreversible

Bonds maintaining tertiary structure are broken, permanently altering the active site shape

why an enzyme is denatured but its primary structure remains intact

Denaturation breaks hydrogen and ionic bonds but not peptide bonds

which is a better measure of enzyme affinity than Vmax or Km?

Km reflects substrate concentration needed for half-maximal activity, independent of enzyme concentration

Explain why non-competitive inhibitors reduce Vmax

They permanently reduce number of functional enzymes regardless of substrate concentration

Why does immobilisation reduce reaction rate despite enzyme stability

Substrate must diffuse into beads, reducing collision frequency