Chap 3: Enzymes

Q: What are enzymes and their key features?

A: Enzymes are globular proteins that catalyse metabolic reactions. They are biological catalysts

Q: How do intracellular and extracellular enzymes differ

A:Intracellular: made and used inside the cell. Extracellular: made in the cell but secreted to function outside.

Q: What does the lock-and-key model state?

A: The active site has a specific shape into which the substrate fits exactly.

Q: What does the induced fit model explain?

A: The substrate is partially complementary; the active site alters shape slightly for a better fit

Q: How do enzymes reduce activation energy?

A: By positioning substrates so bonds break more easily or by altering shape (induced fit) to facilitate conversion to products.

Q: Why is the enzyme reaction rate highest at the beginning?

A: Substrate concentration is high

Q: How does temperature affect enzyme activity?

A:Low temperature → slow molecule movement. Increasing temperature → more collisions, faster reactions. Too high → enzyme denatures (H-bonds/ionic bonds break).

Optimum for humans ≈ 40°C.

Q: How does pH change enzyme activity?

• H⁺ ions affect R-groups and ionic bonds

• Break the structure of active sites

Q: What happens as enzyme concentration increases?

A: Reaction rate increases linearly as long as substrate is abundant

Q: How does substrate concentration affect enzyme activity?

A: Rate increases with substrate concentration until Vmax

Q: What is competitive inhibition?

A: A molecule similar to the substrate competes for the active site. Can be reversed by increasing substrate concentration.

Q: What is non-competitive inhibition?

A: Inhibitor binds to an allosteric site

Q: What is end-product inhibition?

A: Final product of a pathway binds to the enzyme elsewhere

Q: What does Km represent?

A: Km is the substrate concentration at half Vmax. Lower Km = higher enzyme affinity for the substrate.

Q: How are enzymes immobilised using alginate beads

A: Enzyme mixed with sodium alginate → droplets added to calcium chloride → beads form

Q: What are advantages of immobilised enzymes?

A: Longer shelf life, Reusable, Easily recovered, Product not contaminated, Reduced product inhibition, Greater stability / less denaturation

Vmax

• max rate of reaction at

  saturating substrate conc

• all of the active sites are occupied

inhibitor affects on the rate of reaction

1. competitive inhi

→ Vmax unchanged

→ Km increase

2. non-competitive inhi

→ Vmax decreases

→ Km unchanged

affinity

enzymes willingness to bind to a substrate

enzymes affinity and Km correlation

Enzymes with lower value of km has a high affinity to its substrate and a higher value of km has a lower affinity.

increase substrate conc can…

• increase rate of reaction when there are competitive inhi

• no change when there are non competitive inhi