3.5: Factors influencing enzyme activity (1)

What are the two main factors affecting enzyme activity in this section?

• Substrate concentration

• Temperature

How does increasing substrate concentration affect enzyme activity?

Rate increases as more substrate molecules are available → more collisions with enzymes.

Why does increasing substrate concentration increase rate?

More substrate molecules → higher chance of successful collisions → more enzyme-substrate complexes.

What happens to rate at very high substrate concentration?

Rate becomes constant (plateaus).

Why does the rate plateau at high substrate concentration?

All enzyme active sites are occupied (enzymes are saturated).

What is meant by a limiting factor?

A factor that restricts the rate of a reaction.

Why are enzymes described as globular proteins?

Because they are folded into a compact, spherical shape, forming a specific tertiary structure.
→ This shape creates the active site.

What is enzyme specificity?

The ability of an enzyme to only bind to a specific substrate and catalyse a specific reaction.
→ Due to the complementary shape of the active site.

What is the lock and key model?

A model where the substrate fits exactly into the active site, like a key into a lock.
→ Emphasises high specificity.

What is the induced fit model?

A model where the active site changes shape slightly to fit the substrate more closely during binding.
→ Gives a better fit and increases reaction efficiency.

What is an enzyme-substrate complex?

A temporary complex formed when a substrate binds to the enzyme’s active site.
→ This is where the reaction takes place.

How do enzymes catalyse reactions?

• Bring substrates close together

• Orient them correctly

• Put bonds under strain
  → This lowers activation energy and speeds up the reaction.

Give examples of enzyme-catalysed breakdown reactions (catabolic).

• Amylase: starch → maltose

• Protease: protein → amino acids

• Lipase: lipids → fatty acids + glycerol

Give examples of enzyme-catalysed synthesis reactions (anabolic).

• Formation of starch from glucose

• Formation of proteins from amino acids
  → Involves condensation reactions (water removed)

Why are enzymes essential for life?

Because without them:

• Reactions would be too slow

• Not enough energy would be available
  → Life processes could not occur fast enough to sustain life