5 - Enzymes

Question 1

Define catalyst and enzyme

Answer 1

A substance that increases the rate of reaction (2)
and is not changed by the reaction (1)
Enzymes are proteins that are involved in all metabolic reactions (1)
where they function as biological catalysts (1)

Question 2

Describe why enzymes are important in all living organisms

Answer 2

They maintain reaction speeds of metabolic reactions (3)
at a rate that can sustain life (2)

Question 3

Explain enzyme action

Answer 3

Enzymes randomly collide into substrates (1)
Substrate with a complementary shape to active site of enzyme will fit into active site (1)
(OE; substrates without complementary shape will not fit into active site, won’t react, won’t form E-S complex)
so when an enzyme collides with complementary substrate, an enzyme-substrate complex is formed (1)
Substrate reacts and forms products (1)
ref. to specific, reusable/unchanged (1)

Question 4

Explain why the shape of an enzyme is important

Answer 4

Substrate binds with active site of enzyme (1)
only if the substrate is complementary / has a complementary shape to active site (2)
to allow for enzyme-substrate complex to form (1)
Enzymes are specific to one type of substrate due to shape (1)

Question 5

Explain the effects of change in temperature on enzyme activity

Answer 5

Increase in temperature increases the kinetic energy of enzymes/substrates/both (1)
which increases the number of effective collisions between enzymes and substrates (1)
At low temperatures enzymes do not denature but work slower due to less kinetic energy (1)
Enzymes have an optimum temperature that they work at (or ref. to optimal temp. for human enzymes is 37’C) (1)
If temperature is too high enzymes will denature (1)
Active site deforms/loses its shape, substrates no longer fit AND denaturation is irreversible (1)

Question 6

Explain the effects of change in pH on enzyme activity

Answer 6

Enzymes have different optimum pH values depending on their environment (1)
ref. to pepsin/trypsin working in acidic/alkaline environments and having adjusted optimum pH (1)
Increase/decrease in pH from optimum pH gradually deforms active site so substrates no longer fit (2)
There is a gradual decrease in activity (as pH changes) from optimum pH, as some enzymes progressively denature this way (1)