Topic 5

Question 1

What is a catalyst?

Answer 1

A substance which increases the rate of reaction without being used up or changed itself

Question 2

What are enzymes?

Answer 2

Enzymes are biological catalysts that
speed up the rate of metabolic reactions

Question 3

Describe the structure of enzymes

Answer 3

Enzymes are proteins that contain a highly specific active site that fits a specific substrate

Question 4

Why are enzymes necessary in biological systems?

Answer 4

They speed up reactions so that less energy is needed for the reaction to occur

Question 5

Describe enzyme action

Answer 5

A substrate that fits the specific active site of the enzyme binds to create an enzyme-substrate complex, a reaction occurs (catalysed by the enzyme) and then the products are released

Question 6

What does the statement ‘enzymes are highly specific’ mean?

Answer 6

The active site of the enzyme must bind to a substrate that has a complementary shape and so only specific reactions can be catalysed

Question 7

State 4 factors that affect the rate of an enzyme-controlled reaction

Answer 7

Temperature, pH, substrate concentration, enzyme concentration

Question 8

Describe the effect of temperature on the rate of an enzyme-controlled reaction

Answer 8

As the temperature increases, so does the rate of reaction
Once the temperature exceeds the optimum, the enzyme
denatures and the rate of reaction decreases

Question 9

Why does the rate of an enzyme-controlled reaction increase when the temperature increases?

Answer 9

As the temperature increases the particles have more kinetic energy
This increases the chance of collisions forming an enzyme substrate complex

Question 10

If temperature increases above the optimum, how does this affect enzyme function?

Answer 10

The active site will change shape and the enzyme denatures and so it will no longer fit the substrate

Question 11

Describe the effect of pH on the rate of an enzyme-controlled reaction

Answer 11

The rate of an enzyme catalysed reaction is fastest at the optimum pH. The change in pH will distort the enzyme’s active site (denaturing it) so that it can no longer fit the specific substrate.

If the pH is too high or low, the enzyme will work less efficiently and the active site may be denatured at extremes of pH