Factors affecting enzyme activity

Enzyme activity at low temperatures

The rate of an enzyme-catalysed reaction is low because the enzyme and substrate have less kinetic energy. Therefore, there are fewer, less frequent collisions between the substrate and active site and fewer ESC form, so less substrate is converted into product.

Enzyme activity as temperature increases

As the temperature increases, the rate of reaction increases as more successful collisions occur between the substrate and active site to form more ESC, until the optimum temperature for the enzyme is reached when the rate of reaction reaches a maximum.

Enzyme activity above the optimum

As temperature increases above the optimum temperature the rate of reaction starts to decrease as the enzyme becomes denatured. The substrate can no longer bind to the active site to form an ESC. As a result, less substrate is converted into product so the rate of reaction decreases.

What occurs to enzymes at high temperatures

The kinetic energy of the enzyme increases, so the enzyme vibrates too much breaking the weak bonds e.g. hydrogen bonds that maintain the tertiary structure of the enzyme. Therefore, the enzyme changes shape and the active site changes shape (denatures).

Enzymes of extremophiles living at high temperatures

Tertiary structure is maintained by more strong covalent disulfide bonds and less hydrogen bonds.

Temperature coefficient

Refers to the increase in the rate of a process when the temperature is increased by 10°c.

How to calculate the temperature coefficient

Rate of reaction at (t + 10)°c / Rate of reaction at t°c.

Q₁₀ for enzyme-controlled reactions between 0°c and 40°c

Approximately 2, which means the rate of reaction doubles for every 10°c rise in temperature.

What does pH measure

Hydrogen ion/proton concentration.

Buffer

A substance that can accept or donate hydrogen ions to resist a change in pH.

Enzyme activity at extremes of pH

H⁺ ions disrupt the hydrogen and ionic bonds that maintain the tertiary structure of the enzyme. This causes the enzyme to denature and the active site to change shape so it is no longer complementary to the substrate.

How can H⁺ prevent substrate binding

They associate with certain amino acid R groups at the active site altering the charge distribution

Why must pH be maintained by homeostasis

Changes in pH can denature proteins and cause vasodilation/vasoconstriction.

How does increasing enzyme concentration initially affect enzyme activity

More active sites are available to bind to the substrate resulting in more frequent collisions between the active site and substrate, therefore more ESC form increasing the initial rate of reaction.

What eventually occurs to the rate of reaction as enzyme concentration increases

Reaches a Vmax as, substrate concentration becomes the limiting factor and some active sites are left unoccupied.

How does increasing substrate concentration initially affect enzyme activity

There will be more frequent collisions between the active sites and substrate, therefore more ESC form increasing the initial rate of reaction.

What eventually occurs to the rate of reaction as substrate concentration increases

Reaches a Vmax as enzymes concentration becomes the limiting factor and all active sites are occupied.