Question

What is the energy of activation? 16. How do enzymes speed the rate of reaction? 17. Talk about the effect of the following on enzyme reaction rate: a) Substrate concentration b) pH c) Temperature 18. How do vitamins play a part in enzymatic reactions?

Answer 1

Factors affecting enzyme activity

1. Substrate concentration

Increase in the substrate concentration increases the activity of the enzyme until all the active sites of the enzyme molecule are saturated with the substrate.

Ø After this saturation the rate of enzymatic reaction becomes steady.

Ø Then, the addition of the substrate will not have a positive effect on the velocity of reaction.

Ø Higher concentration of substrate can nullify the effects of competitive inhibitors in the medium.

2. pH

Enzymes are active only over a limited range of pH.

Ø Most of the enzymes are specific to a particular pH.

Each enzyme will have an optimum pH where the velocity of the reaction is maximum.

Ø A bell-shaped curve is obtained for the effect of pH and enzymatic activity.

Ø Hydrogen ions in the medium influence the ionic charges on the amino acids in the enzymes particularly on the active site.

3. Temperature

The enzymatic activity will be optimum at normal temperature.

Ø At very low temperature the activity of enzyme will be minimal or zero.

Ø The increase in temperature (up to a certain limit) can increase the enzyme’s catalytic activity.

The maximum activity is observed between 30 to 45ºC for most of the enzymes.

Ø Beyond 45ºC the enzyme activity is reduced drastically.

Ø Beyond 60-70ºC the enzymes were denatured.

Ø Temperature coefficient or Q10: Increase in the velocity of enzymatic reactions when the temperature is increased by 10°C.

Ø The Q10 of majority of enzymes will be 2 at a temperature between 0 and 40°C.