Factors affecting enzyme activity

What affect does increase in temperature have on enzyme activity? 


Will result in more frequent successful collisions between substrate and enzyme, leading to an increase in the rate of reaction

What is the temperature co-efficient?


(Q10)

Is a measure of how much the rate of reaction increases with a 10 degree Celsius rise in temperature.

For enzyme controlled reactions, is taken as 2, meaning the rate of reaction doubles with a 10 degree Celsius temperature increase

How to work out the temperature co-efficient?

Q10 = R2 ÷R1 

R2 = rate at higher temperature

R1 = rate at lower temperature

What is meant by the optimum temperature?

• Temperature at which the enzyme has the highest rate of activity.

• The rate of reaction continues to increase until it reaches this point

• The enzyme-controlled reaction is at its fastest

• The decrease in the rate of reaction below the optimum temperature is less rapid due to the enzymes being less active

When will an enzyme be denatured, in terms of temperature?

When they are in temperatures higher than the optimum

What happens while and when an enzyme is being and is denatured?

• The bonds holding the enzyme together vibrate more

• As the temperature increases, so do the vibrations until the bonds strain and then break

• This results in a change in the tertiary structure of the protein, changing its shape, and the enzyme is said to be denatured

  • The active site changes shape and is not complementary to the substrate

  • Substrate can't fit into the active site, and enzyme cannot function as a catalyst

What affect does pH have on enzyme activity?


pH affects enzyme activity by altering the enzyme's shape and charge, which can impact its ability to bind to substrates and function optimally.

• The active site will be in the right shape at certain hydrogen concentrations which is the optimum pH

What is renaturation?

When the pH returns to its optimum, the protein (enzyme) will resume its normal shape and catalyze the reaction again

When is the enzyme said to be denatured in terms of pH?


When the pH changes more significantly where the structure is irreversibly altered and the active site is no longer complementary to the substrate

The substrate cannot bind to the active site, enzyme cannot carry out its function, reducing rate of reaction

How does pH affect R-groups interacting with each other?


The lower the pH (more hydrogen ions), the less the R-groups present on the amino acids forming the primary structure are able to interact with each other, leading to bonds breaking and the shape of the enzyme changing

This therefore means the shape of an enzyme changes as pH changes, and enzymes will only function in a narrow pH range

What is the effect of substrate concentration on enzyme activity?

Leads to a higher collision rate and enzyme-substrate complexes, increasing rate of reaction

Increases up to its maximum rate (Vmax)

All active sites are occupied - no more enzyme-substrate complexes can be formed until products are released

What is the effect of enzyme concentration on enzyme activity?


Leads to an increase in available active sites, so the more likely it is for a substrate to bind with one and a enzyme-substrate complex to be formed.

The reaction rate can rise to a higher Vmax , but then the substrate concentration will be the limiting factor, and the reaction rate will not increase until more substrate is added

Adding more enzymes will have no further effect if substrate is limited