1.4 Factors affecting enzymes
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What are the four factors affecting rate?
Temperature, substrate concentration, pH and enzyme concentration.
Why does pH affect rate?
Because amino acids contain both basic and acidic groups, changes in the pH of a solution can change the bonding between amino acids and, therefore, cause changes to the secondary and tertiary structure of a protein.
Small changes in pH cause what?
Cause small reversible changes in enzyme structure – inactivation.
Large changes in pH cause what?
Permanent changes in the structure of the protein – denaturation.
What is changed by pH in enzymes?
Charges of the side groups - changing the ability of the enzyme’s active site to form bonds with a substrate.
As temperature changes, particles gain what energy?
Kinetic.
Up to the optimum temperature, bonds remain what?
Up to the optimum temperature for an enzyme, bonds remain intact and can form enzyme-substrate complexes as there is no change to the active site.
What happens past optimum temperature?
As temperature increases above the optimum, the increased heat gives more energy to particles. Bonds in the enzyme begin to vibrate and eventually they break – weak hydrogen bonds are broken first. Eventually, there is a loss of secondary and tertiary structure, the 3D shape of the active site changes and the active site can no longer form bonds with the substrate.
What is the effect of substrate concentration on rate?
If the amount of enzyme is constant the rate of reaction will increase as the substrate increases, but there must come a point when all the enzyme’s active sites are working to full capacity i.e. all the active sites are filled.
What is the effect of enzyme concentration on rate?
Increasing the enzyme concentration will increase the rate of reaction.
What is a competitive inhibitor?
This occurs when a substance has a close structural resemblance to a substrate molecule and can bind temporarily to the active site instead of the normal substrate.
What happens when a competitive inhibitor affects an enzyme?
This means that the active site is blocked for the substrate so the substrate cannot bind to the active site and there are fewer enzyme-substrate complexes and the rate of reaction is decreased.
Is a competitive inhibitor reversible?
Yes.
What happens if substrate concentration is increased whilst competitive inhibitors are present?
As substrate concentration is increased, there are fewer inhibitor molecules in proportion to the number of substrate molecules. Less competition occurs for the active site and the maximum rate of the enzyme-controlled reaction can be achieved.
What is a non-competitive inhibitor?
This occurs when a substance has no structural resemblance to a substrate molecule but binds to the enzyme at a point other than the active site. This is called the allosteric site.
Where does a non-competitive inhibitor bind to?
The allosteric site.
What does a non-competitive inhibitor do to an enzyme?
This changes the structure/3D shape of the active site. This means that the substrate cannot bind to the active site so fewer enzyme-substrate complexes are made and the rate of reaction is decreased.
Are non-competitive inhibitors reversible?
Some are, some aren’t.
Is the rate of reaction in non-competitive inhibitors affected by substrate concentration?
No, you cannot get back to the maximum rate of reaction by using higher concentrations of substrate.