4.2 Factors Affecting Enzyme Activity Flashcards
What are the factors that affect enzyme activity ?
Temperature
pH
Enzyme concentration
Substrate concentration
How do different temperatures affect enzyme activity?
Increased temperature increases kinetic energy of particles. Particles move faster and collide more frequently. Increased frequency of successful collisions between the substrate and enzyme. This leads to an increase in the rate of reaction.
What is the temperature coefficient ?
Q10
It is a measure of how much the rate of a reaction increases with a 10°C rise in temperature.
It is usually 2, so rate of reaction doubles every 10°c increase.
What happens if the temperature is too high?
At higher temperature the bonds holding the protein together vibrate more. As the temperature increases, the vibrations increase until the bonds strain and break.
This results in a change in the precise tertiary structure of the protein. The enzyme has changed shape and is said to have been denatured.
The active site has changed shape and is now longer complementary to the substrate and so can’t function as a catalyst.
What is the optimum temperature?
The temperature at which the enzyme has the highest rate of activity.
Once the enzymes have denatured above the optimum temperature, the decrease in rate of reaction is rapid. There only needs to be a slight change in shape of the active site for it to no longer be complementary.
Th decrease in the rate of reaction below optimum temperature is less rapid as it has not denatured, it it just less active.
How are enzymes adapted to cold temperatures?
More flexible structures, particularly at the active site, making them less stable than enzymes working at higher temperatures. Smaller temperature changes will denature them.
Describe enzymes working at high temperatures
More stable than enzymes at lower temperatures due to the increased number of bonds, particularly hydrogen bonds and sulfur bridges in their tertiary structures.
The shapes of these enzymes and their active sites are more resistant to change as the temperature rises.
How does pH affect enzyme activity ?
A change in pH refers to a change in hydrogen ion concentration. More hydrogen ions are present in low pH environments and fewer hydrogen ions are present in high pH environments.
Hydrogen bonds and ionic bonds hold proteins in their precise three - dimensional shape.
When the pH changes significantly the structure of the enzyme is irreversibly altered and the active site will no longer be complementary to the substrate. It has denatured, and rate of reaction decreases.
What is the optimum pH?
The pH at which the active site will in the right shape at is the optimum pH.
When the pH changes from the optimum , the structure of the enzyme and therefore the active site, is altered.
However if the pH returns to the optimum then the protein will resume its normal shape and catalyse the reaction again (renaturation ).
Why do enzymes only work in a narrow pH range?
The more hydrogen ions present, the less the R groups are able to interact with each other. This leads to bonds breaking and the shape of the enzyme changing.
This means the shape of an enzyme will change as the pH changes and therefore it will only function in a narrow range.
How does substrate / enzyme concentration effect enzyme activity ?
When substrate concentration is increased, the number of substrate molecules, atoms or ions in a particular area or volume increases. This leads to a higher collision rate with the active sites of enzymes and the formation of more enzyme substrate complexes. The rate of reaction increases.
This also happens with increased enzyme concentration. It increases the number of available active sites in a particular area or volume, leading to the formation of enzyme substrate complexes at a faster rate.
What is Vmax?
The point that rate of reaction can increase up to.
At this point all of the active sites are occupied by substrate particles and no more enzyme substrate complexes can be formed until products are released from active sites.
