79 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.4 Enzymes And Biological Reactions) Flashcards
How does substrate concentration affect the rate of reaction?
The rate of an enzyme-catalysed reaction varies with changes in substrate concentration.
If the enzyme concentration is constant, the rate of reaction increases as the substrate concentration increases.
At low substrate concentrations the enzyme molecules have only a few substrate molecules to collide with so the active sites are not working to full capacity.
With more substrate, more active sites are filled.
The concentration of substrate is controlling the rate of reaction and so it is a limiting factor.
As even more substrate is added, at a critical concentration, all the active sites become occupied and the rate of reaction is at its maximum.
When all the active sites are full the enzyme is said to be saturated.
Even if more substrate is added, reactions cannot be catalysed any faster and so the line plateaus.
The substrate concentration is no longer controlling the rate of reaction so it is no longer a limiting factor.
Some other factor controls the rate of action, such as temperature.
Why a low enzyme concentration is sufficient to catalyse a large number of reactions?
Once a product leaves the active site, the enzyme molecule can be reused, so only a low enzyme concentration is needed to catalyse a large number of reactions.
How does enzyme concentration affect the rate of reaction?
As the enzyme concentration increases, there are more active sites available and therefore the rate of reaction increases.
What is the turnover number?
The number of substrate molecules that one enzyme molecule can turn into products in a given time is the turn-over number.
Describe catalase.
It is one of the fastest-acting enzymes known.
It has a turn- over number of 40 million molecules per second.
It breaks down the highly toxic waste, hydrogen peroxide.
In enzyme experiments, a buffer must be used.
Buffers maintain a constant pH, even when the products of the reaction are acid or alkaline.
Buffers may be thought of as absorbing extra hydrogen ions or hydroxide ions.
Limiting factor (Key-Term)
A factor that, when in short supply, limits the rate of a reaction. An increase in the value of a limiting factor causes an increase in the rate of reaction.
If temperature and pH are optimal and there is an excess of substrate, the rate of reaction is directly proportional to———
If temperature and pH are optimal and there is an excess of substrate, the rate of reaction is directly proportional to the enzyme concentration.
Draw a graph to show the effect of substrate concentration on the rate of reaction
Draw a diagram to show the effect of low and high substrate concentration on the rate of reaction
