1.8 - Factors affecting enzyme action Flashcards
What is required in order for an enzyme to work?
- Physical contact with substrate
2. An active site which fits the substrate
How can we measure the progress of a enzyme-catalysed reaction?
To measure the progress of an enzyme-catalysed reaction we usually measure its time-course, that is how long it takes for a particular event to run its course.
What two changes are most frequently measured in an enzyme-catalysed reaction?
- the formation of the products of the reaction
2. the disappearance of the substrate
Give an explanation for the shape of an enzyme-catalase graph.
- At first there is a lot of substrate but no product
- It is very easy for substrate molecules to come into contact with the empty active sites on the enzyme molecules.
- All enzyme active sites are filled at any given moment and the substrate is rapidly broken down into its products.
- The amount of substrate decreases as it is broken down, resulting in an increase in the amount of product.
- As the reaction proceeds, there is less and less substrate and more and more product.
- It becomes more difficult for the substrate molecules to come into contact with the enzyme molecules because there arc fewer substrate molecules and also the product molecules may ‘get in the way’ of substrate molecules and prevent them reaching an active site.
lt therefore takes longer (or the substrate molecules to be broken down by the enzyme and so its rate of disappearance slows, and consequently the rate of format ion of product also slows. Both graphs ‘tail off’.
How do we measure rate of change on a graph?
- Draw a tangent at point x
2. Using this line you can find the gradient
How do we investigate effect of a named variable on rate of reaction?
When investigating the effect of a named variable on the rate of an enzyme reaction all the other variables must be kept constant. For example, if measuring the effect of temperature, then pH, enzyme concentration and substrate concentration must be kept constant and all possible inhibitors should be absent.
What is the correct term for an active site and substrate that “match”
Complementary
Effect of temperature on enzyme action?
rate of reaction increases up to the optimum temperature as the kinetic
energy of the enzyme increases. Above the optimum temperature rate of reaction
decreases as the enzyme becomes denatured.
Effect of PH on enzyme action?
The pH of a solution is a measure of the hydrogen ion concentration. The pH of a
solution can be calculated using the following formula: pH = -log10[H+]. A hydrogen ion
concentration of 1x10⁻⁹ therefore has a pH of 9. pH affects the enzymes shape as it can
disrupt the bonds in the tertiary structure of the enzyme. Like temperature all enzymes
work at different optimum pH’s e.g. pepsin in the stomach works in very acidic
conditions.
What is the optimum temperature for most enzymes?
37ºC - body temperature
How does PH affect the structure of proteins?
A change in pH alters the charges on the amino acids that make up the active site of the enzyme. As a result, 1he substrate can
no longer become attached to the active site and so the enzyme substrate complex cannot be formed.
Depending on how significant the change in pH is, it may cause the bonds maintaining the enzyme’s tertiary structure to break. The active site therefore changes shape.
Effect of enzyme conc on the rate of reaction.
Once an active site on an enzyme has acted on its substrate, it is free to repeat the procedure on another substrate molecule. This means that enzymes, being catalysts, are not used up in the reaction and therefore work efficiently at very low concentrations.
As long as there is an excess of substrate. an increase in the amount
of enzyme leads to a proportionate increase in the rate of reaction.
A graph of the rate of reaction against enzyme concentration will initially show a proportionate increase. This is because there is more substrate than the enzyme’s active sites can cope with.
Effect of substrate concentration on the rate of enzyme action.
If the concentration of enzyme is fixed and substrate concentration
is slowly increased, the rate of reaction increases in proportion to
the concentration of substrate. This is because, at low substrate concentrations, the enzyme molecules have only a limited number
of substrate molecules to collide with, and therefore the active sites
of the enzymes are not working to full capacity. As more substrate is added, the active sites gradually become filled, until the point where all of them are working as fast as they can.
Explain why enzymes function less well at lower temperatures.
To function, enzymes must physically collide with their substrate. Lower temperatures decrease
the kinetic energy of both enzyme and substrate molecules, which then move around less quickly.
They hence collide less often and therefore react less frequently.
Explain how high temperatures may completely prevent enzymes from functioning
The heat causes hydrogen and other bonds in the enzyme molecule to break. The tertiary structure of the enzyme molecule changes, as does the active site. The substrate no longer firs the active site.
