Factors Affecting Enzyme Action - 1.8 Flashcards
What are the two changes that are most frequently measured to observe enzyme action?
- The formation fo the products of the reaction, for example the volume of oxygen produced when the enzyme catalase acts on hydrogen peroxide.
- The disappearance of the substrate, for example the reduction in concentration of starch when it is acted upon by amylase.
How do we measure the rate of change in the rate of a reaction at any point on the curve of a graph?
Find the gradient at our chosen point.
What is the effect of temperature on enzyme action?
A rise in temperature increases the kinetic energy of molecules. As a result, the molecules move around more rapidly and collide with each other more often. In an enzyme-catalysed reaction, this means that the enzyme and substrate molecules come together more often in a given time. there are more effective collisions resulting in more enzyme-substrate complexes being formed and son the rate of reaction increases.
What happens to the bonds in enzymes as the temperature increases?
The temperature rise begins to cause the hydrogen and other bonds in the enzyme molecule to break. At first, the substrate fits less easily into this changed active site, slowing the rate of reaction. for many human enzymes this may begin at temperatures of around 45 degrees.
What happens to enzymes at around 60 degrees?
The enzyme is so disrupted that it stops working altogether. It is said to be denatured.
What is denaturation?
A permanent change in the enzyme and, once it has occurred, the enzyme does not function again.
How does pH affect how an enzyme works?
- A change in pH alters the charges on the amino acids that make up the active site of the enzyme. As a result, the 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.
What determines the arrangement of the active site?
The hydrogen and ionic bonds between -NH2 and -COOH groups of the polypeptides that make up the enzyme. The changes in H+ ions affects this bonding, causing the active site to change shape.
pH fluctuations inside organisms are usually small, what does this mean for enzyme action?
The changes in pH are far more likely to reduce an enzyme’s activity than to denature it.
What is the effect of enzyme concentration on the rate of reaction?
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. If you therefore increase the enzyme concentration, some of the excess substrate can now also be acted upon and the rate of reaction will increase.
If, however, the substrate is limited, then any increase in enzyme concentration will have no effect on the rate of reaction. The rate of reaction will therefore stabilise at a constant level, meaning the graph will level off.
What is the effect of substrate concentration on the rate of enzyme reaction?
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.
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. After that, the addition of more substrate will have no effect on the rate of reaction. When there is an excess of substrate, the rate of reaction levels off.
