Enzymes

Question 1

What are enzymes

Answer 1

Globular proteins which catalyse metabolic reactions

Question 2

What are the two types of enzymes

Answer 2

Enzymes which operate inside cells (intracellular enzymes) and enzymes which operate outside cells (extracellular enzymes)

Question 3

Lock and key hypothesis

Answer 3

The shape of the active sit allows the substrate to fit in perfectly. Each type of enzyme works on only one type of substrate molecule, because the active sites shape is specific to one substrate molecules.

Question 4

How an enzyme works

Answer 4

Random movement of substrate and enzyme brings the substrate into the active site. An enzyme-substrate complex is temporally formed. The R groups of the amino acid in the active site interact with the substrate. The interaction of the substrate with the active site breaks the substrate apart. An enzyme-product complex is briefly formed before the two product molecules leave the active site. The enzyme is unchanged.

Question 5

Induced fit hypothesis

Answer 5

The enzyme and the substrate are not exactly complimentary so they change shape slightly as the substrate molecule enters the enzyme in order to ensure a perfect fit.

Question 6

How do enzymes speed up reactions

Answer 6

They reduce the activation energy needed

Question 7

How is the substrate held in place by the enzyme

Answer 7

The substrate is held in place by temporary bonds which form between the substrate and some of the R groups of the enzymes amino acids.

Question 8

How can you investigate the progress of an enzyme-catalysed reaction

Answer 8

By measuring the rates of product formation, for example using catalase which causes the breakdown of hydrogen peroxide into water and oxygen. You can collect the oxygen to measure the rate of reaction. You can measure the rate of substrate disappearance, for example using amylase.

Question 9

The course of a reaction

Answer 9

When the enzyme and substrate molecules are first mixed there are a large number of substrate molecules. The enzyme always has a substrate molecule in its active site, so the rate of reaction is fast. However, as more and more substrate is converted into product there are fewer substrate molecules to combine with the enzyme, so there are less frequent collisions. The reaction gets slower and slower until as the substrate molecules are converted into product and it stops.

Question 10

The effect of enzyme concentration on the rate of reaction

Answer 10

The initial rate of reaction increases with increasing enzyme concentration, as the more enzymes present the more active sites available for the substrate to slot into and react with. They will all produce the same amount of product and level off at the same value as there was the same amount of reactant to start off with.

Question 11

When you compare reactions what do you look at

Answer 11

The initial rate of the reaction, the rate of reaction in the first 30 seconds on the Y axis and the thing you are measuring on the X axis.

Question 12

The effect of substrate concentration on enzyme activity

Answer 12

As substrate concentration increases the initial rate of reaction increases as the more substrate molecules there are the more often an enzymes active site will bond with one. However, there comes a point when adding more substrate will not affect the rate of reaction as the enzymes active site is working continuously and the substrate molecules are queuing up to use the active site.

Question 13

The effect of temperature on enzyme activity

Answer 13

At low temperature the rate of reaction is very slow. This is because the substrate and enzyme are moving very slowly so the substrate molecule will not often collide with the active site. As temperature increases there is more kinetic energy the enzyme and substrate molecule move faster and collisions happen more frequently, the activation is more likely to be overcome and there are more enzyme substrate complexes. However, above a certain temperature the enzyme denatures. The substrate molecule can no longer fit into the active site and the reaction stops. Initially it cant fit as well

Question 14

Optimum temperature

Answer 14

The temperature at which an enzyme catalyses a reaction at its maximum rate.

Question 15

The effect of ph on enzyme activity

Answer 15

At low Ph there is lots of hydrogen ions which can interact with the R groups of the amino acid and affect its three dimensional shape. The shape of the active site changes reducing the chances of the substrate molecule fitting in it. A ph very different from the optimum ph can denature an enzyme

Question 16

Competitive inhibitors

Answer 16

A competitive inhibitor has a similar shape to the substrate and fits into the enzymes active site, meaning that the substrate can not fit in an the reaction will not take place. It binds only briefly to the active site.

Question 17

How do competitive inhibitors affect the rate of reaction

Answer 17

There is competition between the substrate and the inhibitor for the active site. If there is much more substrate then the inhibitor, the substrate molecule will easily bind to the active site and the enzymes activity is not affected. If the inhibitor concentration increases it becomes less likely that the substrate molecule will collide with the active site.

Question 18

Non-competitive inhibitor

Answer 18

The inhibitor binds to another part of the enzyme which is not its active site. This distorts the enzymes three dimensional shape meaning that the substrate can not attach.

Question 19

Vmax

Answer 19

The maximum rate of reaction.

Question 20

Accurate graph to derive Km and Vmax

Answer 20

On the x-axis have one divided by substrate concentration and on the y-axis have one divided by velocity. One divided by the Vmax is the y intercept. Minus one divided by Km is the x intercept.

Question 21

Km

Answer 21

This is the substrate concentration at half Vmax, the higher the affinity for the enzyme for the substrate the lower the substrate concentration needed for this to happen.

Question 22

Enzyme affinity

Answer 22

Measured by Km. The higher the affinity the more likely a product will be formed when a substrate molecule enters the active site.

Question 23

Immobilising enzymes

Answer 23

You an immobilise an enzyme in alginate. You can reuse the enzyme and it keeps costs down. It easy to separate the enzyme from the mixture. Immobilised enzymes are more tolerant to temperature and ph change as the enzymes are held firmly in space by the alginate.