1.8 Factors affectng enzyme inhibition

Question 1

What are the requirements needed for an enzyme to act

Answer 1

. Come into physical contact with its substrate
. Have an active site which fits the substrate

Question 2

What two changes do we frequently measure to find the progress of an enzyme catalysed reaction

Answer 2

. Formation of products of the reaction

. Disappearance of substrate

Question 3

In the reaction of enzyme catalase acting on hydrogen peroxide, what would a graph of the formation of oxygen produced look like.

Answer 3

Positive curved correlation
_ Like that
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Explanation: At first there is lots of substrate (hydrogen peroxide) but no product (water, oxygen)
. So it’s easy for substrate molecules to come into contact with empty active sites on enzymes
. These active sites are all filled at any given moment and the substrate is rapidly broken down into its products
. Amount of substrate decreases as its broken down, and amount of products increase

As reaction proceeds there is less reactant and more product so it becomes more difficult for substrate molecules to come in contact with active sites because there are less substrates, and product molecules can get in the way, preventing them from reaching active sites.

Therefore it takes longer for substrate molecules to be broken down by the enzyme so its rate of disappearance slows. Graphs tail off.

Graphs flatten out when all substrate is used up so new new product is produced

Question 4

How do you measure the rate of change from a curved graph

Answer 4

. Measure the gradient at a chosen point: this is done by drawing a tangent along the graph at the point you want to measure the rate of reaction

. Find gradient by finding two points on tangent and doing

Change in y / change in x

Question 5

What is the term for the shapes of an active site and a substrate

Answer 5

They’re complimentary, not the same

Question 6

Why must all other variables be kept constant when measuring rate of reaction

Answer 6

To make it a fair test

Eg if measuring the effect of temperature on a reaction, the PH, enzyme concentration and substrate concentration must be kept constant

Question 7

Effect of warm temperature on enzyme action

Answer 7

. Increase in temp leads to increase in kinetic energy of molecules, so as a result they move around more rapidly and collide more.
This means enzyme and substrates come together more often forming more enzyme- substrate complexes
. So rate of reaction increases

Question 8

What happens when temperature gets too high (effect on enzyme action)

Answer 8

It starts to break hydrogen bonds in the enzyme molecule
This results in enzyme and active site changing shape so substrate can’t fit well into it, slowing the rate of reaction.
For human enzymes this happens at around 45 degrees

. At 60 degrees, enzyme is so disrupted that it stops working altogether, so is denatured.

Denaturation is a permanent change so once it has occurred, the enzyme doesn’t function again

Question 9

Why have our bodies evolved to be 37 degrees

Answer 9

. Although higher body temps increase the metabolic rate slightly, the advantages are offset by the additional energy (food)that would be needed to maintain the higher temperature

. Other proteins, apart from enzymes may be denatured at high temperatures

. At high temperatures, any further rise in temperature, eg during illness might denature the enzymes

Question 10

What is Ph

Answer 10

The Ph of a solution is the measurement of its hydrogen ion concentration.

Its calculated using PH= -log10[H+]

Every enzyme has an optimum Ph, the ph it works best at

Question 11

How does a change in PH effect enzyme action

Answer 11

. A change in PH alters the charges on the amino acids that make up the active site of an enzyme
As a result the substrate can no longer become attached to the active site, so the enzyme- substrate complex can no longer be formed

. Depending on how significant the change in PH is, it may cause the bonds maintaining the enzymes tertiary structure to break.
The active site therefore changes shape

Question 12

What is the arrangement of the active site determined by

Answer 12

. The hydrogen and ionic bonds between the -NH2 and -COOH groups of the polypeptides that make up the enzyme

Question 13

Why do enzymes work efficiently at low concentrations

Answer 13

. Once an active site has acted on its substrate it is free to repeat the procedure on another substrate molecule, which means that enzymes (being catalysts) are not used up in the reaction and therefore work efficiently at low concentrations.

Eg one enzyme molecule can act on millions of substrate molecules in one minute

Question 14

Effect of enzyme concentration on rate of reaction

Answer 14

. 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

Question 15

Effect of low enzyme concentration on rate of reaction

Answer 15

. There are too few enzyme molecules to allow all substrate molecules to find an active site at one time.

The rate of reaction is therefore only half the maximum possible for the number of substrate molecules available

Question 16

Effect of intermediate enzyme concentration on rate of reaction

Answer 16

. With twice as many enzyme molecules available, all the substrate molecules can occupy an active site at the same time.

The rate of reaction has doubled to its maximum because all active sites are filled

__________
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Question 17

Effect of high enzyme concentration on rate of reaction

Answer 17

. The addition of more enzyme molecules has no effect as there are already enough active sites to accommodate all the available substrate molecules.

There is no increase in rate of reaction

___________ _____
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Question 18

Effects of substrate concentration on the rate of enzyme action

Answer 18

If the concentration of enzyme is fixed and substrate concentration is slowly increased, rate of reaction increases in proportion to the concentration of the substrate.

Because at low substrate concentrations
the enzyme molecules have only a limited number of enzymes to collide with, and therefore the active sites of the enzymes are not working to full capacity

Question 19

Effect of low substrate concentration on rate of enzyme action

Answer 19

. There are too few substrate molecules to occupy all available active sites.
. The rate of reaction is therefore only half the max possible for the number of enzyme molecules available

Question 20

Effect of intermediate substrate concentration on rate of enzyme action

Answer 20

. All active sites are occupied at one time.
The rate of reaction has doubled to its maximum because all the active sites are filled

Question 21

Effect of high substrate concentration on the rate of enzyme action

Answer 21

The addition of further substrate molecules has no further effect as all active sites are already occupied at one time.

There is no increase in rate of reaction