Topic 1 - Year 1 - Biological Molecules - Enzymes

Question 1

What is an enzyme?

Answer 1

An enzyme is a protein that speeds up the rate of a chemical reaction. Therefore an enzyme is a biological catalyst.

Question 2

Why are enzymes referred to as biological catalysts?

Answer 2

Enzymes are known as biological catalysts as they speed up the rate of metabolic reactions.

Question 3

Which part of an enzyme does the substrate bind to?

Answer 3

A substrate binds to the active site of an enzyme.

Question 4

What is a substrate?

Answer 4

A substrate is the substance that the enzyme interacts with.

Question 5

Why does each enzyme fit a complimentary fit to different substrates?

Answer 5

Each enzyme has a complimentary fit yo a different substrate as each enzyme has a different tertiary structure hence different 3 dimensional shape. the 3 dimensional shape thus alters the shape of the active site and substrates may only bind to the active site if they have a specific and complimentary fir to it.

Question 6

How do you refer to the amount of energy needed to start a chemical reaction?

Answer 6

Activation energy

Question 7

How do enzymes speed up reactions?

Answer 7

Enzymes speed up reactions by lowering the activation energy that is needed to start the reaction.

The activation energy is lowered because , when a substrate fits an enzyme an enzyme substrate complex is formed.

In reactions where bonds are being made the enzyme lowers the activation energy as it attracts substrate molecules , this bring the substrate molecules close together and holds them there , this reduces any repulsion between them and allows them o bond more easily meaning less energy is required in the bonding process.

In reactions where bonds are being broken activation energy is lowered as when a substrate forms an enzyme substrate complex it puts strain on the enzymes bonds , this means the substrate molecule breaks up more easily which means less energy is required for the breaking of the bonds.

Question 8

What is formed when an substrate binds to the active site of an enzyme?

Answer 8

An enzyme substrate complex (ES complex)

Question 9

What is a metabolic reaction?

Answer 9

A metabolic reaction is a chemical reaction that occurs inside a living organisms to keep the organism alive.

Question 10

The active site is a dent or depression in the 3 dimensional structure of an enzyme, an enzyme is a protein thus a polypeptide chain made up of amino acid monomers, which part of the amino acids active site?

Answer 10

The R group of the amino acids in the polypeptide chain line the active side of an enzyme.

Question 11

Explain the lock and key model

Answer 11

The lock and key model dictates that enzymes and a substrate will only form an enzyme substrate complex if the substrate has an exact complimentary fit to the active site of the enzyme , the substrates shape must be specific and complimentary if it is to successfully bind with the enzyme and form an enzyme substrate complex.

Question 12

Explain the induced fit model

Answer 12

The induced fit model helps to explain why enzymes are so specific and only bond to one particular substrate. The substrate doesn’t only have to have the right complimentary shape to the enzyme but it also must have the ability to make the shape of the active site change , this helps the substrate to be more securely locked in

Question 13

How is the lock and key model different from the induced fit model.

Answer 13

While in the lock and key model the enzymes active site has a fixed shape that the enzyme must bind to to form n ES complex , in the induced fit model the enzymes active site has a degree of flexibility so can slightly change shape to secure the locking of the substrate into the enzymes active site.

Question 14

Why do enzymes only normally catalyses one reaction ?

Answer 14

Enzymes normally only catalyse one reaction due to their tertiary structure . Their tertiary structure decides the shape of the active site and the active site has a complimentary fit (normally) to a single substrate hence the enzyme only catalyses a single reaction.

Question 15

What would happen if a mutation occurred in the genes that coded for an enzyme?

Answer 15

If a mutton occurred in the genes that coded for an enzyme then the sequence of amino acids strung together would alter , this would mean that the primary structure would change which ultimately would alter the 3 dimensional tertiary structure, this change in structure would alter the shape of the active site and mean that a substrate may no longer be able to bind this means no ES compels would be formed and the reaction would not be cataylised.

Question 16

What change in the rate of reaction would indicate that enzyme activity is high?

Answer 16

If the rate of reaction is high it implies that the enzyme activity is also high.

Question 17

What change in the rate of reaction would indicate that enzyme activity was low?

Answer 17

A decrease in rate of reaction would indicate that enzyme activity is low.

Question 18

State two ways in which rate of reaction can be measured:

Answer 18

1 . How fast is the product being made
A measure of rate of reaction can be calculated through recording how much product is being made, there are different molecules present at the beginning of a reaction than there are at the end of a reaction, by measuring the amount of end product present at different times during the reaction the rate of reaction can be calculated.

2. How fast the substrate is broken down
   A measure of rate of reaction can be calculated through recording how many substrate molecules remain at different times.In a reaction the substrate molecules are used up hence by looking at how many have yet to be used up you can calculate the rate of reaction.

Question 19

How does Temperature affect Enzyme Activity?

Answer 19

As Temperature increases enzyme activity also increases up until a point. Beyond this point (the temperature is different among different enzymes) temperature increase has a negative impact on enzyme activity . As temperature increases the kinetic energy of each particle increases , this means enzymes and substrates move more quickly and in consequence the substrates are more likely to collide with the enzymes active sites. Also as the particles have more energy they collide more forcefully which is more likely to result in a reaction.

If the temperature gets too hot the reaction stops. The reaction stops because the enzyme gets so much kinetic energy and consequently starts to vibrate , the vibrations break some of the bonds that hold the enzyme in shape this changes the shape of the active site and and hence the enzyme and the substrate no longer form an ES complex . At this point the enzyme is said to be denatured.

Question 20

What is optimum temperature?

Answer 20

Optimum temperature is the temperature at which the reaction happens at the quickest rate , the temperature is at its optimum when it is giving enzymes and substrates enough energy to increase their movement and increase the force with which they collide however not enough to cause excessive vibrations in the enzymes which would cause the bonds in the tertiary structure to break denaturing the enzyme.

Question 21

How does pH affect enzyme activity ?

Answer 21

Each enzyme has an optimum pH , in acidic pH’s (pH 1-6) there are H+ ions , in alkaline pH’s (pH - 8-14) there are OH- ions, if an enzyme is removed from the small range of pH’s it works within it may stop functioning as the ions found in acids and alkalis can disturb the ionic bonds and the hydrogen bonds which hold the tertiary structure of the enzyme , this causes the tertiary structure to denature. Once the original structure is lost it cannot re-form so nothing will bind to the denatured enzyme.

Question 22

How does substrate concentration affect enzyme activity?

Answer 22

The higher the substrate concentration the greater the rate of reaction , up until the saturation point. If there are more substrate molecules then there will be more collisions between the substrate and enzyme’s active site, this means it is more likely that the enzymes active site will be occupied and hence the rate of reaction will be quicker as more enzyme substrate complex will be being formed. Therefore there is a positive correlation. . At a point the graph will plateau , when the graphs plagued the reaction is likely to have reached its saturation point , the saturation point is reached when all the enzymes active sites are being occupied hence adding more substrate has no effect so the graph levels , the graph levels because the enzyme concentration has become a limiting factor preventing the rate of reaction from continually increasing.

Question 23

How does enzyme concentration affect enzyme activity?

Answer 23

Enzyme concentration and enzyme activity positively correlate as the enzyme concentration increases the rate of reaction also increases as the chances of a collision between a substrate and the active site of an enzyme are increased hence there are likely o be be more ES complex’s formed. So increasing the enzyme concentration increases the rate of reaction. A graph detailing this correlation may plateau after a point as the substrate concentration may become the limiting factor , in this case increasing enzyme concentration will have no further effect.

Question 24

What is a competitive inhibitor?

Answer 24

Competitive inhibitor molecules have a similar shape to that of the substrate , hence the inhibitor molecule also has a complimentary fit to an enzymes active site. A competitive inhibit competes with the substrates to bind with the active site of the enzyme however when this binding occurs no reaction takes place but it prevents other reactions from taking place , therefore in the presence of competitive inhibitor the rate of reaction is slowed.

Question 25

What is a non competitive inhibitor?

Answer 25

A non competitive inhibitor is a molecule that binds with an enzyme but does not bind at the active site. The binding of a non competitive inhibitor changes the shape of an active site so the substrate molecule can no longer bind to it, this slows the rate of reaction as it prevents the formation of enzyme substrate complex’s.

Question 26

What is the difference between a competitive inhibitor and a non competitive inhibitor?

Answer 26

1. With a competitive inhibitor the decrease in rate of reaction can be minimised by adding more substrate (increasing substrate concentration) as this mean there is a greater likely hood that an ES complex will for than the likelihood of an enzyme being inhibited where as with non-competitive inhibitors increasing the substrate concentration won’t make any difference the enzymes will still be inhibited as the shape of their active sites will be changed and the rate of reaction in presence of a competitive inhibitor will be a lot slower.

Question 27

From looking at a curved graph of rate of reaction how do you work out a rate of reaction at a certain point in time?

Answer 27

You draw a tangent to the curve at that particular time and work out the gradient of this tangent using change in y over change in x , the answer to this calculation will give you the rate of reaction, the units for rate of reaction are normally cm^3s^-1.

Question 28

Are enzymes used up in reactions?

Answer 28

Enzymes are never used up in reactions once the substrate is broken down it leaves the active site and the enzyme can then be used again.

Question 29

At which point is an enzyme said to be denatured?

Answer 29

An enzyme is said to be denatured at the point when it no longer functions as a catalyist in consequence of an inability to for enzyme substrate complex’s

Question 30

What is optimum pH?

Answer 30

Optimum pH is the pH at which the enzymes function most efficiently.

Question 31

What is saturation point in terms of enzymes?

Answer 31

Saturation point is the point at which no more enzyme substrate complex can be formed as all the enzymes active sites are being occupied.

Question 32

What is meant by “the graph plateaus”?

Answer 32

Plateauing is the process of the graph levelling out

Question 33

What determines how much of an effect using a competitive inhibitor will have?

Answer 33

How much the enzyme gets inhibited depends on the relative concentrations of enzyme and substrate. Enzymes with less inhibitor in relation to the amount of substrate will have a quicker rate of reaction