Biological molecules: Enzymes

Question 1

What are enzymes?

Answer 1

Globular proteins which act as catalysts

Question 2

What are catalysts?

Answer 2

Substances that alter the rate of a chemical reactions without undergoing permanent change themselves and can be reused repeatedly making them effective in small amounts

Question 3

What do enzymes actually do that helps them speed up the rate of reactions?

Answer 3

They reduce the activation energy and therefore allow reactions to take place at a lower temperature than normal

Question 4

What are anabolic enzymes?

Answer 4

Enzymes that build up the substrate (so condensation reactions occur)

Question 5

What are catabolic enzymes?

Answer 5

Enzymes that break down the substrate (so hydrolysis reaction occurs)

Question 6

What is it called when the substrate neatly fits into the active site?

Answer 6

The enzyme-substrate complex (THIS IS A KEY WORD)

Question 7

How is the substrate molecule held within the active site?

Answer 7

Via bonds that temporarily form between the R groups of certain amino acids in the active site and groups on the substrate molecules

Question 8

What does it mean that enzymes have a high turnover rate?

Answer 8

They allow lots of reactions to occur per second

Question 9

What does the induced fit model of enzyme action suggest?

Answer 9

The active site is flexible and the proximity of the substrate causes the active site to mould around the shape of the substrate.

Question 10

What’s the explanation behind the induced fit model of enzyme activity?

Answer 10

The enzyme’s active site moulds into shape as the enzyme puts a strain on the substrate molecule and this strain distorts a particular bond or bonds in the substrate and consequently lowers the activation energy needed to break the bond.

Question 11

What did the lock and key model of enzyme action suggest?

Answer 11

That the shape of the active site was exactly complimentary to the shape of its specific enzyme like the lock of a key.

Question 12

How is the lock and key model limited?

Answer 12

It considers an enzyme to be a rigid structure however scientists observed that other molecules could bind to enzymes at sites other than the active site which altered the activity of the enzyme and so suggested that the enzymes shape was being altered by the binding molecule and so the structure wasn’t rigid but instead flexible

Question 13

What are the 3 steps to take to get full marks on exam questions that are about how a particular factor affects the rate of an enzyme controlled reaction?

Answer 13

1. Talk about how the factor is affecting the frequency of successful collisions.
2. Talk about how the factor is affecting the number of enzyme substrate complexes being formed
3. Therefor state how the factor is affecting the rate of reaction

Question 14

What is the pH?

Answer 14

A measure of H+ ion concentration

Question 15

What is the H+ ion concentration in a substance with pH 7?

Answer 15

H+ = 1 x 10 to the minus 7

Question 16

How do you measure the process of an enzyme catalysed reaction?

Answer 16

By measuring its time course (how long it takes for a particular event to run its course)

Question 17

What are the two changes most frequently measured in enzyme catalysed reactions?

Answer 17

• The formation of products of the reaction

- the disappearance of the substrate

Question 18

What are the two reasons a change in pH can affect enzyme activity?

Answer 18

• changes in the pH can change the charge of the R groups in the active site and so affect the binding of the substrate to the active site
• changes in the pH can also change the charge of the R groups in the protein and affect the H bonds and ionic bonds that stabilise the tertiary structure leading to denaturation

Question 19

Explain how enzyme concentration affects the rate of enzyme controlled reactions

Answer 19

Enzyme concentration is directly proportional to the rate of reaction as an increase in enzyme concentration means there’ll be more successful collisions happening and so more enzyme substrate complexes will be formed, catalysing more reactions in a smaller space of time, hence increasing the rate of reaction

Question 19

Explain how substrate concentration affects the rate of enzyme controlled reactions

Answer 19

Substrate concentration increasing causes the rate of reaction to increase until a certain point where any more enzymes will have no effect on the rate of reaction. This is because initially, more substrate molecules increases the rate of successful collisions and so allowing for many enzyme substrate complexes to be formed. The rate of reaction then stops increasing as the enzymes become saturated with the substrate as the maximum amount of enzyme substrate complexes are being formed because there is not enough enzyme to deal with all the substrate and therefore the rate of reaction no longer increases unless if more enzyme is added.

Question 20

Explain how pH affects the rate of enzyme controlled reactions

Answer 20

As the pH increases the frequency of successful collisions also increases and so increasing the rate of reaction, until the optimism pH is reached. Here the charges of the R groups in the active site start to change and so affect how the substrate binds to the active site, reducing the enzyme substrate complexes being formed and therefor causing the rate of reaction to decrease

Question 21

Explain how temperature affects the rate of enzyme controlled reactions

Answer 21

As the temperature increases, the molecules are moving a lot faster as they gain a higher store of kinetic energy. This causes the faster moving substrates to increase the frequency of successful collisions with the active site and so increasing the number of enzyme substrate complexes being formed. The optimum temperature is where the most enzyme substrate complexes are being formed. As the temperature continues increasing, the tertiary structure denatures, loosing the shape of the active site and so reducing the rate of reaction

Question 22

What is an enzyme inhibitor?

Answer 22

A substance that directly or indirectly interferes with the functioning of the active site of an enzyme

Question 23

What is a competitive inhibitor?

Answer 23

Where the inhibitor competes with the substrate for the active site

Question 24

What is a non competitive inhibitor?

Answer 24

Where the inhibitor binds to an allosteric site of an enzyme, changing the shape of the active site

Question 25

What is an allosteric site of an enzyme

Answer 25

A site on the enzyme that’s not the active site

Question 26

Give three points about competitive inhibitors

Answer 26

• they have a similar shape to the substrate allowing them to bind to the active site and occupy it causing the inhibitor to complete with the substrate for the active site
• the binding of a competitive inhibitor isn’t permanent so when it leaves the active site, another molecule can enter
• if there’s a high enough substrate concentration, the competitive inhibitors probability of binding with the substrate becomes negligible

Question 27

How can you reduce the likelihood of a competitive inhibitor binding to an enzyme?

Answer 27

By increasing the substrate concentration because its the difference between the concentration of the inhibitor and the substrate concentration that determines the inhibitor’s effect on the enzyme

Question 28

How do non competitive inhibitors stop the enzyme substrate complex from forming?

Answer 28

they attach themselves to the enzyme at an allosteric site causing a change uh the tertiary structure of an enzyme and so changing the active site in a way that the substrate still fits but not in the way that allows the reaction to proceed.

Question 29

What happens to the rate of reaction if you increase the substrate concentration in the presence of a non competitive inhibitor?

Answer 29

The rate of reaction will stay lowered because the substrate isn’t competing with the non competitive inhibitor for the active site

Question 30

What’s the competitive inhibitors effect on the rate of reaction if you increase the substrate concentration?

Answer 30

The effect reduces as the rate of reaction will eventually reach the same point as that of there being no inhibitor

Question 31

What is a metabolic pathway?

Answer 31

A series of reactions in which each step is catalysed by an enzyme

Question 32

Draw the diagram that shows negative feedback in metabolic pathways

Answer 32

Check biology album

Question 33

Why is the sequence of metabolic pathways very precise?

Answer 33

because the product of one reaction is the substrate for the next reaction