Enzymes

Question 1

What is an enzyme?

Answer 1

A biological catalyst which changes the rate of a reaction without being broken down/used up in the process and without changing the substrate produced
-They control the rate of individual reactions within each cell

Question 2

Exam technique on the function of an enzyme

Answer 2

1. Enzymes are biological catalysts/define a catalyst
2. They aren’t used up/broken down in a reaction
3. They form an enzyme substrate complex
4. They lower the activation energy within a reaction

Question 3

Exam technique on enzyme substrate complexes

Answer 3

1. The enzymes active site is similar/complimentary to the substrate
2. When an enzyme substrate complex is formed the activation energy of a reaction is lowered
3. Link it to the question/example - what is produced/what has changed in the reaction?

Question 4

What is the structure of an enzyme?

Answer 4

-They are proteins made from amino acids
-The amino acids are held together with peptide bonds
-The amino acids fold into alpha helices or beta pleated sheets
-Formed in either: primary, secondary, tertiary or quaternary structures
-These amino acids code for different proteins and therefore different enzymes
-These structures are held together with either: hydrogen, ionic and disulphide bonds

Question 5

Exam technique on the structure of an enzyme

Answer 5

1. Mention that enzymes are globular proteins/define globular protein
2. Enzymes are proteins made up from amino acids
3. Amino acids are held in place by peptide bonds
4. Mention that amino acids fold into different structures which is why enzymes are all different
5. The tertiary structure is what defines the active site shape

Question 6

What is a globular protein?

Answer 6

Proteins that generally have a more compact and rounded shape and have functional roles (they do something)

Question 7

What is an anabolic reaction?

Answer 7

A reaction which builds up new chemicals

Question 8

What is a catabolic reaction?

Answer 8

A reaction which breaks down substances

Question 9

What does optimum mean?

Answer 9

Where the enzyme is most efficient, this changes depending on where the enzyme is located

Question 10

How does pH affect an enzyme?

Answer 10

It denatures when the pH is too high, this is because the bonds have been broken due to the interactions with the R groups
-This causes the enzyme to change shape and no enzyme substrate can be formed

Question 11

What does the rise on graph show?

Answer 11

That more activation energy is required to reach the optimum and all other factors must be kept constant

Question 12

What happens when an enzyme is at its optimum temperature?

Answer 12

The enzyme is working in its ideal condition, this means there is a lot of kinetic energy resulting in more successful collisions to form an enzyme substrate complex
-This means there is a high rate of reaction

Question 13

How does substrate concentration affect enzymes?

Answer 13

The graph levels off as most substrates have formed an enzyme substrate complex so there are less active sites to bind with, this will eventually stop when there are no more to bind with

Question 14

How does substrate concentration affect the rate of the reaction?

Answer 14

-Low substrate concentration = low rate of reaction
-High substrate concentration = high rate of reaction

Question 15

Exam technique on factors affecting the rate of an enzyme reaction

Answer 15

1. Mention the optimum/define optimum
   -If given a graph use figures/specific examples
2. Mention where the graph levels off, that most of the enzyme substrate complexes have been formed by this point
   -again use figures if you are given a graph
3. For a temperature graph mention that the more kinetic energy = more successful collisions and complexes formed
4. On the rise of the graph mention that all other factors should be kept constant

Question 16

What is the lock and key model?

Answer 16

A model where the shape of the active site doesn’t change when a substrate binds to it

Question 17

What is the induced fit hypothesis?

Answer 17

A model where the tertiary structure of an enzyme changes as the substrate approaches so the active site then moulds around the substrate

Question 18

What is the active site like in the induced fit hypothesis?

Answer 18

The active site is not complimentary to the substrate the start, the active site then becomes complimentary after wrapping around the substrate

Question 19

Exam technique on the induced fit hypothesis

Answer 19

1. Shape of active site isn’t complimentary/shape of the active site is flexible
2. The active site changes shape to bind with substrate and form an enzyme substrate complex

Question 20

What are the similarities between the lock and key model and the induced fit hypothesis

Answer 20

-Both have active sites
-Both have a distinctive shape and arrangement

Question 21

What are the differences between the lock and key model and the induced fit hypothesis?

Answer 21

-In the lock and key model the substrate is only specific to one active site
-In the induced fit hypothesis the enzyme isn’t a simple, rigid shape like it is in the lock and key model
-The shape of the active site is flexible in the induced fit hypothesis
-In the induced fit hypothesis the active site is not fully complimentary to the substrate

Question 22

What is an inhibitor?

Answer 22

Something that restricts/prevents an action or process

Question 23

What is a competitive inhibitor?

Answer 23

An inhibitor (molecule) that binds to the active site due to it having a similar shape as the substrate

Question 24

What does a competitive inhibitor do?

Answer 24

1. The inhibitor competes with the substrate for the active site
2. The inhibitor fills the active site due to its similar shape
3. The substrate now can’t bind to the active site
4. No enzyme substrate complex is formed causing a lower rate of reaction

Question 25

Exam technique on competitive inhibitors

Answer 25

1. Talk about how the inhibitor fills/blocks the active site of an enzyme
2. Mention that the inhibitor is complimentary/similar to the active site
3. The inhibitor competes with the substrate/there is competition between the inhibitor and the substrate
4. Overall, this prevents an enzyme substrate complex to be formed

Question 26

What is a non-competitive inhibitor?

Answer 26

The inhibitor (molecule) binds to the allosteric site of an enzyme and alters the shape of the active site and the substrate can no longer bind

Question 27

What does a non-competitive inhibitor do?

Answer 27

1. The inhibitor binds to an allosteric site
2. This alters the shape of the enzyme including the active site
3. This means the substrate can no longer bind to the active site
4. No enzyme substrate complex can be formed causing a lower rate of reaction

Question 28

Exam technique on a non-competitive inhibitor

Answer 28

1. Talk about how the inhibitor binds at an allosteric site rather than the active site
2. Explain how binding at the allosteric site affects the shape of the active site
3. This therefore prevents a substrate binding to the active site as their complimentary shapes now differ, this restricts an enzyme substrate complex being formed

Question 29

Exam technique on urea affecting enzymes

Answer 29

1. What is urea? - the main component of urine and is produced when proteins break down into ammonia
2. Mention that it is a toxic substance - the body therefore wants to get rid of it
   3.Urea is a non-competitive inhibitor on enzymes - define what this means
3. Why is it an inhibitor - breaks down hydrogen bonds, this changes the structure of the enzyme
4. No enzyme substrate complex can be formed as the enzyme has changed shape (including the complimentary active site)
5. Urea overall decreases enzyme activity