2.1 b Control of metabolic pathways

Question 1

What is activation energy?

Answer 1

the energy required to initiate a reaction is called its activation energy. It is the energy barrier substrates must overcome before they become products.

Question 2

What are catalysts?

Answer 2

catalysts speed up the rate of chemical reactions by lowering the activation energy required for the reactions to proceed.

Question 3

What are enzymes?

Answer 3

Enzymes are biological catalysts

Question 4

Why is the presence of enzymes very important?

Answer 4

at normal body temp, chemical reactions would take place at too slow a rate to maintain life if enzymes were not present

Question 5

What is the function of the enzyme?

Answer 5

Enzymes therefore act by reducing the activation energy for a reaction to occur faster at the lower temp found in living cells

Question 6

What is the structure of an enzyme?

Answer 6

Enzymes are three dimensional globular protein molecules that are sensitive to both pH and temperature.

The specific part of the enzyme molecule that connects with a substrate molecule is called the active site

The shape of the active site on an enzyme molecule is specific to only one substrate

Question 7

What determines the sequence of amino acids in the enzyme?

Answer 7

The sequence of bases in the DNA coding for the enzyme

Question 8

What determines the shape of the active site?

Answer 8

The sequence of amino acids in the enzyme

Question 9

If the shape of a substrate molecule is complementary to the active site of the enzyme it will have what?

Answer 9

high affinity for the active site

Question 10

When will it have a low affinity?

Answer 10

Products of enzyme substrate reactions have a low affinity for the active site of the enzyme.

Question 11

What is induced fit?

Answer 11

the active site begins in an open position which allows the substrate to move in and bind.
binding of the substrate causes a change in the shape of the active site to be a closed position.
This brings the substrate and enzyme closer together, increasing the chance of a reaction
Once the product has formed the shape of the active site returns to the open position and the product moves out.

Question 12

What is a synthesis reaction?

Answer 12

enzyme joins two molecules together to make the product

Question 13

What is a degradation reaction?

Answer 13

enzyme breaks down a large substrate molecules into smaller product molecule

Question 14

Advantage of a multi enzyme complex to the cell?

Answer 14

able to catalyse faster reactions and control order of reactions

Question 15

how can you control the rate of enzyme reactions?

Answer 15

substrate concentration
enzyme concentration
end product inhibition
competitive and non competitive inhibitors

Question 16

what happens as the substrate concentration increases?

Answer 16

the rate of reaction increases and then becomes constant

Question 17

diagram// when the slope is increasing?

Answer 17

as substrate concentration increases more substrate molecules are able to bind with enzyme active site and the rate of reaction increases.

Question 18

when the diagram platues?

Answer 18

the substrate concentration is high enough that all the active sites are filled. increasing the substrate concentration has no further effect on the rate of reaction which remains constant. enzyme concentration is now the limiting factor

Question 19

what will further increase the rate of this reaction?

Answer 19

enzyme concentration will need to be increased

Question 20

What are the three types of inhibitor molecules?

Answer 20

• end product inhibitor (feedback inhibitor)
• competitive inhibitor
• non competitive inhibitor

Question 21

Explain Feedback Inhibition?

Answer 21

In feedback inhibition the end product binds to an early enzyme in the metabolic pathway altering the shape of the enzyme’s active site and blocking the pathway.
This prevents too much end product from being produced
As the concentration of the end product drops inhibition ceases and the pathway resumes again

Question 22

Explain Competitive Inhibition?

Answer 22

Competitive inhibitor molecules have a shape similar to that of the substrate.
They bind with the enzyme’s active site preventing the substrate from entering
Because the substrate and inhibitor are in competition for the active site increasing the substrate concentration cause an increase in the rate of reaction

Question 23

Explain non competitive inhibition?

Answer 23

Non competitive inhibitors bind to the part of the enzyme that is not its active site (allosteric site)
As a result the shape of the active site is altered and the substrate cannot enter
Because the inhibitor and substrate are not in competition for the active site increasing substrate concentration has no effect on the rate of reaction
The rate of reaction remains low

Question 24

Is competitive or non competitive reversible or irreversible?

Answer 24

Competitive inhibition is reversible

Non Competitive inhibition is irreversible

Question 25

Examples of non competitive inhibition?

Answer 25

Poisons such as arsenic and heavy metals such as lead and mercury are non competitive inhibitors they act by attaching to the allosteric site of the enzyme and changing the structure of the enzyme
The active site changes shape and its unable to connect with the substrate molecule

Question 26

TOP TIP example of non competitive inhibitor?

Answer 26

cyanide is a non competitive inhibitor that inhibits the enzymes of aerobic respiration

Question 27

What occurs at the allosteric site of an enzyme?

Answer 27

non competitive inhibitor to enzyme

Question 28

In what way does end product inhibition benefit a cell?

Answer 28

control - prevents too much end product being produced

Question 29

What is each step within a metabolic pathway controlled by?

Answer 29

by one specific enzyme coded for by one specific gene

Question 30

When is the pathway said to be blocked?

Answer 30

If an enzyme within the pathway is missing or does not work properly due to a mutation the pathway is blocked

Question 31

When are enzymes always switched on?

Answer 31

Some metabolic pathways are required continuously and the genes that code for their enzymes are always switched on

Question 32

When are enzymes switched off?

Answer 32

other pathways are only needed on certain occasions
to prevent resources being wasted, the genes that code for the enzymes in the pathways are switched on or off as required in response to signals from within the cell from its environment

Question 33

Explain the Jacob Monod Theory?

Answer 33

E coli can break down lactose sugar into glucose and galactose by producing the enzyme B-galactosidase
The bacterial cells then use the glucose for cell respiration
The enzyme is only produced when lactose is present
this prevents wastage of valuable cell resources such as ATP and amino acids

Question 34

What does it mean when genes are switched on?

Answer 34

If genes are switched on (expressed) it is actively coding for the enzyme and the enzyme is produced

Question 35

What does it mean when genes are switched off?

Answer 35

they are not expressed they do not actively code for the enzyme and is not produced

Question 36

TOP TIP Jacob monod theory can be used as an example of what?

Answer 36

Genetic control of a metabolic pathway

Question 37

Explain Enzyme Induction?

Answer 37

The gene coding for the enzyme B-galactosidase is expressed only when lactose is present
This is called enzyme induction
Lactose is the inducer - its presence in the environment signals the gene to be expressed and the enzyme to be produced

Question 38

Explain Gene action in bacteria jacob monod theory (lactose absent)?

Answer 38

Regulator gene is always on causing the repressor molecule to be produced
Repressor molecule (protein) combines with the operator gene
Repressor molecule switches off the operator gene
Operator gene is unable to function therefore the structural gene remains off
Enzyme is not produced

Question 39

Explain Gene action in bacteria jacob monod theory (lactose present)?

Answer 39

Regulator gene is always on causing the repressor molecule to be produced
repressor molecule combines with lactose
repressor lactose complex is unable to switch off the operator gene
Operator gene switches on structural gene
enzyme is produced
enzyme breaks down lactose
when all lactose has been broken down the repressor molecule is again free to switch off operator and enzyme production stops
Lactose acts as the inducer molecule

Question 40

What is Lac operon?

Answer 40

signal molecule is lactose as it combines with the repressor molecule resulting in the structural gene being expressed and B-galactosidase being produced

Question 41

Describe the role of genes in control of the metabolic pathways?

Answer 41

each step within a metabolic pathway is controlled by one specific enzyme coded for one specific gene
Order of bases in gene determines order of amino acid which determines the shape, structure and function