Unit 1 - Metabolic Pathways Key Area 5

Question 1

What is Metabolism

Answer 1

Metabolism can be defined as all the chemical reactions that occur within the human body.

Question 2

What does Metabolic Pathways involve

Answer 2

Metabolic pathways involve the building up and breaking down of molecules.

Question 3

Are metabolic pathways reversible

Answer 3

Metabolic pathways can have reversible/irreversible steps, and alternative routes.

Question 4

How are metabolic reactions controlled

Answer 4

Metabolic pathways are controlled by the
presence or absence of particular enzymes
and the regulation of the rate of reaction of
key enzymes.

Question 5

What are the 2 types of reactions within metabolic pathways

Answer 5

Anabolic

Catabolic

Question 6

What is Anabolic

Answer 6

Anabolic reactions build up large molecules from small
molecules and require energy

e.g. building up of amino acids to form proteins

Question 7

What is catabolic

Answer 7

Catabolic reactions break down large molecules into
smaller molecules and release energy.

e.g. breaking down of glucose in glycolysis

Question 8

What is activation energy

Answer 8

Activation energy is the energy required to break chemical bonds in a reaction. It is the energy that is needed to allow the reaction to take place.

Question 9

What are metabolic pathways

Answer 9

Metabolic pathways are integrated and
controlled pathways of enzyme-catalysed
reactions within a cell.

Question 10

What is meant by the term affinity

Answer 10

The substrates show affinity (chemical attraction) for the active site.

After the reaction, the products have a low affinity for the active site and are released, leaving the enzyme free to repeat this process with new substrates

Question 11

How do reactants turn into products

Answer 11

Chemical bonds are broken when the reactants have gained enough energy to make them unstable, this is where they turn into products.

Question 12

How do enzymes speed up reactions

Answer 12

Enzymes speed up a chemical reaction by lowering the activation energy required for the reaction to take place.

Question 13

Describe Induced Fit

Answer 13

The active site of an enzyme is not a rigid structure. It is flexible and dynamic.

When a molecule of a substrate enters the active site, the shape of the enzyme’s active site change slightly, making the active site fit very closely round the substrate molecule – this is called induced fit

Induced fit ensures that the active site comes into very close contact with the molecules of substrate and increases the chance of the reaction taking place

Question 14

What do enzymes need to function efficiently

Answer 14

To function efficiently, an enzyme requires a suitable:

• Temperature
• pH
• Substrate concentration
• Product Concentration

Question 15

What are the effects of substrate and product
concentration on the direction and rate of
enzyme reactions

Answer 15

Some metabolic reactions are reversible and
the presence of a substrate or the removal of
a product will drive a sequence of reactions
in a particular direction.

Question 16

Explain the relationship between the rate of reaction and the substrate concentration in terms of the enzymes active site

Answer 16

1) At low substrate concentrations the reaction rate is slow because not all of the active sites are occupied by a substrate.
2) When the substrate concentration is increased the rate of the reaction increases as more active sites become occupied by a substrate.
3) At high substrate concentrations the reaction rate does not increase as there are no more active sites for the substrate to bind to.

Question 17

What is an inhibitor

Answer 17

An inhibitor is a substance that decreases the rate of an enzyme controlled reaction.

Question 18

What are the 3 types of inhibitors

Answer 18

There are three kinds of inhibition

• Competitive Inhibition
• Non competitive Inhibition
• Feedback Inhibition

Question 19

What is a competitive inhibitor

Answer 19

Competitive Inhibitor = competes with the substrate for the active site of an enzyme

Question 20

Describe how does a competitive inhibitor work
is it reversible
2 mark question usually

Answer 20

It has a similar molecular structure to the substrate, therefore can bind to the active site and block the substrate form binding, so the rate of the reaction decreases.
Competitive Inhibition can be reversed by increasing the substrate concentration. The substrate will eventually outnumber the competitive inhibitor.

Question 21

What is a non competitive inhibitor and how does it work

Answer 21

Does not have a similar molecular structure to the substrate and does not combine directly with the active site.

Attaches to a different area of the enzyme called a non-active (allosteric) site and changes the shape of the active site. This means that the substrate molecule no longer fits therefore preventing it from binding.

Non-competitive inhibition cannot be reversed by increasing substrate concentration

Question 22

When does feedback inhibition occur

Answer 22

Feedback inhibition occurs when the end-
product in the metabolic pathway reaches a
critical concentration

Question 23

Describe how a feedback inhibitor works

Answer 23

The end product binds to an enzyme that catalyses a reaction early in the pathway.
This binding blocks the pathway and prevents further synthesis of the product.

Feedback inhibition prevents waste of resources