Unit 1.6 - Metabolic Pathways

Question 1

What do enzymes lower?

Answer 1

The activation energy required for a chemical reaction to start

Question 2

Explain the induced fit model

Answer 2

• Substrates are chemically attracted to the active site they are said to have high affinity for it
• As the substrate starts to bind, the active site changes shape to fit it more closely
• This increases the rate of reaction
• When two or more substrates are involved the active site determines orientation of the reactants and holds them together in an induced fit
• This insures they are held in the correct way for the reaction to occur
• This process reduces the activation Energy needed by the reactants to reach the transitions state and allows the reaction to take place
• The subsequent products have a low affinity allowing them to leave the active site

Question 3

Explain the effect of substrate concentration on the rate of reaction?

Answer 3

When substrate concentration is low all active sites will not be occupied, the rate of reaction is slow
Increasing substrate concentration will increase rates of reaction as more active sites will be occupied
When all the active sites are occupied, the enzyme is saturated, this means increasing substrate concentration does not lead to an increase in reaction rate

Question 4

State the three types of enzyme inhibition?

Answer 4

Competitive inhibition, non-competitive inhibition and feedback inhibition

Question 5

Explain the mechanisms of competitive inhibition?

Answer 5

Competitive inhibitors find at the active site preventing the substrate from binding.
Competitive inhibitors can be reversed by increasing substrate concentration

Question 6

Explain the mechanisms of non-competitive inhibition

Answer 6

The inhibitors Bind away from the active site but change the shape of the active site is preventing the substrate from binding

This inhibition cannot be reversed by increasing substrate concentration

Question 7

Explain the mechanisms of feedback inhibition

Answer 7

It occurs when the end product in the metabolic pathway reaches a critical concentration

The end product then inhibits an earlier enzyme, blocking the pathway and so prevents further synthesis of the end product.

Question 8

What are metabolic pathways?

Answer 8

Integrated and controlled pathways of enzyme catalysed reactions within a cell

Question 9

What can metabolic pathways have?

Answer 9

Reversible steps, irreversible steps and alternative routes

Question 10

What is an anabolic pathway?

Answer 10

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

Question 11

What is a catabolic pathway?

Answer 11

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

Question 12

What are metabolic pathways controlled by?

Answer 12

The presence or a sense of particular enzymes and the regulation of the rate of reaction of key enzymes