2.1 Metabolic Pathways and their control

Question 1

Define ‘metabolism of a cell’

Answer 1

Sum total of all biochemical reactions that occur within a cell

Question 2

Define a metabolic pathway?

Answer 2

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

Question 3

What are the three types of steps in a metabolic pathway?

Answer 3

Reversible
Irreversible
Alternative

Question 4

What is an advantage of having reversible steps in a metabolic pathway?

Answer 4

Allows processes to be kept under precise control

Question 5

What is an advantage to having alternative steps in a metabolic pathway?

Answer 5

Allows an end product still to be reached if a specific enzyme / substrate is unavailable

Question 6

Describe an ‘Anabolic’ pathway

Answer 6

Anabolic

• Synthesis/Build up of a larger molecule from smaller molecules
• Requires Energy

Question 7

Give an example of an anabolic process

Answer 7

Photosynthesis

Question 8

Describe a ‘Catabolic’ pathway

Answer 8

• Break down of larger molecules into smaller molecules

- Releases Energy

Question 9

Give an example of a catabolic process

Answer 9

Aerobic Respiration

Question 10

Describe the function of a cell membrane?

Answer 10

Controls the entry and exit of materials in a cell

Question 11

What are the inner folds of a membrane called?

Answer 11

Cristae

Question 12

What are the types of proteins found in a cell membrane?

Answer 12

• Protein Pump
• Channel forming protein
• Enzyme

Question 13

Metabolic pathways are controlled by the … and the regulation of …

Answer 13

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

Question 14

What is the ‘activation energy’

Answer 14

The minimum energy required to initiate a chemical reaction

Question 15

How do enzymes speed up the rate of a chemical reaction?

Answer 15

Speed up the reaction but are not used up because they lower the activation energy

Question 16

State the key characteristics of enzymes?

Answer 16

• Protein
• catalyses chemical reactions
• reduced activation energy of reaction
• converts substrate(s) to product(s)
• shape of substrate is complementary to shape of enzymes active site
• effected by temperature and/or pH

Question 17

Do substrates have high or low affinity for the active site of an enzyme?

Answer 17

High

Question 18

Do products have high or low affinity for the active site of an enzyme?

Answer 18

Low

Question 19

How does substrate concentration effect reversible reactions?

Answer 19

Reversible reactions can go either way depending on the relative concentrations of substrate/products

Question 20

Explain the process of ‘Induced Fit’

Answer 20

Induced fit is the process by which an enzyme molds its active site to fit more tightly around a substrate. It ensures the substrate is pulled in close and increases the chance of a reaction occurring.

Question 21

Name the three methods of enzyme inhibition of metabolic pathways?

Answer 21

• Competitive inhibition
• Non-competitive inhibition
• Feedback inhibition

Question 22

How does a competitive inhibitor work?

Answer 22

It has a similar shape to the substrate and so

competes with an enzyme’s substrate for binding to the active site.

Question 23

Competitive inhibition can be decreased by …

Answer 23

Competitive inhibition can be decreased by increasing substrate concentration, as more substrates mean there is more chance the substrate will bind instead of the inhibitor.

Question 24

A non-competitive inhibitor binds to an … on the enzyme and …

Answer 24

Non-competitive inhibitor binds to an allosteric site on the enzyme and changing the shape of the active site causing the enzyme to become denatured.

Question 25

Explain how non-competitive inhibition can be overcome?

Answer 25

Non-competitive inhibition cannot be reversed and increasing substrate concentration has no impact as the enzyme is denatured.

Question 26

Describe feedback inhibition

Answer 26

Feedback inhibition is when a build-up of a metabolic product inhibits the action of an enzyme earlier in the pathway, and this is an example of a self-regulating metabolic pathway.

Question 27

Explain the advantage of feedback inhibition?

Answer 27

Feedback inhibition prevents further synthesis of the metabolic product until the concentration of the metabolic has decreased. Saving energy.