2.1 Metabolic Pathways

Question 1

What is Metabolism?

Answer 1

Metabolism is the biochemical process that life depends on
Metabolic pathways are controlled by enzymes

Question 2

Identify 3 features of metabolic pathways

Answer 2

Reversible steps
Irreversible steps
Alternative routes

Question 3

In what 2 ways can metabolic reactions be classified as?

Answer 3

Catabolic and Anabolic

Question 4

What is a catabolic reaction?

Answer 4

The breakdown of large molecules into smaller ones releasing energy

Question 5

What is an anabolic reaction?

Answer 5

The build up of large molecules from smaller ones requiring energy

Question 6

What 2 compounds make up a membrane?

Answer 6

Proteins and Phospholipids

Question 7

How do molecules travel through protein pores in the membrane?

Answer 7

Via diffusion

Question 8

How do molecules travel though protein pumps in the membrane?

Answer 8

Via active transport

Question 9

What is activation energy (Ea)?

Answer 9

An initial input of energy that all reactions need

Question 10

What 2 ways can enzymes help to lower activation energy (Ea)?

Answer 10

Affinity for substrate
Substrate orientation

Question 11

Describe ‘Induced Fit’

Answer 11

There is a high affinity between substrate and enzyme
The active site is flexible and slightly alters its shape when the substrate binds
The close fit ensures the active site is in close contact with the substrate

Question 12

What does the word affinity mean?

Answer 12

The chemical draw between enzyme and substrate/end product
Can be high (s) or low (ep)

Question 13

What has a high affinity for the enzymes active site?

Answer 13

Substrate

Question 14

What has a low affinity for the enzymes active site?

Answer 14

The end products in a reaction

Question 15

What limits the rate of a reaction at low substrate concentrations?

Answer 15

Substrate availability

Question 16

What limits the rate of a reaction at high substrate concentrations?

Answer 16

Enzyme availability

Question 17

How does a competitive inhibitor inhibit the rate of an enzyme controlled reaction?

Answer 17

It is also complementary to the enzymes active site and competes with the substrate. If it binds it prevents the reaction from taking place

Question 18

What effect will a competitive inhibitor have in a reaction with a low concentration of substrate?

Answer 18

The rate of reaction is lowered.
The number of successful collisions that the enzyme has with the substrate is less frequent since the enzymes active site may be occupied by a competitive inhibitor.

Question 19

What effect will a competitive inhibitor have in a reaction with a high concentration of substrate?

Answer 19

At high substrate concentrations the substrate molecules are abundant enough to out compete the competitive inhibitors. More successful collisions occur.

Question 20

What effect does a non-competitive inhibitor have on an enzyme?

Answer 20

When a non-competitive inhibitor binds the enzymes allosteric site, the active site changes shape and is no longer complementary to the substrate and so it wont fit.

Question 21

Where does a non-competitive inhibitor bind to on an enzyme?

Answer 21

The allosteric site

Question 22

What effect does a non competitive inhibitor have on the rate of a reaction?

Answer 22

The maximum reaction rate is lowered, regardless of how much substrate is added. The active site has changed and enzyme concentration is reduced.

Question 23

What inhibits enzyme action in feedback inhibition?

Answer 23

The end product of an enzyme catalysed reaction binding to an enzyme in the pathway.

Question 24

Give two advantages of feedback inhibition in a metabolic pathway.

Answer 24

• Regulates the whole pathway.
• Prevents wasteful conversion and accumulation.