2.1 - Metabolic Pathways

Question 1

Metabolism

Answer 1

The chemical reactions that occur in a cell that are necessary for life.

These chemical reactions are single steps in large closely integrated pathways that are controlled by enzymes.

Question 2

Reversible Steps

Answer 2

The pathway can go in both directions using the same enzyme.

Question 3

Irreversible Steps

Answer 3

The pathway can only go in one direction using an enzyme.

Question 4

Alternative Pathways

Answer 4

Metabolic pathways can have alternative routes. This can speed up the metabolic pathway.

Question 5

Catabolic Pathways

Answer 5

Catabolic reactions break down large molecules into smaller molecules.

This releases energy.

Question 6

Anabolic Pathways

Answer 6

Anabolic reactions build up large molecules from smaller molecules.

This requires energy.

Question 7

Membranes

Answer 7

Organelles that contain membranes include:
- Chloroplasts
- Mitochondria
- Cell membrane

Question 8

Protein Pores

Answer 8

Pores allow molecules and ions to pass across the membrane through passive transport (diffusion and osmosis)

Question 9

Protein Pumps

Answer 9

Pumps carry molecules and ions across the membrane through active transport.

Question 10

Role of Enzymes

Answer 10

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

Question 11

Enzymes: Active Site

Answer 11

The active site on an enzyme has a specific shape that is determined by the bonds between amino acids.

Question 12

Enzymes: Induced Fit

Answer 12

The active site changes its shape to better fit the substrate after the substrate binds.

Question 13

Affinity

Answer 13

The substrate molecule(s) have a high affinity for the active site. This pulls the substrates close to the active site.

The product(s) produced have a low affinity which allows them to leave the active site.

Question 14

Activation Energy

Answer 14

Induced fit lowers the activation energy required to start a metabolic reaction.

Question 15

Activation Energy (Ea)

Answer 15

The energy required to break or form bonds.

Enzymes lower the activation energy by bringing substrates of a reaction close together.

Question 16

Enzyme Reactions

Answer 16

Some metabolic reactions are reversible.

The presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction.

Question 17

Competitive Inhibitors

Answer 17

Competitive inhibitors bind at the active site which prevents the substrate from binding.

This can be reversed by increasing substrate concentration.

Question 18

Non-Competitive Inhibitors

Answer 18

Non-competitive inhibitors bind away from the active site but change the shape of the active site which prevents the substrate from binding.

This cannot be reversed by increasing substrate concentration.

Question 19

Feedback Inhibition

Answer 19

Feedback inhibition occurs when the end-product in the metabolic pathway reaches a critical (very high) concentration.

The end-product then inhibits an earlier enzyme, blocking the pathway, and so prevents more end-product being made.