Metabolic Pathways

Question 1

What is a metabolic pathway?

Answer 1

A series of enzyme-controlled reactions.

Question 2

What does metabolism describe?

Answer 2

All the reactions taking place within a cell.

Question 3

What are the two types of metabolic reactions?

Answer 3

Anabolic and catabolic

Question 4

What is an anabolic reaction?

Answer 4

Build up complex molecules from simple building blocks.

Question 5

What is a catabolic reaction?

Answer 5

Break down complex molecules into simple building blocks.

Question 6

Do anabolic reactions require energy?

Answer 6

Yes

Question 7

What is an example of an anabolic reaction?

Answer 7

Protein synthesis - amino acids are built up into proteins.

Question 8

Do catabolic reactions require energy?

Answer 8

No - they release energy.

Question 9

What is an example of a catabolic reaction?

Answer 9

Aerobic respiration - glucose and oxygen are broken down into carbon dioxide and water.

Question 10

Give an example of how closely linked metabolic pathways are?

Answer 10

The energy generated by aerobic respiration (catabolic) is used for protein synthesis (anabolic).

Question 11

How are metabolic pathways regulated?

Answer 11

By enzymes.

Question 12

Can metabolic pathways be reversible?

Answer 12

They can be reversible, irreversible, or use an alternative route.

Question 13

Give an example of a reversible metabolic pathway.

Answer 13

Fermentation in animals - when oxygen is present in lactate can be reversed back into pyruvate.

Question 14

Give an example of an irreversible reaction.

Answer 14

Fermentation in plants and yeast.

Question 15

What is the purpose of the cell membrane?

Answer 15

• It controls the flow of materials into and out of the cell.
• They also form the surfaces and areas where metabolic reactions can occur.

Question 16

What are common examples of membrane-bound organelles?

Answer 16

Mitochondria and chloroplasts

Question 17

What are the purposes of mitochondria and chloroplasts in terms of metabolic pathways?

Answer 17

They form compartments that keep metabolites close together or separated.

Question 18

How many membranes do the mitochondria have?

Answer 18

It has a double membrane - inner and outer.

Question 19

Describe the inner membrane of the mitochondria.

Answer 19

It is folded to localise metabolic activity.

Question 20

Where is ATP found in plants?

Answer 20

In chloroplasts.

Question 21

What are the advantages of compartmentalised membranes?

Answer 21

Allows a high surface to volume ratio which allows high concentrations of substrates inside - leading to high reaction rates.

Question 22

What is the cell membrane made up of?

Answer 22

• proteins

- phospholipids (type of fat)

Question 23

What is the benefit of the phospholipid layer in the cell membrane?

Answer 23

The bi-layer gives the membrane a fluid nature, making it flexible.

Question 24

What are the three main forms of proteins embedded in the cell membrane?

Answer 24

• pores
• pumps
• enzymes

Question 25

What is the function of pores in the cell membrane?

Answer 25

Allows diffusion of specific molecules - larger molecules - across the membrane, through a channel.

Question 26

What is the function of pores in the cell membrane?

Answer 26

Act as carrier molecules to transfer specific ions against the concentration gradient - this is active transport and requires ATP.

Question 27

What is the function of enzymes in the cell membrane?

Answer 27

Speeds up the rate of biochemical reaction in the cell.

Question 28

What are enzymes?

Answer 28

Biological catalysts made up of protein, that speed up the rate of reaction.

Question 29

What controls the rate of a metabolic pathway?

Answer 29

Enzymes

Question 30

What is the activation energy?

Answer 30

The energy required to start the reaction.

Question 31

How do enzymes affect the activation energy of a reaction?

Answer 31

They lower the activation energy.

Question 32

Is the active site a rigid structure?

Answer 32

No, it's flexible.

Question 33

What does 'induced fit' mean?

Answer 33

When the substrate enters the active site, they both change slightly to make the active site fit closely to the substrate molecule.

Question 34

Why is the induced fit useful?

Answer 34

- ensures close contact between the active site and the substrate molecules - increases the chance of a reaction.

Question 35

What is the affinity of a molecule?

Answer 35

The tendency for it to bind to an enzyme.

Question 36

Describe the affinity in terms of a reaction.

Answer 36

Substrates have a high affinity for the active site, whereas products have a lower affinity for the active site and therefore separate.

Question 37

What is an inhibitor of a metabolic pathway?

Answer 37

A substance that decreases the rate.

Question 38

What are the three kinds of inhibitors of a metabolic reaction?

Answer 38

- competitive - non-competitive - feedback

Question 39

How do competitive inhibitors work?

Answer 39

They have a similar shape to the substrate and are able to compete for the active site. They can bind to the active site and block substrates - reducing the reaction rate.

Question 40

How do you overcome competitive inhibition?

Answer 40

Increase substrate concentration

Question 41

How do non-competitive inhibitors work?

Answer 41

It binds to another part of the enzyme (not the active site), permanently changing the shape of the enzyme and active site, preventing the substrate from binding, and decreasing the rate.

Question 42

How do you overcome non-competitive inhibitors?

Answer 42

No way to reverse the effect.

Question 43

How does feedback inhibition work?

Answer 43

As the concentration of the end product builds up, some of it binds to the enzyme which slows down the reaction.