Metabolic Pathways

Question 1

Define metabolism

Answer 1

All the (chemical) reactions which take place in a living cell.

Question 2

Define metabolic pathways.

Answer 2

Interconnected enzyme catalaysed biochemical reactions that take place within a living organism.

Question 3

Name the biosynthetic process involved in metabolic pathways

Answer 3

Anabolic

Question 4

State the degradation process involved in metabolic pathways

Answer 4

Catabolic

Question 5

What does anabolic pathways require?

Answer 5

An input of energy

Question 6

What do catabolic pathways do?

Answer 6

Breakdown molecules, releasing energy.

Question 7

Metabolic pathways can have what kind of steps?

Answer 7

Reversible and irreversible

Question 8

What do alternative routes allow?

Answer 8

Bypass steps in the metabolic pathway. Including irreversible steps.

Question 9

Explain alternative routes:

Answer 9

If a specific enzyme or substrate isn’t available in a pathway then sometimes an end product can still be made using an alternative route (another metabolic pathway)

Question 10

How can steps be reversible?

Answer 10

Enzymes catalyse reactions. Sometimes these reactions can work both ways. As the enzyme can act on the product to produce the original substrate.

Question 11

The membrane of some organelles are ……..

Answer 11

Highly folded

Question 12

What allows high concentrations of reactants and high reaction rates?

Answer 12

High surface area to volume ratio of small compartments

Question 13

Describe the shape of the membrane?

Answer 13

Fluid mosaic model

Question 14

What are embedded in the membrane?

Answer 14

Proteins, pumps, pores and enzymes

Question 15

What does the fluid mosaic model include?

Answer 15

Bi-layer, integral proteins, peripheral proteins

Question 16

What does channel proteins do?

Answer 16

Allow substances such as oxygen, carbon dioxide, water in and out of the cell.

Question 17

What does the peripheral protein do?

Answer 17

On membrane surface allows communication and is a receiver.

Question 18

Describe the function of protein pores

Answer 18

Protein pores allow certain molecules to pass through its pores by diffusion, this is a passive process that requires no energy.

Question 19

Describe the function of protein pumps

Answer 19

A protein pump actively transports ions across the cell membrane, this requires energy as transports ions against the concentration gradient.

Question 20

What do metabolic roles played by pores and pumps control?

Answer 20

This controls the presence and location of molecules required for metabolic pathways.

Question 21

What are metabolic pathways controlled by?

Answer 21

The presence or absence of particular enzymes and through the regulation of the rate of reaction of key enzymes within the pathway.

Question 22

Explain enzyme function in terms of the induced-fit model.

Answer 22

The active site changes shape to better fit the substrate.

Question 23

Explain the affinity of substrate molecules for the active site of an enzyme.

Answer 23

The substrate has a high affinity for the active site of the enzyme. Which means they want to bind.

Question 24

Describe the role of the active site in orientating reactants

Answer 24

The substrate molecules are orientated to ensure a transition state is formed and a reaction can proceed.

Question 25

Describe the role of the active site in the release of products with low affinity for the active site.

Answer 25

The products produced have a low affinity for the active site and are released.

Question 26

To function efficiently enzymes require?

Answer 26

Suitable temperatures
Appropriate pH
Adequate supply of substrate

Question 27

Describe the effect of a low substrate concentration.

Answer 27

At low substrate concentration the reaction rate is low- too few substrate molecules are present to make maximum use of all enzymes active sites.

Question 28

Describe the effect of a high substrate concentration.

Answer 28

Increase in substrate concentration results in an increase in the reaction rate, do more active sites become involved. The reaction can’t go any faster do all active sites become occupied.

Question 29

Describe the effects of substrate and end product on enzyme reaction.

Answer 29

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

Question 30

The presence of a substrate or the removal of a product will result in what?

Answer 30

Will drive a sequence of reactions in a particular direction.

Question 31

Competitive inhibitors:

Answer 31

• Binds to active site, preventing the substrate from doing so.
• Decreases rate of reaction being catalysed
• it can be reversed by increasing the concentration of the substrate

Question 32

Non-competitive inhibitors:

Answer 32

• binds away from the active site but alters the shape of the enzyme, indirectly changing the shape of the active site.
• the substrate can’t bind with the active site.
• can be used as a type of regulation as the number of affected enzyme molecules increases, the rate of reaction decreases.
• non-competitive inhibition can’t be reversed by increasing substrate concentration.

Question 33

Genes for some enzymes are?

Answer 33

Continuously expressed.

Question 34

Enzymes are always…

Answer 34

Enzymes are always present in the cell and they are controlled through the regulation of their rates of reaction.

Question 35

Feedback inhibition:

Answer 35

• occurs when end product in the metabolic pathway reaches a critical concentration
• the end-product then inhibits earlier enzyme, blocking the pathway, and so prevents further synthesis of the end-product.