2A -

Question 1

What is a metabolic pathway?

Answer 1

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

Metabolic pathways can have reversible and irreversible steps and alternative routes.

Question 2

What are the functions of proteins in a membrane?

Answer 2

Proteins embedded in phospholipid membranes have roles as pores, pumps and enzymes.

Question 3

What is the function of membranesaround organelles within a cell. Eg nuclear membrane, mitochondrial membrane, chloroplast membrane?

Answer 3

Membranes form compartments to localise metabolic pathways in the cell.

Question 4

What is the purpose of localising metabolic pathways in the cell through membranes?

Answer 4

-makes the metabolic pathway easier to control

Question 5

Functions of pores in a membrane?

Answer 5

Pores: allow materials to diffuse passively through the membrane

Question 6

Functions of pumps in a membrane?

Answer 6

Pumps: use energy for active transport to move material against the concentration gradient

Question 7

Functions of enzymes in a membrane?

Answer 7

Enzymes: carry out reactions and have active site exposed to one side of the membrane

Question 8

How does the substrate concentration effect rate of an enzyme reaction?

Answer 8

Increasing the substrate concentrationmeans more enzyme-substrate complexes can form so speeds upthe rate of a reaction. Eventually the rate will level offwhen a maximum rate for the concentration of enzyme is reached.

Question 9

How can some metabolic reactions be reversible?

Answer 9

Some metabolic reactions are reversible. The presence of a substrateor the removal of a productwill drive a sequence of reactions in a particular direction.

Question 10

How do competitive inhibitorsaffect enzyme activity?

Answer 10

Competitive inhibitorsbind at the active site preventing the substrate from binding. Competitive inhibition can be reversed by increasing substrate concentration.

Question 11

How do non-competitive inhibitorsaffect enzyme activity?

Answer 11

Non-competitive inhibitorsbind away from the active site but change the shape of the active site preventing the substrate from binding. Non-competitive inhibition cannot be reversed by increasing substrate concentration.

Question 12

What is an anabolic reaction?

Answer 12

Reactions within pathways can be anabolic or catabolic.

Anabolic reactionsbuild up large molecules from small molecules(biosynthetic) and require energy.

Question 13

What is a catabolic reaction?

Answer 13

Reactions within pathways can be anabolic or catabolic.

Catabolic reactions break down large molecules into smaller molecules(degradative) and release energy.

Question 14

Explain the Induced Fit Hypothesis of enzyme action.

Answer 14

According to the Induced fit hypothesis the active site of an enzyme reduces (lowers) the activation energy and affects the affinity of the substrate and products for the active site.

· Induced fit occurs when theactive site changes shape to better fit the substrate after the substrate binds.

· The substrate molecule(s)have a high affinity for the active siteand the subsequentproducts have a low affinity allowing them to leave the active site.

Question 15

What other ways can the rate of a pathway be controlled other than by substrate/product concentration?

Answer 15

Pathways can be regulated by the presence or absence of particular enzymesor by regulation of the rates of reaction of key enzymes.

Three ways to control metabolic pathways include: through competitive, non-competitive and feedback inhibition of enzymes.

Question 16

How does Feedback Inhibition work?

Answer 16

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

The end-product then inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end-product.

Question 17

Define metabolism

Answer 17

• all the biochemical reactions in a cell

- enzymes catalyse these biochemical reactions

Question 18

What is the purpose of controlling metabolic pathways?

Answer 18

-controlling the rate and direction of pathways ensures the cell makes the right amounts of what it needs to make

Question 19

What is the purpose of integrating metabolic pathways?

Answer 19

integration allows the cell to divert resources to other pathways that need them eg. lipids join the energy pay-off phase of glycolysis

Question 20

What is the purpose of alternative routes in metabolic pathways?

Answer 20

-materials can be diverted to alternative routes to allow control of what is produced or used by metabolism

Question 21

Some enzymes are reversible - when does reversing happen?

Answer 21

-reversing happens when concentrations of substrate concentration is low and product concentration is high

Question 22

What is the importance of reversible enzymes?

Answer 22

-allow metabolic pathways to be redirected so metabolism makes the products that the cell needs

Question 23

What does the effect of increasing the substrate concentration have?

Answer 23

Increases the rate of reaction

Question 24

What does the effect of decreasing the substrate concentration have?

Answer 24

Reduces the rate of reaction