Metabolic Pathways and their Control 2.1

Question 1

What is Cell Metabolism?

Answer 1

Thousands of enzyme controlled reactions that occur within a living cell

Question 2

What are Metabolic Pathways?

Answer 2

It is the sequence of reactions, controlled by enzymes that change one metabolite into another

Question 3

What do catabolic pathways do?

Answer 3

Catabolic pathways bring about the breakdown of complex molecules to simpler ones usually releasing energy and often providing building blocks
e.g. Protein -> Amino Acids

Question 4

Do anabolic and catabolic pathways depend on eachother?

Answer 4

Yes, they are closely integrated and depend on eachother

Question 5

What do anabolic pathways do?

Answer 5

Anabolic pathways bring about the build up of large molecules from small molecules. This requires energy.
e.g. Amino acids -> proteins

Question 6

What form is the energy in?

Answer 6

ATP

Question 7

What are metabolic pathways controlled by?

Answer 7

They are controlled by enzymes and each enzyme catalyses a specific reaction.

Question 8

Is there only one pathway per reaction?

Answer 8

No, pathways include alternative routes. Pathways may also have reversible and irriversible steps.

Question 9

What can the plasma membranes structure be described as?

Answer 9

It is selectively permeable
It is made up of a bilayer of proteins which are in constant motion
Proteins are scattered on the surface and embedded within the membrane.
The fluid mosaic model.

Question 10

What are the roles of the Membrane Proteins?

Answer 10

The proteins on the surface act as enzymes and are involved in cell communication.
Many proteins which span the membrane system as a whole are essential for intracellular and intercellular transport

Question 11

What do Protein Pores do in transport?

Answer 11

Only allow specific substances to passively move across the membrane (diffusion)

Question 12

What to Protein pumps do in transport?

Answer 12

Active transport requires ions or molecules to be pumped against the concentration gradient. Energy released from the breakdown of ATP is needed to change the shape of the protein and allow the molecules or ions to transfer across the membrane.

Question 13

What does the sodium-potassium pump do?

Answer 13

Actively pumps sodium ions out of the cell and potassium ions into the cell both against the concentration gradient.

Question 14

What factors affect how quickly a protein pump can operate?

Answer 14

Temperature and availability of oxygen and glucose affect the rate of respiration and therefore the rate of active transport (since this requires ATP)

(anything that effects the rate of respiration effects the rate of active transport)

Question 15

Enzymes in the membrane

Answer 15

Some proteins in the membrane are enzymes which catalyse steps within cellular metabolic processes e.g ATP synthase

Question 16

Why enzymes?

Answer 16

Energy is required to start a reaction to initially break bonds and this is known as the activation energy

Question 17

What is the transition state?

Answer 17

When the bonds in a reaction have broken and are unstable.

Question 18

What does the enzyme do to the activation energy?

Answer 18

It lowers the activation energy so that the reaction can occur at lower temperatures.

Question 19

What does the enzyme do to substrates?

Answer 19

It brings the substrates closer together to allow a reaction to happen

Question 20

What is the induced fit model?

Answer 20

The shape of the active site alters slightly to better fit the substrate - initially the shapes are only complementary not an exact fit

Question 21

Explain the affinity relationships.

Answer 21

Substrates have a high affinity for the active site.

Products have a ow affinity for the active site.

Question 22

What is affinity?

Answer 22

A chemical attraction

Question 23

What do active sites do to help a reaction and how? (Clue: starts with o)

Answer 23

When two or more substrates are involved in the reaction the shape change of the active site helps orientate the substrate for the reaction to occur

Question 24

How can we track enzyme activity?

Answer 24

It can be measured by either the decrease in the substrates or the increase in the products;

• Gas Production
• Changes in pH
• Colour Changes

Question 25

How is the rate of an enzyme-controlled reaction affected?

Answer 25

It is affected by pH, temperature, the concentration of substrate and products and the availability of enzyme active sites

Question 26

How is enzyme activity regulated?

Answer 26

• Controlling the number of enzyme molecules in a cell
• Keeping reactants in compartments
• Driving the reaction in different directions using reversible steps triggered by the presence of a substrate or removal of a product (like equilibrium)
• Controlling enzyme activity through inhibition

Question 27

What do enzyme inhibitors do?

Answer 27

They reduce the rate of an enzyme catalysed reaction by interfering with the enzyme in some way - can be permanent or temporary

Question 28

What is Competitive Inhibition

Answer 28

Competitive inhibitors bind at the active site but remain unreacted since they have a different structure from the substrate, preventing the substrate from binding

Question 29

Is the competitive Inhibition permanent?

Answer 29

No, it is USUALLY temporary and can be reversed by increasing the substrate concentration

Question 30

What is Non-competitive inhibition?

Answer 30

Non-competitive inhibitors bind to the enzyme but not in the active site. When the inhibitor binds it causes a change in the shape of the active site.

Question 31

Is non-competitive inhibition temporary?

Answer 31

It may or may not be reversible. Since they do not compete with substrate molecules increasing substrate concentration does NOT reverse this, it will have no effect

Question 32

What is Feedback Inhibition?

Answer 32

Also known as end-product inhibition as often the final product itself acts as inhibitor.
It binds to an almost Eric site of an earlier enzyme leering the shape of the active site and inhibiting this enzyme. This blocks the pathway and prevents further synthesis of end product

Question 33

What does it mean; Multi-enzyme complexes?

Answer 33

As enzymes are often part of a multi step pathway they are often found in groups or as multi-enzyme complexes