C1.1 Enzymes and Metabolism

Question 1

What are enzymes?

Answer 1

Globular proteins that acts as biological catalysts that speed up chemical reactions in the body.
They can be recycled as they are never “used up” in reactions

Question 2

What is metabolism? What is the role of enzymes in metabolism?

Answer 2

Metabolism is the sum of all chemical reactions occuring in an organism.
- enzymes control metabolism
- lower activation energy of reactions
- provide alternative pathways
- increase the collisions
- occur when substrates are dissolved in water
- enzyme can move if in fluid

Question 3

Anabolic and catabolic reactions

Question 4

Enzymes as globular proteins with an active site for catalysis

Question 5

How do enzymes work? What is the name of this model?

Answer 5

• Enzymes are specific to substrates (reactants)
• Enzymes have active sites that are specific to the substrate (match physically and chemically)

The Induced Fit Model:
- As substrate binds to enzyme to form enzyme substrate complex, the active site changes slightly
- enhances catalytic activity
- enzyme returns to previous shape after reaction

Question 6

What happens to the active site of an enzyme when it undergoes denaturation?

Answer 6

The active site becomes distorted and loses its substrate specificity.
It is unable to catalyse reactions and this is usually irreversible

Question 7

What is enzyme immobilization? What is the point of it?

Answer 7

It is when the enzymes are unable to move and so they stay in one place after reactions.
Used commercially so the enzyme doesn’t have to be removed from the product.

Question 8

What is most necessary for a substrate molecule and an enzyme’s active site to come together?

Answer 8

Movement and collision of the enzyme and substrate.

Question 9

What happens to enzymes when you increase the amount of substrate?

Answer 9

An increase in enzyme activity until the point of saturation where they work at their maximum rate and plateau after that.

Question 10

What is the overall metabolic activity controlled by?

Answer 10

• rate of enzyme production and breakdown
• inhibitors
• enzyme interaction with products

Question 11

What are metabolic pathways? What are the types of pathways?

Answer 11

Pathways are a series of reactions from a starter molecule/precursor to an end product.
Each reaction is catalyzed by a different enzyme.
Cyclical pathways:
The reactant becomes the product

Non-cyclical/linear:
reactant is different from the product

Question 12

What are anabolic reactions?

Answer 12

Reactions that build up a product
- condensation reactions
- photosynthesis

Question 13

What are catabolic reactions?

Answer 13

Reactions that break down a product
- hydrolysis
- cell respiration

Question 14

What are intracellular and extracellular metabolic reactions?

Answer 14

Intracellular:
- occur in the cell
- e.g: DNA replication, cellular respiration

Extracellular:
- occur outside the cell
- e.g: digestive enzymes in the intestines

Question 15

What is the efficiency of metabolic reactions?

Answer 15

They are not 100% efficient:
- energy is released as heat
(especially in respiration)

Question 16

What are endotherms and ectotherms?

Answer 16

Endotherms:
warm blooded
control their own body temp

Ectotherms:
cold blooded
rely on external sources for heat

Question 17

What is denaturation?

Answer 17

The permanent or temporary change in 3D shape and protein structure due to the breaking of bonds.
Causes a change in active site and inability to catalyze reactions.

Question 18

What factors change rate of enzyme activity?

Answer 18

• Temperature
• pH
• Substrate/enzyme concentration

Question 19

How does pH affect enzymes?

Answer 19

Outside of optimum pH, enzymes denature if pH is too far from ideal.

Question 20

How does temperature affect enzymes?

Answer 20

Activity increases as temp increases until optimum is reached. After optimum enzymes denature due to breaking of bonds.

Question 21

How does concentration of enzymes/substrate affect their activity?

Answer 21

Higher concentration increases activity up until a maximum when it plateaus.

Question 22

What are inhibitors? What types of inhibition are there?

Answer 22

Substances that prevent or reduce enzyme activity.
- Competitive inhibition
- Non-competitive inhibition
- Feedback inhibition
- Mechanism based inhibition

Question 23

What is competitive inhibiton?

Answer 23

When a substance competes with a substrate for the active site, as they are chemically similar.
The inhibitor binds to the active site, blocking substrates from binding.
The rate will slow down but will eventually reach the same point.
Higher inhibition rate decreases the rate of reaction but the same amount of enzymes are still available.
They can be outcompeted if there are more substrates.
E.g: statins (lower cholesterol)

Question 24

What is non-competitive inhibition?

Answer 24

WHen a substance binds to the allosteric site of an enzyme (not the active site).
This changes its shape and stops the enzyme from functioning.
This is reversible.

Question 25

What is feedback inhibition?

Answer 25

When the inhibitor is produced in a metabolic pathway.
The product becomes an inhibitor of the first enzyme in the pathway.
Used to stop the cell from making unnecessary products and conserve energy.
This acts as a non-competitive inhibitor.
E.g: Isoleucine

Question 26

What is mechanism based inhibition?

Answer 26

When a substrate analogue (molecule) forms covalent bonds with the active site.
This is an irreversible inhibition.
The substrate analogue is changed by the enzyme after bonding and forms a stable inhibitor-enzyme complex.
e.g: Penicillin

Question 27

Explain how penicillin is a mechanism based inhibitor:

Answer 27

Penicillin is an antiobiotic that kills bacteria by binding with the enzymes that form links in bacterial cell walls.
By forming a stable inhibitor-enzyme complex, the cell walls burst from the pressure as they are not linked together.
They do not affect us as we do not have cell walls.

Question 28

Explain antibiotic resistance:

Answer 28

DNA mutations can change the shape of an enzyme’s active site.
If bacteria aren’t completely killed off, the bacteria can mutate and pass on plasmid DNA through conjugation.
This renders penicillin ineffective in inhibiting the enzymes.
Resistance can happen when antibiotic rounds are not completed.

Question 29

What is substrate specificity?

Answer 29

Enzymes are specific to the substrates they bind to