Enzymes

Question 1

What is an Enzyme? give exception.

Answer 1

Are made of proteins, are biological catalysts that speed up a rxn but remain unchanged at the end or by the rxn.

Exception e.g. pepsin, trypsin, chymotrypsin, papain—most enzyme names do end in - “ase”

Question 2

Where are enzymes found?

Answer 2

In all living things.

Question 3

What is Catalysis?

Answer 3

“Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst”

Question 4

Enzymology?

Answer 4

Characterizes 3000 different enzymes

Question 5

Why do most metabolic processes need enzymes?

Answer 5

In order to occur at rates fast enough to sustain life

Question 6

What is Free Energy (Delta G)?

Answer 6

Free energy determines whether a conversion of reactants to products will occur spontaneously
or require a catalyst

Question 7

If a reaction occurs spontaneously, the ΔG is….. and why?

Answer 7

NEGATIVE

Reactions with a negative ∆G release energy, which means that they can proceed w/ out energy input (are spontaneous)

Question 8

What is the rate of the reaction dependent on?

Answer 8

Activation Energy (ΔG‡)

Question 9

If ΔG < 0 (less then zero), being negative, what will happen?

Answer 9

• The reaction will proceed spontaneously

- Meaning the reaction is favourable (exergonic)

Question 10

If ΔG > 0 (greater then zero), being positive, what will happen?

Answer 10

• The reaction will not proceed spontaneously.
• Meaning the reaction is unfavourable (endergonic)

need an input of energy in order to take place (are non-spontaneous).

Question 11

What happens if ΔG = 0 (equal to zero)?

Answer 11

Then the reaction is at equilibrium.

Question 12

Why is the reaction more favourable when the free energy is negative?

Answer 12

as most system wants to achieve a minimum of free energy.

Question 13

What is Activation energy?

Answer 13

The minimum energy which must be available to a

chemical system w/ potential reactants to result in any chemical reaction.

Question 14

What is Activation Energy required for? (B.F.B)

Answer 14

• Bringing reactant(s) together
• Formation of unstable bonds
• Bond rearrangements, etc

Question 15

What does the rate of any reaction depend on?

Answer 15

The magnitude of activation energy - ΔG‡

Question 16

How do enzymes affect the activation energy? (see pics)

Answer 16

Enzymes lower the ΔG‡; thus to speed up the reaction, they lower activation energy.

Question 17

How do Enzymes work? (see pics)

Answer 17

• Catalytic conversion occurs at the enzymes active site.

- Substrate(s) binds at active site.

Question 18

How Enzymes work? part 2 (see pics slide 11)

Answer 18

1: One small part of the enzyme called the Active
Site, complexes with the substrate
2. Enzyme-Substrate Complex - Lock & key fit
3. After the reaction is complete, the products
are released, & enzymes are used again

Question 19

What are the 2 models used to describe the way
enzymes interact with
substrates:

Answer 19

1 - Lock and Key model.

2 - Induced Fit model

Question 20

Describe the ‘lock and key’ model?

Answer 20

• The substrate fits a particular active site like a key fits into a particular lock.
• This theory of enzyme-substrate interaction explains how enzymes exhibit specificity for a particular substrate.

Question 21

Describe the Induced Fit model?

Answer 21

• The enzyme’s active site is not a completely rigid fit for the substrate.
• So the active site will undergo a conformational change when exposed to a substrate to improve binding.

Question 22

What are the 2 advantages This theory of enzyme-substrate interactions based on Induced Fit model compared to the Lock and Key

Answer 22

1 - explains how enzymes may exhibit broad specificity (example: lipase can bind to a variety of lipids).

2 - explains how catalysis may occur (the conformational change stresses bonds in the substrate, increasing reactivity.

Question 23

What are the 2 types of reactions Enzymes carry out? (see pics slide 14)

Answer 23

• Degradative reactions e.g.

- Synthesis reactions e.g.

Question 24

What is the optimum temp. for maximum enzyme activity.

Answer 24

40 degrees Celsius

Question 25

What does low temp. do to enzyme activity?

Answer 25

At low temperature – enzyme activity is

low.

Question 26

what does low kinetic energy affect enzymes?

Answer 26

Movement of molecules is low due to low 
kinetic energy (KE)

Question 27

What happens to enzymes above 40 degrees Celsius?

Answer 27

Enzyme activity decrease above 40 degrees Celsius as the

enzymes become denatured by increase in temperature.

Question 28

What happens to enzymes at 60 degrees Celsius?

Answer 28

Enzyme activity stops at 60oC as all protein

is denatured

Question 29

How does pH affect enzymes?

Answer 29

pH changes the protein shape.

Question 30

Examples of pH

Answer 30

• Pepsin is found in the stomach – optimum pH =3
• Salivary amylase – optimum pH = 6/7
• Alkaline phosphatase – optimum pH = 9/10

Question 31

Many enzymes require a nonprotein cofactor to assist them in carrying out their function what is their name and function?

Answer 31

• Called co-factors or co-enzymes (an organic molecule, such as a vitamin—or an inorganic metal ion; some enzymes require both)

   Function: bind temporarily to the enzyme to

• produce a better fit between the active site and the substrate.
• neutralize repulsive charges between the enzyme and substrate.

Question 32

Some enzymes require only the
polypeptide chain for activity
▪ Others require an additional chemical group: a cofactor

(see pics slide 21)

Answer 32

e. g. - Holoenzyme = apoenzyme + cofactor

- Apoenzyme – protein component of enzyme

Question 33

What is a competitive Inhibition?

see pics slide 22

Answer 33

• A molecule, other than the substrate, binding to the enzyme’s active site
  ▪ The molecule (inhibitor) is structurally and chemically similar to the substrate
  ▪ The competitive inhibitor blocks the active site and thus prevents substrate binding

Question 34

How can Competitive Inhibitors effects be reduced?

Answer 34

by increasing substrate concentration.

Question 35

What is Non-competitive Inhibition?

see pics slide 22

Answer 35

• Involves a molecule (inhibitor) binding to a site other than the active site (an allosteric site).
• This causes a conformational change to the Enzymes active site.
• ## Due to this change, the substrate and active site no longer share Specificity so can’t bind.

Question 36

What can mitigate the Non-competitive inhibitors effect?

Answer 36

• As the inhibitor is not in direct competition w/ the substrate, increasing substrate levels cannot mitigate the inhibitor’s effect.

Question 37

How are enzymatic pathways regulated?

Answer 37

• By Feedback Inhibition.

Question 38

What is Feedback Inhibition?

Answer 38

• This is where the end product of a pathway binds blocks the first enzyme of the pathway
• This binding shuts down the pathway
• No more product is produced!

Question 39

Why do cells use feedback Inhibition?

Answer 39

• Slow down the production
• Conserve energy
• Keep a state of balance within the cell

Question 40

1. Anti-inflammatory drugs that are the inhibitors of cyclooxygenase – Asprin
2. Proton pump inhibitors (PPIs) – Benzopyridines
3. Methotrexate binds to dihydrofolate reductase enzyme approximately 1000-fold more tightly than the substrate and inhibits nucleotide base synthesis. It is used for cancer therapy.
4. Antibiotic penicillin covalently modifies the enzyme transpeptidase, thereby
   preventing the synthesis of bacterial cell walls and thus killing the bacteria.
5. Nucleoside reverse transcriptase inhibitors and protease inhibitors are now
   recommended for treatment of patients with HIV.
6. Statins are used as drugs preventing or slowing the development of
   atherosclerosis.
7. Poisons of plants and invertebrates - inhibiting the action of enzymes involved in Metabolic processes, which disturbs an organism.

Answer 40

READ