Topic 3-L3 - Enzymes

Question 1

(generally) Proteins made by cells that act as

Answer 1

catalysts

Question 2

There are RNA enzymes as well, called

Answer 2

ribozymes

Question 3

Vast majority of enzymes are

Answer 3

proteins – metabolism mediated by

protein enzymes

Question 4

Are catalysts specific to specific rxns?

Answer 4

Yes

Question 5

Enzyme names generally end with the “___” suffix.

Answer 5

ase

Question 6

Formation of H2O is exergonic and energetic s are favourable, but won’t occur without catalyst why?

Answer 6

Activation energy way to high and needs to be lowered

Question 7

Enzymes work by lowering the

Answer 7

activation energy of a reaction, therefore increasing the rate for rxn

Question 8

Do catalysts change energetics of ΔG or equilibrium of rxn

Answer 8

They do NOT change the energetics (ΔG) or the equilibrium of the reaction

Question 9

How do enzymes lower the activation energy of a reaction??

Answer 9

• Local concentrations of substrates are increased at the active site of the enzyme
• enzymes alter the electronic distribution and
  conformational structure of the substrate(s), which enhances reactivity.
• stabilization of transition metals

Question 10

Catalysts stabilizing transition metals involve

Answer 10

the use of coenzymes or prosthetic

groups – some use metallic elements (E.g. - Fe, Mg, Zn, Co…)

Question 11

Steps for a enzyme-catalyze rxn

Answer 11

1) substrate bound to enzyme active site
2) enzyme substrate complex forms
3) strain is placed on bond
4) produces are released
5) enzyme is ready to begin new catalytic cycle

Question 12

How do enzymes influence cell metabolism?

Answer 12

Enzymes catalyze specific reactions, allowing the for accumulation of those specific products

• In metabolic pathways, products from one reaction are the reactants in the next – prevents accumulation of products of the individual reactions (accumulation of products promotes the reverse reaction)

Question 13

Most biological reactions will not occur at a significant rate in the absence of an enzyme ?

Answer 13

Yes

Question 14

Enzyme activities can be controlled by regulating the amounts of the

Answer 14

enzymes or by controlling their activity (via competetive inhibitors)

Question 15

Competitive inhibitors of an

Answer 15

enzyme “fit” in the same active sit as

the substrates – inhibit substrate binding (and thus the reaction)

Question 16

Competetive inhibitors is the way many drugs work (example below is from

Answer 16

sulfa drugs – antibiotics that inhibit folate biosynthesis)

Question 17

Positive effector (“allosteric activator”):

Answer 17

Promotes binding of substrate and catalysis

Question 18

Negative effector (“allosteric inhibitor”):

Answer 18

Prevents substrate from binding

Question 19

Types of effectors

Answer 19

postive (allosteric activator) and negative (allosteric inhibitor)

Question 20

Allosteric activators steps for action

Answer 20

1. Effector binds to allosteric site
2. Causes conformational change in active site
3. Substrate fits into active site
4. Substrate will be converted to product

Question 21

Allosteric inhibitors steps for action

Answer 21

1) Effector binds at regulatory site
2) Causes conformational change in active site
3) Substrate can not bind (no “fit” in active site)
4) Reaction inhibited

Question 22

Absences of effector causes

Answer 22

• Substrate binds to active site

- Catalysis proceeds

Question 23

Feedback inhibition is A common strategy used to

Answer 23

control metabolic pathways

Question 24

Feedback inhibition:

Answer 24

• End product is negative modulator:
• Binds to first enzyme in pathway & inhibits its activity.
• End product shuts down its own production when it’s in excess
• Once end product used up, pathway resumes