Lecture 3 - Enzymes

Question 1

What is the definition of enzymes?

Answer 1

-biological catalysts
-made of protein
-increase rate of chemical reaction
-specific to their action with 1 substrate
-need to maintain structure to keep function

Question 2

What is a cofactor?

Answer 2

non-protein inorganic (metal ion) that helps enzyme

Question 3

What is an organic cofactor called?

Answer 3

coenzyme

Question 4

What are the 2 types of coenzymes?

Answer 4

prosthetic groups: permanently bound
cosubstrates: temporarily bound

Question 5

What are important coenzymes?

Answer 5

ATP/GTP
NAD
FAD
coenzyme A

Question 6

What are examples of cofactors?

Answer 6

Mg2+
Ca2+

Question 7

What is the difference between an apoenzyme and a holoenzyme?

Answer 7

apoenzyme = inactive (enzyme WITHOUT cofactor)
holoenzyme = active (apoenzyme + cofactor)

Question 8

What is the active/catalytic site of an enzyme?

Answer 8

site where substrate must fit and bind to activate enzyme

Question 9

How many classes of enzymes exist?

Answer 9

1. oxidoreductase
2. transferase
3. hydrolase
4. lyase
5. isomerase
6. ligase/synthetase
7. translocase

Question 10

What is an exergonic and endergonic reaction?

Answer 10

exergonic = release energy
endergonic = requires energy

Question 11

What is the Michaelis-Menten formula used for?

Answer 11

-formula to interpret behavior of enzymes (regulatory enzymes)
-calculate rate of catalysis of enzyme at some particular substrate

Question 12

What happens in the catalytic reaction of the concentration of substrate is increased?

Answer 12

low [S] = velocity increases 1:1
high [S] = no change in velocity (plateaus)

Question 13

Can enzymes catalyze 2 or more substrates?

Answer 13

yes, many enzymes catalyze reactions with 2+ substrates

Question 14

Is the pH different for different enzymes?

Answer 14

yes, every enzyme has optimum pH for maximal activity

Question 15

What are the factors affecting enzymatic activity?

Answer 15

temp
water (required reactant)
pH
[substrate]
[enzyme]
inhibitors
end products
activators
radiation

Question 16

What kinds of enzyme inhibitors exist?

Answer 16

reversible
irreversible

Question 17

What are the kinds of reversible enzyme inhibition?

Answer 17

competitive
uncompetitive
mixed
non-competitive

Question 18

What is an irreversible enzyme inhibitor?

Answer 18

bind covalently to enzyme’s active site (blockage) –> can destroy functional groups that are needed for enzyme’s function

Question 19

What is competitive inhibition?

Answer 19

binds to substrate active site

Question 20

What is non-competitive inhibition?

Answer 20

binds to enzyme-substrate complex –> changes shape of active site –> can’t bind

Question 21

What is the difference between competitive and non-competitive and uncompetitive inhibition?

Answer 21

competitive competes directly with substrate (increasing substrate can overcome)
non-competitive/uncompetitive do NOT compete directly with substrate (increasing substrate CANNOT overcome)

Question 22

What is an allosteric site?

Answer 22

site other than enzyme’s active site

Question 23

What is allosteric regulation?

Answer 23

binding regulator molecule to allosteric site

Question 24

What is an allosteric activator?

Answer 24

effectors/regulators that enhance protein’s activity

Question 25

What is an allosteric inhibitor?

Answer 25

effectors/regulators that decrease protein’s activity?

Question 26

What is a reversible covalent modification of an enzyme?

Answer 26

between non-protein group and enzyme to turn it on or off

Question 27

What are examples of reversible covalent modification of an enzyme?

Answer 27

-phosphorylation (can be dephosphorylated)
-adenylation
-uridylation

Question 28

What is proteolytic activation?

Answer 28

enzymes, hormones, proteins made as inactive proteins
activation = cleavage of 1 or a few specific peptide bonds (no ATP required)
irreversible!

Question 29

What are zymogens?

Answer 29

inactive precursor of protein