Enzyme Kinetics LO

Question 1

what is an enzyme?

Answer 1

biological catalyst that increases rate of reaction without being changed in process

Question 2

what do enzymes do to the activation energy?

Answer 2

decrease it

Question 3

what are 2 ways enzymes lower activation energy?

Answer 3

1. bind during transition state

2. rearrangement of specific active site chemistry

Question 4

how does enzyme lower activation energy when bound during transition state?

Answer 4

enzyme binds to molecule that is in transition state, keeps molecule in transition state until ready to react with other reactant

Question 5

what is meant by covalent chemistry in regards to enzymes?

Answer 5

enzyme creates covalent bond with substrate to help catalyze reaction

Question 6

what is an example of metal ion chemistry in regards to enzymes?

Answer 6

alcohol dehydrogenase has a Zn+2 ion within active site.

- interacts with alcohol using reduction of NAD+ to NADH

Question 7

how does acid/base chemistry work within an enzyme?

Answer 7

enzyme can extract or donate protons to speed up reaction

Question 8

what is a cofactor in an enzymatic reaction?

Answer 8

metallic ions in the active site that assist in biochemical transformations

Question 9

what is a co-enzyme in an enzymatic reaction?

Answer 9

small organic molecules that transport chemical groups from one enzyme to another

Question 10

what is Km?

Answer 10

substrate concentration at which the velocity of the reaction is equal to 1/2 of the Vmax

Question 11

when does the concentration of the substrate equal Km?

Answer 11

when V0 = 1/2 Vmax

Question 12

what is Kcat?

Answer 12

general rate constant that describes the overall rate of the reaction (turnover number)

Question 13

what terms describe the overall efficiency of an enzyme?

Answer 13

Km and Kcat

Question 14

what does a higher Km indicate in regards to the amount of substrate needed to reach 1/2 Vmax?

Answer 14

need more substrate

Question 15

what does a higher Kcat indicate in relation to the speed of the reaction?

Answer 15

faster reaction with higher Kcat

Question 16

what is Kcat equal to?

Answer 16

number of substrate molecules converted to product in given unit of time using single molecule of enzyme when enzyme is saturated with substrate

Question 17

how do you calculate Km from a graph of velocity vs [S]?

Answer 17

locate point on y-axis that looks like 1/2 Vmax, trace across to point on curve, trace down vertically to X-intercept this is Km

Question 18

between cofactors and coenzymes, which chemical groups are “used up”?

Answer 18

coenzymes

Question 19

what is a prosthetic group?

Answer 19

coenzyme or cofactor that is tightly bound to an enzyme

Question 20

what is a haloenzyme?

Answer 20

enzyme with prosthetic group

Question 21

what is a protein in isolation without a prosthetic group?

Answer 21

apoenzyme or apoprotein

Question 22

what are the 4 types of inhibitors?

Answer 22

1. competitive inhibitors
2. non-competitive inhibitors
3. reversible inhibitors
4. irreversible inhibitors

Question 23

what is a competitive inhibitor?

Answer 23

binds to the active site and prevents binding of substrate

Question 24

what do competitive inhibitors do the the Km and the Vmax?

Answer 24

changes Km but not Vmax

Question 25

what does Ritonavir inhibit?

Answer 25

HIV protease, competitive

Question 26

what is methotrexate used in the treatment of?

Answer 26

cancer, competitive

Question 27

what is a non-competitive inhibitor?

Answer 27

binds to allosteric site and prevents binding of substrate

Question 28

what do non-competitive inhibitors do to the Km and Vmax?

Answer 28

changes both Kcat and Vmax but Km remains unchanged

Question 29

what type of inhibitor is lithium and what is it used in the treatment of?

Answer 29

non-competitive, bipolar disorder

Question 30

what is a reversible inhibitor?

Answer 30

binds to enzymes through non-covalent interactions but can be reversed

Question 31

what is a irreversible inhibitor?

Answer 31

covalently modifies enzyme and “kills the enzyme for good”

Question 32

what type of inhibitor is penicillin?

Answer 32

irreversible inhibitor

Question 33

what is the mechanism of penicillin?

Answer 33

binds to DD-transpeptidase which makes cross-links in peptidoglycan molecules in bacteria, bacteria can’t make cell walls and then die

Question 34

what type of inhibitor is DIFP?

Answer 34

irreversible inhibitor

Question 35

what is the mechanism of DIFP?

Answer 35

cleaves serine 195 in chymotrypsin, chymotrypsin then can never covalently bind with its substrates

Question 36

what is an example of covalent modification to activate an enzyme?

Answer 36

phosphorylation can activate or deactivate

Question 37

what binds to trypsin to deactivate it?

Answer 37

BPTI

Question 38

how is trypsinogen activated?

Answer 38

proteolytic cleavage by enteropeptidase turns trypsinogen into trypsin

Question 39

what does uncompetitive inhibition do to Kcat, Vmax and Km?

Answer 39

changes all of them