enzymes 2

Question 1

what is vmax?

Answer 1

enzyme rate when the substrate is saturated

Question 2

what is Km?

Answer 2

concentration at which v = 1/2 Vmax

Question 3

hexokinase vs. glucokinase

Answer 3

hexokinase in peripheral tissues, lower Km
glucokinase in liver, higher km
catalyze same rxn

Question 4

consequence of low vs high km

Answer 4

low km = more activity at lower substrate concentrations

high km= need high substrate concentration for enzyme activity

Question 5

metabolism of ethanol

Answer 5

ethanol to acetaldehyde by alcohol dehydrogenase

acetaldehyde to acetate by acetaldehyde dehydrogenase

Question 6

effects of acetaldehyde

Answer 6

toxic, very reactive

Question 7

consequence of absence of low Km form of acetaldehyde dehydrogenase

Answer 7

mitochondrial form is low Km form, but if this is absent, much use cytosolic form which has high km- this means that there must be a higher substrate concentration for the high Km form to be active and higher concentration of acetaldehyde = more toxic effects, tachycardia and flushing

Question 8

effect of competitive inhibitors on km? vmax?

Answer 8

km will increase

vmax unchanged

Question 9

effect of noncompetitive inhibitors on km? vmax?

Answer 9

km unchanged

vmax will decrease - inhibitor stops the enzyme from working properly

Question 10

effect of organophosphates on AchE active site

Answer 10

organophosphate will form a covalent bond with serine in the active site and prevent AchE from working properly

Question 11

shape of substrate vs. velocity curve for allosteric enzymes

Answer 11

sigmoidal

Question 12

effect of an activator on the curve

Answer 12

shift to left, increased activate at lower [S] = lower km

Question 13

effect of inhibitor on the curve

Answer 13

shifts to right, decreased activity at lower [S] = higher km

Question 14

R state vs t state

Answer 14

R state= low km, high activity

T state = high km, low activity

Question 15

enzyme that regulates pyrimidine synthesis in e. coli

Answer 15

aspartate transcarboxylase

Question 16

activator and inhibitor of aspartate transcarboxylase

Answer 16

activator = ATP
inhibitor = CTP
either can bbd to regulatory site

Question 17

structure of aspartate transcarboxylase

Answer 17

6 catalytic subunits

6 regulatory subunits

Question 18

which aa can be phosphorylated? (3)

Answer 18

serine
threonine
tyrosine

Question 19

what is the effect of phosphorylation?

Answer 19

gives (-) charge, allows for the formation of more H bonds

Question 20

describe regulation of protein kinase A

Answer 20

cAMP bind to the regulatory subunits, causing them to dissociate from the catalytic subunits, catalytic subunits free to bind substrate

Question 21

what is the regulatory subunit of PKA an example of?

Answer 21

“pseudo-substrate”

Question 22

effects of epinephrine on blood sugar

Answer 22

epinephrine increases blood sugar through a cAMP dependent mechanism- PKA will phosphorylate and activate phosphorylase (breaks down glycogen into glucose) AND will phosphorylate and inactivate glycogen synthase (synthesizes glycogen) == increased blood glucose

Question 23

how does calmodulin active enzymes?

Answer 23

calmodulin-activated kinases are auto inhibited with pseudo-substrate, once activated, calmodulin will bind the pseudo-substrate to release the auto inhibition and free the active site to function as kinase

Question 24

example of calmodulin dependent kinase

Answer 24

MLCK