Lecture 3.5: Enzyme Regulation

Question 1

Regulation of enzyme activity is mediated by:

Answer 1

1. RNA synthesis
2. RNA processing
3. Protein synthesis
4. Protein targeting
5. Protein degredation
6. binding of regulatory molecules
7. covalent modification
8. proteolytic processing

Question 2

Allosteric Regualtion

Answer 2

2 active sites
do not conform to michaelis-menten kinetics

Question 3

Allosteric effectors (modulators) bind to specific [ ] sites and [ ]

Answer 3

regulatory (allosteric)
alter enzyme acitivty

Question 4

Allosteric activators trends

Answer 4

curve shifts left
increased binding affinity
may stimulate activity

Question 5

Allosteric inhibitors

Answer 5

curve shifts right
decreased binding affinity
may decrease activity

Question 6

ATCase catalyzes first step in [ ]

Answer 6

pyrimidine biosynthesis

Question 7

ATCase displays a [ ] curve

Answer 7

sigmoidal

Question 8

ATCase substrates?

Answer 8

Carbamoyl phosphate
L-aspartate

Question 9

ATCase inhibitor?

Answer 9

cytidine-triphosphate (CTP)

Question 10

ATCase activator?

Answer 10

ATP

Question 11

CTP affects on ATCase

Answer 11

CTP is not structurally similar to substrate so allosteric inihibitor
Decreases activity of ATCase
binds to regulatory subunits and stabilizes T state
shifts curve right

Question 12

ATP on ATCase

Answer 12

Increases activity of ATCase
binds to regulatory subunits and stabilizes R state
shifts curve left

Question 13

ATCase is composed of [ ] protein complexes forming the functional [ ] complex

Answer 13

Two C3R3 trimeric protein complexes
C6R6 ATCase complex

Question 14

When ATCase is in its R-state what happens?

Answer 14

increased distance between the catalytic trimers

Question 15

covalent modifications

Answer 15

reversible modifications that can rapidly regualte catalytic efficiency of enzymes
* Phophorylation
* Adenylylation

Question 16

Phosphorylation

Answer 16

is catalyzed by kinase and requires the expenditure of ATP

Question 17

amino acids involved in phosphorylation

Answer 17

serine
threonine
tyrosine
histidine can be phosphorylated but its too fast

Question 18

Phosphatase

Answer 18

catalyzes cleavage of phosphate ester bond with water
removal of phosphoryl group

Question 19

Phosphorylation-dephosphorylation results in a what structural and chemical changes

Answer 19

addition of negative charges changes electrostatic interactions and conformation
phosphoryl group can form H-bonds

Question 20

Glycogen phosphorylase regulated by?

Answer 20

by phosphorylation in response to hormone signaling

Question 21

Glucagon and Epinephrine role on glycogen phosphorylase

Answer 21

low levels of glucose = glucagon
glucagon + epinephrine stimulate phosphorylase kinase to activate glycogen phosphorylase
addition of ATP further stimulates

Question 22

Insulin roles on glycogen phosphorylase

Answer 22

high level of glucose = insulin
insulin stimulates protein phosphatase 1 to deactivate glycogen phosphorylase
addition of water further deactivates

Question 23

Insulin roles on glycogen phosphorylase

Answer 23

high level of glucose = insulin
insulin stimulates protein phosphatase 1 to deactivate glycogen phosphorylase
addition of water further deactivates

Question 24

proteolytic processing is an [ ] process

Answer 24

irreversible

Question 25

zymogens

Answer 25

inactive precursor enzymes
* trypsinogen
* chymotrypsinogen
* protoelastase
* procarboxy-peptidase
* prolipase

Question 26

most pancreatic proteases are synthesized as [ ]

Answer 26

inactive precursors

Question 27

proteolytic cleavage can [ ] enzymes

Answer 27

activate
removal of amino acid segment generates the active enzyme

Question 28

Chymotrypsin is activated by [ ]

Answer 28

proteolytic cleavage
1. chymotrypsinogen is cleaved by trypsin
2. two π chymotrypsin segments are formed from the cleavage between L13 and S14 + R15 and I16 & Y146 and T147 + N148 and A149

chymotrypsin is stabilized by disulfide bonds