ATCase

Question 1

ATCase catalyses

Answer 1

first step of biosynthesis of pyrimidines

Question 2

ATCase does not follow

Answer 2

M-M kinetics

Question 3

allosterically inactivated by

Answer 3

CTP

Question 4

allosterically activated by

Answer 4

ATP

Question 5

CTP

Answer 5

pyrimidine nucleotides

Question 6

ATP

Answer 6

purine nucleotides

Question 7

CTP and ATP are like

Answer 7

competitive inhibiter–> increase Km but do not affect Vmax

Question 8

allosteric effectors that show a sigmoidal graph are referred to as

Answer 8

K system effectors

Question 9

to make nucleic acid pyrimidine and purines have to be

Answer 9

in equal amounts

Question 10

too much ATP

Answer 10

ATCase is activated to synthesise pyrimidine nucleotides until conc of ATP and CTP become balanced

Question 11

too much CTP

Answer 11

ATCase is inhibited by CTP, therefor permits purine nucleotide biosynthesis to balance ATP and CTP

Question 12

structure of ATCase

Answer 12

300KDa

C6R6

x2 C3 trimers

x3 R2 dimers

Question 13

r

Answer 13

regulatory subunit

Question 14

C

Answer 14

catalytic subunit

Question 15

competitive inhibiter of ATCase

Answer 15

PALA

Question 16

crystal structure in the presence of

Answer 16

PALA

Question 17

PALA and ATCase

Answer 17

causes changes to the quaternary strucure

Question 18

ATCase has 2 distinct forms

Answer 18

T state- tense

R state -relaxed

Question 19

T state

Answer 19

tense

-CTP is binded and therefore not active

Question 20

R state

Answer 20

relaxed

-ATP is binded and therefore active

Question 21

CTP stabilises

Answer 21

T state

Question 22

ATP stabilised

Answer 22

R state

Question 23

shape of graph

Answer 23

sigmoidal instead of hyperbolic due to co-opertivity

Question 24

co-opertivity

Answer 24

binding of the substrate to one Active site favours the conversion of the entire enzyme into the R state 000> increasing activity at other active sites

Question 25

positive coop

Answer 25

binding of substrate to one subunit increases the likelihood of other subunits binding

Question 26

negative coop

Answer 26

rare, but when binding to one subunit reduces the likelihood of the substrate binding

Question 27

two models of Coopertivity

Answer 27

Concerted

Sequential

Question 28

Sequential model discovered by

Answer 28

Koshland , Nemethy and Elmer

Question 29

The sequential model

Answer 29

binding of the substrate to one subunit moves the subunit to the relaxed state

-makes it more likely neighbouring subunits will bind to the neighbouring subunits

Question 30

The concerted model was discover by

Answer 30

Monod, Wyman and Chnageux

Question 31

the concerted model

Answer 31

entire enzyme will switch from T state to R state in one go

• likelihood of this is determined by the number of substrate molecules bound
• after the switch binding of further substrate is more likely

Question 32

which model is more acceptedL

Answer 32

concerted model since it explains enzyme behaviour better