ATCase Flashcards

1
Q

ATCase catalyses

A

first step of biosynthesis of pyrimidines

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2
Q

ATCase does not follow

A

M-M kinetics

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3
Q

allosterically inactivated by

A

CTP

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4
Q

allosterically activated by

A

ATP

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5
Q

CTP

A

pyrimidine nucleotides

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6
Q

ATP

A

purine nucleotides

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7
Q

CTP and ATP are like

A

competitive inhibiter–> increase Km but do not affect Vmax

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8
Q

allosteric effectors that show a sigmoidal graph are referred to as

A

K system effectors

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9
Q

to make nucleic acid pyrimidine and purines have to be

A

in equal amounts

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10
Q

too much ATP

A

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

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11
Q

too much CTP

A

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

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12
Q

structure of ATCase

A

300KDa

C6R6

x2 C3 trimers

x3 R2 dimers

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13
Q

r

A

regulatory subunit

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14
Q

C

A

catalytic subunit

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15
Q

competitive inhibiter of ATCase

A

PALA

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16
Q

crystal structure in the presence of

17
Q

PALA and ATCase

A

causes changes to the quaternary strucure

18
Q

ATCase has 2 distinct forms

A

T state- tense

R state -relaxed

19
Q

T state

A

tense

-CTP is binded and therefore not active

20
Q

R state

A

relaxed

-ATP is binded and therefore active

21
Q

CTP stabilises

22
Q

ATP stabilised

23
Q

shape of graph

A

sigmoidal instead of hyperbolic due to co-opertivity

24
Q

co-opertivity

A

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

25
positive coop
binding of substrate to one subunit increases the likelihood of other subunits binding
26
negative coop
rare, but when binding to one subunit reduces the likelihood of the substrate binding
27
two models of Coopertivity
Concerted | Sequential
28
Sequential model discovered by
Koshland , Nemethy and Elmer
29
The sequential model
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
30
The concerted model was discover by
Monod, Wyman and Chnageux
31
the concerted model
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
32
which model is more acceptedL
concerted model since it explains enzyme behaviour better