Operons

Question 1

what do prokaryotic operons contain

Answer 1

operators - segment of DNA that regulates activity of the structural genes of the operon

Question 2

what happens if operator is bound by a repressor molecule

Answer 2

RNA pol is blocked and does not produce mRNA

Question 3

what does an inducer molecule do

Answer 3

it binds to repressor hence changing its shape and now can no longer bind to the operator

transcription proceeds

Question 4

lac operon codes for what proteins

Answer 4

lacZ, lacY, lacA

Question 5

what does lacZ code for

Answer 5

beta galactosidase - hydrolyzes lactose to galactose and glucose

Question 6

what does lacY code for

Answer 6

permease - facilitates movement of lactose into the cell

Question 7

what does lacA cod for

Answer 7

thiogalactoside transacetylase - acetylases lactose

Question 8

when are the proteins of lac operons maximally produced

Answer 8

when lactose is available to the cell but glucose is not

Question 9

what codes for the repressor protein

Answer 9

lacI gene

Question 10

what happens to the lac operon when only glucose is present

Answer 10

lac operon is repressed

Question 11

mechanism that the lac operon uses to repress itself

Answer 11

repressor binding protein binds to the operator site downstream of promoter region via a helix-turn-helix motif

Question 12

lac operon being repressed is an example of what type of regulation

Answer 12

negative regulation

Question 13

when is the lac operon maximally expressed

Answer 13

when only lactose is availabe

Question 14

when only lactose present what is used to stop the repressor protein

Answer 14

allolactose - isomer of lactose

Question 15

what does allolactose do

Answer 15

it binds to repressor protein and changes it conformation hence stopping it from binding the operon

Question 16

what enzyme is active when glucose not present but lactose is

Answer 16

adenylyl cyclase - cAMP is made and binds to CAP protein

Question 17

what does the cAMP-CAP trans acting complex do

Answer 17

binds to CAP site making RNA pol more efficiently initiate transcription at promoter sie

Question 18

cAMP-CAP doing it job is an example of what type of regulation

Answer 18

positive regulation

Question 19

what happens with the mRNA produced after initiation of the lac peron

Answer 19

it produces the three proteins - lacZ, lacA, lacY

Question 20

what happens with the transcription of lac operon when both glucose and lactose available

Answer 20

it is negligible because adenylyl cyclase is inhibited by the glucose

Question 21

what role does the repressor protein play when both glucose and lactose are present

Answer 21

it could remain unbound but no lac operon would be transcribed because glucose is inhibiting the adenylyl cyclase from forming he cAMP-CAP trans acting complex