16.3 : Prokaryotic regulation

Question 1

positive control

Answer 1

increases frequency

Question 2

activators

Answer 2

enhance binding of RNA polymerase to promoter

Question 3

negative control

Answer 3

decreases frequency

Question 4

repressor

Answer 4

bind to regulatory sites on DNA called operators that prevent or decrease initiation frequency

Question 5

effector molecules

Answer 5

can act on both repressors and activators

Question 6

prokaryotic cells often respond to their environment by changes in …

Answer 6

gene expression

Question 7

induction

Answer 7

enzymes for a certain pathway are produced in response to a substrate

Question 8

repression

Answer 8

capable of making an enzyme but does not

Question 9

lac operon

Answer 9

encodes proteins necessary for the use of lactose as an energy source

lacZ, lacY, lacA

Question 10

gene for the lac repressor (lacl)

Answer 10

is linked to the rest of the lac operon

Question 11

The lac operon is negatively regulated by a ______ ________

Answer 11

repressor protein

Question 12

(negative regulation of the lac operon)
lac repressor binds to the _____ to ______ transcription

Answer 12

operator; block

Question 13

(negative regulation of the lac operon)
In the presence of lactose, an inducer molecule (_______) binds to the repressor protein

repressor can no longer ____ to operator

transcription _____

Answer 13

allolactose; bind; proceeds

Question 14

even in the absence of lactorse, the lac operon is expressed at a very ____ level

Answer 14

low

Question 15

glucose repression

Answer 15

a mechanism for the preferential use of glucose in the presence of other sugars

Question 16

(glucose repression)
______ used first, then ______

Answer 16

glucose; lactose

Question 17

(glucose repression)
mechanism involves an activator protein that ______ transcription

Answer 17

stimulates

Question 18

Catabolic activator protein

Answer 18

(CAP) an allosteric protein with cAMP as effetor

Question 19

(glucose repression)
level of cAMP in cells is ____ in the presence of glucose so that no stimulation of transcription from CAP responsive operons take place

Answer 19

reduced

Question 20

inducer exclusion

Answer 20

presence of glucose inhibits the transport of lactose into the cell

Question 21

What does the trp operon encode for?

Answer 21

encodes genes for the biosynthesis of tryptophan

Question 22

Is the trp operon expressed when the cell contains sufficient amounts of tryptophan?

Answer 22

No

Question 23

Is the trp operon expressed when levels of tryptophan are low?

Answer 23

Yes

Question 24

trp repressor

Answer 24

a helix turn helix protein that binds to the operator site located adjacent to the trp promoter

Question 25

What is the trp negatively regulated by?

Answer 25

the trp repressor protein

Question 26

(negative regulation of the trp operon)

trp repressor binds to the operator to. ______ transcription

Answer 26

block

Question 27

(negative regulation of the trp operon)

binding of repressor to the operator requires a ______ which is tryptophan (operon is repressed)

Answer 27

corepressor

Question 28

(negative regulation of the trp operon)

When tryptophan levels fall, the repressor, can the repressor bind to the operator? (operon is derepressed, versus being induced)

Answer 28

No

Question 29

How does tryptophan binding alter repressor conformation?

Answer 29

• increases the distance between the two recognition helices
• repressor can then fit snugly into two adjacent portions of the major groove in DNA