ch 19: control of gene expression in bacteria

Question 1

what 3 levels can genes be regulated at?

Answer 1

1. transcriptional control
2. translational control
3. post-translational control

Question 2

transcriptional control

Answer 2

the cell could make mRNAs only for proteins it needs
- slow response but saves the most energy

Question 3

translational control

Answer 3

the cell could prevent the mRNAs for unneeded proteins from being translated
- more rapid change than transcriptional control

Question 4

post-translational control

Answer 4

change protein activity by chemical modifications
- fastest response but costs lots of energy

Question 5

transcription factors

Answer 5

recognize specific sequences of bases in DNA based on shape and partial charge to make hydrogen bonds

Question 6

negative control

Answer 6

regulatory protein shuts down transcription
-repressor protein

Question 7

positive control

Answer 7

regulatory protein triggers transcription
- activator protein

Question 8

can genes be controlled by multiple transcription factors?

Answer 8

yes

Question 9

operon

Answer 9

a group of genes that are transcribed together and regulated by a shared promoter and operator
- only in prokaryotes

Question 10

inducer

Answer 10

small molecule that triggers transcription of a gene

Question 11

operator

Answer 11

sequence of DNA that a transcription factor binds to

Question 12

activator

Answer 12

transcription factor protein that promotes transcription

Question 13

repressor

Answer 13

transcription factor protein that decreases transcription

Question 14

what genes are required to digest lactose

Answer 14

lac operon: b-galactosidase and galactoside permease

Question 15

b-galactosidase

Answer 15

breaks lactose down into 2 monomers: glucose and galactose

Question 16

what is lac operon regulated by?

Answer 16

inducible repressor

Question 17

what happens if lactose is absent?

Answer 17

repressor activated, operon not expressed

Question 18

catabolite activator protein (CAP)

Answer 18

activated when cAMP is present

Question 19

when glucose is high, what happens?

Answer 19

there is no cAMP synthesis and CAP does not bind to activate lac operon expression

Question 20

what happens if glucose is low?

Answer 20

cAMP binds to CAP and activates the lac operon expression

Question 21

what happens if lactose and glucose are present?

Answer 21

repressor inactivated, activator not activated, operon expressed at low levels

Question 22

what happens if lactose is present and glucose is absent?

Answer 22

repressor inactivated, CAP activated, operon expressed at higher levels

Question 23

what is the trp operon regulated by?

Answer 23

repressible repressor

Question 24

if tryptophan is high, what happens?

Answer 24

the trp repressor is active and transcription does not occur

Question 25

if tryptophan is low, what happens?

Answer 25

trp repressor is inactive and transcription for tryptophan proteins occurs

Question 26

global gene regulation

Answer 26

coordination regulation of many genes

Question 27

regulon

Answer 27

a set of separate genes and operons that contain the same regulatory sequences and are controlled by a single type of regulatory protein

Question 28

when are regulons differentially expressed?

Answer 28

in response to a particular challenge such as sudden rise in temp, loss of nutrients, shift to new environment, etc