Chapter 16: Control of Gene Expression in Prokaryotes

Question 1

Structural Genes

Answer 1

encoding proteins that “make or break”

Question 2

Regulatory Genes

Answer 2

encoding products that interact with other sequences and affect the transcription and translation of these sequences

Question 3

Regulatory Elements

Answer 3

DNA sequences that are not transcribed but play a role in regulating other nucleotide sequences

Question 4

What makes expression constituitive?

Answer 4

if a gene is continuously expressed under normal cellular conditions

Question 5

If a cell is undergoing catabolite repression, what kind of control is it undergoing?

Answer 5

Positive

Question 6

What type of positive control uses CAP, cAMP, and glucose to repress the metabolism of other sugars?

Answer 6

Catabolite repression

Question 7

Where do CAP and cAMP bind?

Answer 7

slightly upstream of the lac gene promoter

Question 8

What is inversely proportional to the level of available glucose?

Answer 8

cAMP

Question 9

What is positive control?

Answer 9

-stimulate gene expression by using a regulatory protein is an activator
-has to be turned on

Question 10

How does catabolite repression function when glucose is low?

Answer 10

-levels of cAMP are high and it readily binds to CAP. ONce binded to the DNA, DNA polymerase increases binding efficiency
-RESULTS: high rates of transcription and translation of structural genes AND the production of glucose from lactose

Question 11

How does catabolite repression function when glucose is high?

Answer 11

levels of cAMP are low and less likely to bind to CAP. RNA polymerase cannot bind as efficiently so transcription is low

Question 12

What is negative gene expression?

Answer 12

-needs to be turned off
-inhibit gene expression; regulatory protein is a repressor

Question 13

What stage are most proteins regulated in?

Answer 13

transcription

Question 14

What are the different shapes within a protein?

Answer 14

domains

Question 15

What is significant about the domains of a protein?

Answer 15

~60-90 amino acids that are responsible for binding to DNA and forms hydrogen bonds

Question 16

What is the specific shape that is found within a domain?

Answer 16

motif

Question 17

What is significant about motifs?

Answer 17

a simple structure that fits into the major groove of the DNA

Question 18

What is a helix-turn-helix motif?

Answer 18

-regulatory in prokaryotes
-contains a DNA-binding helix, turn, then a dimer binding helix

Question 19

What is the signifigance of a zinc finger motif?

Answer 19

eukaryotic regulation

Question 20

What is the signifigance of a leucine zipper motif?

Answer 20

eukaryotic regulation

Question 21

What is an operon?

Answer 21

group of genes sharing a common promoter and are transcribed as a unit

Question 22

What is a promoter+ additional sequences that control transcription (operator)+ structural genes?

Answer 22

operon

Question 23

Are operons more common in prokaryotes or eukaryotes?

Answer 23

typical in prokaryotes but not in eukaryotes

Question 24

How were operons discovered?

Answer 24

found by investigating decision of E.coli to eat glucose or lactose

Question 25

What is a regulator gene?

Answer 25

DNA sequence that encodes products that affect the operon function, but are not part of the operon

Question 26

How can regulator genes regulate transcription of mRNA?

Answer 26

regulator genes must have their own promoter that encodes for a regulatory protein. It must then bind to the operator site

Question 27

What type of operon has transcription off and needs to have it turned on?

Answer 27

inducible operons

Question 28

What type of operon has transcription turned on and needs it be turned off?

Answer 28

repressible operon

Question 29

What is the function of the lac operon?

Answer 29

it is a negative, inducible operon that functions in lactose metabolism

Question 30

What is the inducer in the lac operon?

Answer 30

allolactose

Question 31

lacI

Answer 31

repressor encoding gene

Question 32

lacP

Answer 32

operon promoter

Question 33

What is contained in the lacP?

Answer 33

-35 and -10 consensus sequences

Question 34

lacO

Answer 34

operon operator

Question 35

lacZ

Answer 35

encoding B-galactosidase

Question 36

lacY

Answer 36

encoding permease

Question 37

What is the function of permease?

Answer 37

actively transprots lactose into the cell where B-galactosidase breaks it into galactose and glucose

Question 38

What is the function of B-galactosidase?

Answer 38

-breaks lactose into glactose and glucose and the related compound of allolactose (to then be converted to galactose and glucose)

Question 39

lacA

Answer 39

encoding transacetylase

Question 40

Does the repression of the lac operon completely shut down transcription?

Answer 40

no

Question 41

How does the regulatory protein function in the absence of lactose?

Answer 41

the repressor binds to the operator and inhibits transcription

Question 42

What does it mean that the lacI+ gene is transdominant?

Answer 42

the repressor produced can bind to both operartors and repress transcription in the anbsence of lactose

Question 43

How does the regulator protein function in the prescence of lactose?

Answer 43

some of the lactose is converted to allolactose. This binds to the regulator protein making it inactive

Question 44

What happens to the structrual genes of of the lac operon in the prescence of lactose?

Answer 44

they are transcribed and translated since the regulator cannot bind to the operator

Question 45

When is functional B-galactosidase produced from the lacZ+ gene?

Answer 45

when lactose is present and it has inactivated the repressor

Question 46

What does the lacI gene produce in the prescence of lactose?

Answer 46

a super repressor that does not bind lactose and is transdominant

Question 47

What is a partial diploid?

Answer 47

full bacterial chromosome+ an extra piece of DNA on F plasmid

Question 48

How does the partial diploid function in the absence of lactose?

Answer 48

active represssor binds to the operator which creates B-galatosidase

Question 49

How does the partial diploid function in the prescence of lactose?

Answer 49

lactose binds to the repressor, which inactivates it and produces nonfunctional B-galactosidase

Question 50

What affects the structure of the enzymes but not the regualtion of their synthesis?

Answer 50

structural gene mutations

Question 51

Where do structural gene mutations occur and affect?

Answer 51

only affect lacZ or lacY and only occur on lacZ/lacY

Question 52

What affects the transcription of trans structrual genes?

Answer 52

regulator gene mutations

Question 53

What gene leads to constitutive transcription of three structural genes?

Answer 53

lacI-

Question 54

What is dominant over lacI- and is trans acting?

Answer 54

lacI+ is dominant and a single copy brings about normal regulation of lac operon

Question 55

What do operator mutations affect?

Answer 55

affect transcription of structural genes; cis

Question 56

Is an operator mutation dominant or recessive?

Answer 56

dominant over lacO+

Question 57

What do promoter mutations affect?

Answer 57

transcription of structural genes

Question 58

What is the trp operon?

Answer 58

a negative repressible operon that is composed of 5 structural genes

Question 59

What works together to convert chorismate to trytophan?

Answer 59

-the 5 structural genes -trpE, trpD, trpC, trpB, and trpA

Question 60

How does the trp operon function when trp is low?

Answer 60

the trp repressor is noramlly inactive and cannot bind to the operator so transcription occurs

Question 61

How does the trp operon function when trp is high?

Answer 61

trp binds to the repressor and activates it. The repressor then binds to the operator and shuts transcription off

Question 62

What affects the continuation of transcription, not its initiation?

Answer 62

attenuation

Question 63

What action terminates transcription before it reaches the structural genes?

Answer 63

attenuation

Question 64

How does attenuation work in the trp operon when trp is high?

Answer 64

region 1 binds to region 2, which causes the binding of region 3 and 4 -premature transcription termination

Question 65

How does attenuation work in the trp operon when trp is low?

Answer 65

region 2 pairs with region 3 and termination does not occur in transcription

Question 66

Antisense RNA

Answer 66

complementary to targeted partial sequence of mRNA; they function by going to influence translation somewhere else

Question 67

Riboswitches

Answer 67

molecules influence the fomration of secondary structures in mRNA; RNA that has to bind to an RNA molecule to allow it to be linear and disrupt base pairing to prevent translation

Question 68

Ribozymes

Answer 68

mRNA molecules with catalytic activity