chapter 12 part 1

Question 1

constitutive transcription

Answer 1

occurs for genes needed continuously to perform housekeeping tasks, needed for life of the cell

Question 2

regulated transcription/inducible genes

Answer 2

for genes only needed for responses to changing environmental conditions or during certain phases of growth

Question 3

what does regulated transcription include the control of

Answer 3

imitation and amount of transcription

Question 4

what is the major means of regulating gene expression bacteria

Answer 4

transcriptional regulation

Question 5

what mechanisms are also important for gene expression

Answer 5

post-transcriptional mechanisms

Question 6

negative control of transcription

Answer 6

involves binding of a repressor protein to a regulatory DNA sequence and preventing transcription

Question 7

where do repressors bind

Answer 7

operators through DNA-binding domain

Question 8

does negative control turn on or off genes

Answer 8

both

Question 9

positive control of transcription

Answer 9

involves binding of an activator protein to regulatory DNA and initiating gene transcription

Question 10

binding of activator to DNA causes what?

Answer 10

RNA polymerase to initiate transcription

Question 11

does positive control turn on or off genes

Answer 11

both

Question 12

what 2 domains do activator/repressor proteins have?

Answer 12

• DNA binding domain
• allosteric domain

Question 13

activator and repressor proteins are examples of what?

Answer 13

transcription factors

Question 14

DNA-binding domain

Answer 14

locates and binds operator DNA sequence or other target DNA sequences

Question 15

allosteric domain

Answer 15

binds a molecule or protein, which causes a change in conformation of the DNA-binding domain, altering its function

Question 16

allostery

Answer 16

to turn DNA binding function on or off

Question 17

4 categories of gene regulation

Answer 17

1. negative inducible
2. negative repressible
3. positive inducible
4. positive repressible

Question 18

inducible

Answer 18

the effector molecule causes transcription to start

Question 19

repressible

Answer 19

the effect molecule causes transcription to stop

Question 20

all 4 categories of gene regulation require the participation of an additional…

Answer 20

allosteric effector/inducer/inhibitor/corepressor moelcule

Question 21

negative inducible

Answer 21

• TF = repressor
• binding of effector molecule to TF causes transcription to start
• effector molecule is inducer

Question 22

ex. of negative inducible

Answer 22

Lac operon

Question 23

negative repressible

Answer 23

• TF = repressor
• binding of effector molecule to TF causes transcription to stop
• effector molecule is co-repressor

Question 24

ex. of negative repressible

Answer 24

Trp operon

Question 25

positive inducible

Answer 25

- TF = activator - binding of effector molecule to TF causes transcription to start (co-activator) - effector molecule is inducer

Question 26

positive repressible

Answer 26

- TF = activator - binding of effector molecule to TF causes transcription to stop - effector molecule is inhibitor

Question 27

bacterial regulatory DNA sequences frequently have what?

Answer 27

inverted or direct repeats

Question 28

each polypeptide of a regulatory homodimer interacts with what?

Answer 28

one repeat

Question 29

most common structural feature of homodimer (repeat) proteins in bacteria

Answer 29

helix-turn-helix motif (HTH)

Question 30

helix-turn-helix (HTH) motif

Answer 30

two a-helical regions interact with the DNA sequences

Question 31

a recognition and a stabilizing helix are separated by a ________ in each polypeptide

Answer 31

turn

Question 32

operon

Answer 32

clusters of genes undergoing coordinated transcriptional regulation by a shared regulatory region

Question 33

where are operons commonly found?

Answer 33

bacterial genomes

Question 34

genes in an operon nearly always participate in what?

Answer 34

the same metabolic or biosynthetic pathway

Question 35

can an operon be activated or repressed

Answer 35

both

Question 36

switching between activated/repressed are typically responsive to what?

Answer 36

environmental cues

Question 37

how many proteins does the lactose (lac) operon of E. coli produce

Answer 37

3 - all needed for use of lactose

Question 38

what is the main energy source for E. coli and most organisms

Answer 38

glucose

Question 39

what is glucose metabolized by

Answer 39

glycolysis pathway

Question 40

lactose

Answer 40

one of many sugars that can serve as an alternate carbon source - utilization controlled by lac operon

Question 41

lactose is a disaccharide of __________ and __________

Answer 41

glucose and galactose

Question 42

in lactose, what are glucose and galactose joined by

Answer 42

covalent B-galactoside linkage

Question 43

bacteria with a lac+ phenotype can grow on media containing what?

Answer 43

lactose as the only sugar

Question 44

can bacteria with the lac- phenotype utilize lactose?

Answer 44

no

Question 45

how can lac+ bacteria grow on lactose

Answer 45

produce gated channel (permease) at cell membrane that allows lactose to enter the cell and the enzyme B-galactosidase to break the B-galactoside linkage

Question 46

glucose produced by lactose breakdown enters _________

Answer 46

glycolysis

Question 47

galactose is processed to produce _________

Answer 47

glucose

Question 48

the breakdown of lactose produces a small amount of _________

Answer 48

allolactose

Question 49

what does allolactose act as

Answer 49

inducer compound

Question 50

3 binding sites of lac regulatory region

Answer 50

1. promoter - binds RNA polymerase 2. operator - binds lac repressor protein 3. CAP binding site

Question 51

3 operon structural genes of lac

Answer 51

1. lac Z 2. lac Y 3. lac A

Question 52

what does lacZ encode

Answer 52

B-galactosidase - cleaves lactose into glucose and galactose

Question 53

what does lacY encode

Answer 53

permease - helps transport lactose into the cell

Question 54

what does lacA encode

Answer 54

transacetylase - precise function is mystery

Question 55

how are lac Z, Y, and A transcribed

Answer 55

as single, polycistronic mRNA, which is translated to produce the 3 distinct polypeptides

Question 56

what gene is next to the lac operon?

Answer 56

lacI

Question 57

is lacI part of the lac operon?

Answer 57

no

Question 58

is lacI constitutively or inducible expressed

Answer 58

constitutively

Question 59

what does lacI encode

Answer 59

the lac repressor protein

Question 60

lac repressor protein

Answer 60

- homo-tetramer - DNA-binding domain that binds to the lacO sequence (operator) - has allosteric domain that binds to the inducer (allolactose)

Question 61

what is present even when lactose is absent?

Answer 61

a very low basal level of transcriptional from the operon

Question 62

how is there always a small amount of transcription for the lac operon

Answer 62

small amount of permeate and B-galactosidase proteins allow for the import of lactose into a cell and production of allolactose

Question 63

what happens when there are no or low levels of B-galactosidase

Answer 63

no allolactose in the cell, lac repressor protein binds to lacO and prevents transcription