Exam 3 - Lecture 15

Question 1

what are the two approaches to protein regulation?

Answer 1

• regulation of gene expression (transcription/translation)
• alter activity of enzymes and proteins (posttranslational)

Question 2

how is transcription regulated? what kind of genes allow for this regulation?

Answer 2

genes aren’t expressed all the time
- constitutive/housekeeping genes
- inducible genes
- repressible genes

Question 3

what are inducible genes and what pathways do their enzymes function in?

Answer 3

• genes that are usually off but can be turned on
• function in catabolic pathways

Question 4

what are repressible genes and what pathways do their enzymes function in?

Answer 4

• genes that are usually on but can be turned off
• function in anabolic pathways

Question 5

what reaction does beta-galactosidase catalyze?

Answer 5

hydrolysis of lactose into galactose and glucose

Question 6

is the beta-galactosidase gene inducible or repressible? is it on or off in the presence of lactose?

Answer 6

• inducible gene
• only turned on in the presence of lactose

Question 7

inducible enzymes are only present when their _________ is available

Answer 7

substrate

Question 8

repressible genes are present unless the _____ _________ of the biosynthetic pathway is available

Answer 8

• end product
• (no need to make more of the product if it’s available)

Question 9

induction and repression occur due to activity of regulatory proteins containing _____ _________ __________

Answer 9

DNA binding domains

Question 10

what is negative transcriptional control?

Answer 10

binding of a regulatory protein (repressor) at the DNA regulatory site (operator) inhibiting initiation of transcription

Question 11

true or false: repressor proteins can exist in both active and inactive forms

Answer 11

true

Question 12

what two molecules can alter the activity of repressors?

Answer 12

inducers and corepressors

Question 13

a repressor is bound to the operator. an inducer binds the repressor, causing it to detach from the operator.

does transcription occur? what kind of regulation is this?

Answer 13

• yes, transcription occurs
• negative control of an inducible gene

Question 14

a repressor is not bound to the operator. a corepressor binds the repressor, causing it to attach to the operator.

does transcription occur? what kind of regulation is this?

Answer 14

• no, transcription stops
• negative control of a repressible gene

Question 15

what is positive transcriptional control?

Answer 15

when an activator promotes transcription

Question 16

an activator is not bound to the operator. an inducer binds the activator, causing it to attach to the operator.

does transcription occur? what kind of regulation is this?

Answer 16

• yes, transcription occurs
• positive control of an inducible gene

Question 17

an activator is bound to the operator. an inhibitor binds the activator, causing it to detach from the operator.

does transcription occur? what kind of regulation is this?

Answer 17

• no, transcription does not occur
• positive control of a repressible gene

Question 18

what represses lactose metabolism in the Lac operon?

Answer 18

• LacI repressor

Question 19

what are the three structural genes coding for lactose uptake and metabolism?

Answer 19

lacZ, lacY, and lacA

Question 20

what are the three operator binding sites for LacI tetramers? how does LacI bind?

Answer 20

• O1, O2, and O3
• binds TWO of the three sites; (always binds O1) O1 and O2 or O1 and O3

Question 21

how does LacI block RNA polymerase from binding?

Answer 21

• it bends the DNA which blocks RNA pol from binding the operator

Question 22

what binds the LacI repressor causing it to no longer bind to the operator?

Answer 22

allolactose

Question 23

in the absence of lactose, does LacI bind to the operator?

Answer 23

yes

Question 24

in the presence of lactose, does LacI bind to the operator?

Answer 24

no

Question 25

what is the protein that positively regulates the lac operon?

Answer 25

catabolite activator protein (CAP)

Question 26

CAP regulates the lac operon in response to the presence or absence of _________

Answer 26

glucose

Question 27

do cells prefer lactose or glucose?

Answer 27

glucose

Question 28

when glucose if present, will the lac operon be activated?

Answer 28

no; the cells prefer glucose and don't need to use lactose

Question 29

what are the two conditions required for activation of lac operon?

Answer 29

- absence of (or low) glucose - presence of (or high) lactose

Question 30

the Tryptophan (trp) operon only functions in the _________ of tryptophan

Answer 30

absence

Question 31

what kind of control does the trp repressor do for the trp operon?

Answer 31

negative control

Question 32

how many structural proteins does the trp operon code for?

Answer 32

5

Question 33

what is attenuation (in the trp operon)? what structures allow for this to occur?

Answer 33

- the termination of transcription within the leader region, ending transcription before the gene is transcribed - occurs through stem-loop structures in the mRNA depending on the levels of trp present

Question 34

the trp leader sequence contains a short peptide called:

Answer 34

TrpL

Question 35

if the amount of charged Trp tRNA is low, does transcription stop or continue? where does the antiterminator loop form on the trp mRNA?

Answer 35

- it continues - antiterminator: regions 2 & 3

Question 36

what two regions on the trp mRNA form the transcription terminator?

Answer 36

regions 3 & 4

Question 37

riboswitches are a specialized form of transcription ____________

Answer 37

attenuation

Question 38

what does folding of the mRNA leader sequence (riboswitch) determine?

Answer 38

whether transcription will continue or terminate

Question 39

binding of what alters the folding response of the riboswitch?

Answer 39

an effector molecule to the mRNA

Question 40

what is a regulon?

Answer 40

a set of genes or operons controlled by a common regulatory protein

Question 41

what is an example of a global regulator in the lac operon?

Answer 41

CAP

Question 42

many genes and operons are turned on or off in response to:

Answer 42

environmental conditions

Question 43

what are four regulation mechanisms global regulatory systems often use? which is the most common*?

Answer 43

- two component signal transduction systems* - phosphorelay systems - regulatory systems - alternative sigma factors

Question 44

how many domains of life are two component regulatory systems found in?

Answer 44

all three

Question 45

what are the two proteins found in the two component regulatory system?

Answer 45

- sensor kinase (histidine kinase) - response-regulator protein

Question 46

what are the characteristics of sensor kinase (histidine kinase)?

Answer 46

- extracellular receptor for sensing - intracellular communication domain

Question 47

what are the characteristics of the response-regulator protein?

Answer 47

- intracellular protein - activated by sensor kinase - DNA binding protein (activator/repressor)

Question 48

activation of ________ ________ results in the phosphorylation of its histidine

Answer 48

sensor kinase

Question 49

the ___________-__________ ________ is activated by sensor kinase

Answer 49

response-regulator protein

Question 50

when the response-regulator protein is activated, a phosphate group is transferred from _____ to _____

Answer 50

His to Asp

Question 51

EnvZ is a _________ ________ that phosphorylates in ______ osmolarity

Answer 51

sensor kinase; high osmolarity

Question 52

OmpR is a ___________ __________ that regulates transcription when phosphorylated

Answer 52

response regulator

Question 53

expression of what two outer membrane proteins do OmpR and EnvZ regulate? what is their regulation dependent on?

Answer 53

- OmpC and OmpF - depends of osmolarity

Question 54

match the following: 1. OmpF 2. OmpC a. dominant when E. coli is in high osmolarity b. dominant when E. coli is in dilute environment

Answer 54

1b. OmpF: dominant when E. coli is in dilute environment 2a. OmpC: dominant when E. coli is in high osmolarity

Question 55

which is usually the protein that is on: OmpF or OmpC?

Answer 55

OmpF

Question 56

match the following: 1. OmpR represses 2. OmpR activates a. ompF b. ompC

Answer 56

1a: OmpR represses ompF 2b: OmpR activates ompC