ADL Lecture 3: 14.1-3

Question 1

Constitutive transcription

Answer 1

state in which a gene is continuously transcribed (in bacteria, some genes need to be Constitutively transcribed in order to perform certain tasks)

Question 2

regulated transcription

Answer 2

condition in which gene expression is controlled at the transcriptional level in response to changing environmental conditions. (controls initiation/amount of transcription) most regulation of gene expression in bacteria is regulated trans.

Question 3

negative control of gene transcription

Answer 3

binding of a repressor protein to reg. DNA to prevent transcription

Question 4

positive control of gene transcription

Answer 4

binding of activator protein to reg. DNA sequence to initiate transcription

Question 5

Repressor proteins

Answer 5

• exert neg. control of transcription

- can be activated/inactivated via interactions with other compounds

Question 6

Binding of repressor protein to DNA sequence results in…

Answer 6

no transcription

Question 7

Binding of inducer molecule to repressor protein results in…

Answer 7

transcription

Question 8

binding of repressor-corepressor complex results in…

Answer 8

no transcription

Question 9

with corepressor absent, the repressor protein…

Answer 9

does not bind to DNA sequence and allows transcriptions

Question 10

Activator proteins

Answer 10

bind to regulatory DNA sequences and help initiate transcription

Question 11

Absence of the allosteric effetor compound… (results in what? in relation to activator proteins)

Answer 11

prevents activator protein binding and inhibits transcription

Question 12

Effector binding to activator protein…

Answer 12

facilitates RNA polymerase binding at promoters helps initate transcription

Question 13

Binding of the allosteric inhibitor compound to the activator protein…

Answer 13

prevents activtor protein binding/transcription

Question 14

absence of an inhibitor molecule (in relation to an activator protein)

Answer 14

allos binding of activator protein and transcription

Question 15

What are the two active sites in repressor proteins and what do they do?

Answer 15

1. DNA-binding domain: responsible for finding/binding operator DNA sequence/target regulatory sequences
2. Allosteric domain: binds molecule or protein-causing change in shape of DNA-binding site

Question 16

lacl
Function:
Product type:

Answer 16

1. contains two binding sites, one for operator and one for lactose, the inducer (continuously expressed)
2. repressor protein

Question 17

lacZ
Function:
product type:

Answer 17

1. Cleaves lactose into 2 monosaccharides (glucose/galactose)
2. B-galactosidase

Question 18

lacY
function:
product type:

Answer 18

1. facilitates lactose transport across cell membrane

2. permease

Question 19

lacA
function:
product type:

Answer 19

1. protects against harmful by-products of lactose metabolism
2. transacetylase

Question 20

lacO
function:
product type:

Answer 20

1. binds repressor protein to block transcription of operon genes
2. operator

Question 21

lacP
function:
product type:

Answer 21

1. binds RNA polymerase

2. promoter

Question 22

operons

Answer 22

clusters of genes undergoing coordinated transcriptional regulation by shared regulatory region (common in bacterial genomes-genes participate in same metabolic/biosynthesis pathway)

Question 23

lactose (lac) operon

Answer 23

responsible for producing three polypeptides needed for lactose

Question 24

lactose metabolism

Answer 24

enzyme B-galactosidase cleaves B-galactoside linkage of disaccharide lactose and yeilds monosaccharides of glucose and galactose

Question 25

Which monosaccaride is the preferred source of energy for E. Coli? and what biochemical pathway is it metabolized by?

Answer 25

glucose; glycolsis

Question 26

inducible systems

Answer 26

turned on only when an inducer compound is avaiable

Question 27

What sugar can serve as an alternate carbon source?

Answer 27

lactose

Question 28

lac+ phenotype vs lac- phenotype

Answer 28

lac + able to grow on medium containing lactose as only sugar lac- unable to grow on a loctose-containing medium

Question 29

allolactose

Answer 29

acts as inducer compound; alternate form of lactose

Question 30

Describe the lac operon structure

Answer 30

1. has multipart regulatory region (promoter-binds RNA pol; lacO-binds repressor protein; CAP-cAMP region; all partially overlap) 2. three structural genes

Question 31

polycistronic mRNA

Answer 31

translated to produce three distinct polypeptides

Question 32

Describe (in order) the sequences/sites of the promoter region, regulatory region and the lactose operon region

Answer 32

Short: lacl promoter; lacl; CAP site; lacP; lacO; lacZ; lacY; lacA 1. Promoter region: (within regulatory region) CAP site; lacP; lacO 2. Regulatory region: same as promoter region except is contains a lacl gene before the CAP site and a lacZ gene after the operator 3. The lactose operon contains the regulatory region in additoin to the lacY and lacA genes immediately following

Question 33

Lac operon function

Answer 33

1. when lactose is unavailable and glucose is availabe- transcription in inhibited lac repressor protein binds to lacO (negative control) 2. when lactose is availabe and glucose in unavailabe- transcription is carried out (repressor protein inactivated by allolactose binding--prevents binding to lacO- inducer-repressor complex)

Question 34

Is cAMP increase or decreases during glycolysis and what is the result?

Answer 34

cAMP is decreased; CAP-cAMP complex cannot form; makes transcription inefficient -- called catabolite repression

Question 35

If lacZ and lacY are wild-type/trans-heterozygotes under lactose induction, what doe this tell yoiu?

Answer 35

That the two mutations complement one another

Question 36

constitutive mutants

Answer 36

transcribed continuously whether or not lactose is availabe

Question 37

lacl+ (wild-type) vs lacl- (repressor mutation- mutation in DNA binding domain)

Answer 37

lacl+ : reprossor binds to lacO when inducer is absent/ doesn't bind to lacO when inducer-repressor complex is formed lacl- : prevents binding to lacO; produces conotinuous synthesis of lac operon

Question 38

lacO^c (operator constitutive mutation)

Answer 38

prevents repressor protein binding; produces continuous synthesis of lac operon

Question 39

lacI^s (super-repressor mutation)

Answer 39

repressor protein mutation blocks binding to inducer; preventing formation of complex; mutated protein binds to lacO which inhibts transcription (genes are unresponsive in presence of lactose)

Question 40

what is the result if lacP is mutated?

Answer 40

reduced/eliminated transcription

Question 41

Why is the lac operon ON only when glucose is absent and lactose is present?

Answer 41

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Question 42

If bacteria were diploids what would be the effect of the different lac mutations as heterozygotes in against a wild-type allele?

Answer 42

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