regulation of prokaryotic gene expression

Question 1

what are housekeeping genes

Answer 1

genes that are always switched on
(genes that produce proteins involved in making amino acids, transcription, translation etc)

Question 2

most regulation of gene expression in bacteria is:

Answer 2

transcriptional control - no mRNA synthesis

Question 3

negative control of transcription

Answer 3

binding of a repressor protein to a regulatory DNA sequence preventing transcription of a gene

Question 4

positive control of transcription

Answer 4

binding of an activator protein to a regulatory DNA sequence, inititiates transcription

Question 5

what is an operon

Answer 5

cluster of bacterial genes undergoing transcriptional regulation
-genes in an operon participate in the same metabolic/biosynthetic pathway

Question 6

how is lac operon an inducible operon system

Answer 6

turned on only when inducer compound is available = lactose

Question 7

lac operon - what is the structural gene region -

Answer 7

has 3 protein coding genes - lacZ, lacY, lacA

Question 8

lac operon - what is the regulatory region -

Answer 8

-CAP binding site
-promoter that binds RNA polymerase
-operator that binds lac repressor protein

Question 9

structural gene region - what do the 3 genes encode

Answer 9

1. lac Z - encodes B galactosidase, cleaves bond between lactose to form galactose and glucose
2. lac Y - encodes lactose permease - uptake of lactose from the environment
3. lac A - encodes transacetylase

3 genes transcribed as mRNA, then translated to 3 polypeptides

Question 10

lacl gene produces the ……….. protein next to the lac operon

Answer 10

lac repressor protein that then binds to the operator of lac operon and allolactose binds to it (inducer)

Question 11

breakdown of lactose produces small amount of ….. - inducer compound. slightly modified version of lactose

Answer 11

allolactose

Question 12

when there’s no lactose present - lac operon expressed at very low levels
what happens

Answer 12

lac repressor protein binds to operator (lacO) sequence inhibiting transcription

Question 13

when there’s lactose present - lac operon expressed - transcription
what happens

Answer 13

B-galactosidase produces allolactose which binds to lac repressor forming inducer-repressor complex
-repressor protein is now inactive because it is bound to allolactose so can’t bind to the operator
-RNA polymerase binds to promotor and carries out transcription

Question 14

when there’s lactose present (no glucose) - cAMP is high or low

Answer 14

high cAMP binds to CAP
CAP-CAMP then binds to the lac promoter region stimulating a high level of transcription

Question 15

when there’s no lactose present (glucose) - cAMP is high or low

Answer 15

low cAMP - prevents transcription

Question 16

mutation in lacl gene -

Answer 16

mutant lac repressor protein can’t bind to operator region
-lac operon consitutively expressed - B-galactosidase always present

Question 17

mutation in operator region (lacO) -

Answer 17

lac repressor protein can’t bind to mutated operator sequence
-lac operon constitutively expressed - B galactosidase always present

Question 18

mutation in laclS (super lac repressor)

Answer 18

mutant repressor protein cannot bind to allactose
-so binds to operator constitutively
-SO transcription never happens even when there’s lactose

Question 19

arabinose released in intestine after plant is eaten but not absorbed by intestine - it is a

Answer 19

carbon source for gut E.coli if glucose is absent

Question 20

E.coli arabinose operon - contains

Answer 20

genes required for metabolism of arabinose

Question 21

ara operon has a …. regulatory protein (araC) that carries out both positive and negative transcriptional regulation

Answer 21

single

Question 22

arabinose operon - what happens when there’s no arabinose

Answer 22

araC protein monomers bind to araI and araO2, monomers link to one another forming DNA loop
-DNA loop stops RNA polymerase and CAMP-CAP binding to promoter, so ara operon is not expressed

Question 23

arabinose operon - what happens when there is arabinose

Answer 23

arabinose breaks the connection between araC proteins at araI and araO2
-opens up DNA loop
-2nd araC-arabinose complex binds to araI and interacts with RNA pol
-CAP-CAMP binds CAP binding site - RNA pol binds to promotor and initiates transcription

Question 24

correct order of steps that can be used to identify a gene whose mutation causes a genetic disorder

Answer 24

map the mutation to the arm of a chromosome, fine map the position of the mutation using other known genetic markers on that arm, identify candidate genes, use DNA sequencing to determine mutations

Question 25

how often do E.coli replicate under optimal growing conditions

Answer 25

every 20 minutes

Question 26

genetic exchange in bacteria can be mediated by bacteriophage. what is this type of horizontal gene transfer called

Answer 26

transduction

Question 27

where does lac repressor bind

Answer 27

the operator lacO is found in the regulatory region and is where the lac repressor protein binds

Question 28

what does lacA encode

Answer 28

transacetylase

Question 29

what does lacZ encode

Answer 29

B-galactosidase

Question 30

what does lacY encode

Answer 30

lactose permease - uptake of lactose from the environment