Lecture 11 - gene regulation in bacteria

Question 1

what is the difference in size of eukaryotes compared to prokaryotic bacterial cells?

Answer 1

most bacterial cells are 0.5-5um, compared to 10-100um eukaryotes.

Question 2

what are the three major bacterial morphologies?

Answer 2

> spherical (cocci)
rod-shaped (bacilli)
spiral

Question 3

what is a consequence of bacteria not having a nucleus?

Answer 3

transcription and translation both occur in the cytoplasm.

Question 4

what is the size of a bacterial genome?

Answer 4

approx. 2500 to 6000 genes, depending on how big the genome is.

Question 5

how do bacteria respond to environmental change?

Answer 5

they regulate their gene expression.
>for example E.coli can tune its metabolism to changes in the environment and different food sources in order to outcompete other bacteria and survive.

Question 6

how do bacteria respond to environmental change?

Answer 6

they regulate their gene expression.
>for example E.coli can tune its metabolism to changes in the environment and different food sources in order to outcompete other bacteria and survive.

Question 7

what is the molecular anatomy of a bacteria gene?

Answer 7

> bacterial transcription is regulated by a single RNA polymerase
RNA poly: - 5 core subunits and a regulatory sigma subunit
sigma subunit required for correct initiation of transcription (recognises promoter sequence in bacterial genes.)
RNA pol will be recruited to the promoter region of a gene by the binding of a sigma factor.

Question 8

what is an operon?

Answer 8

> an operon is a unit of genetic function. it consists of a coordinately regulated cluster of genes with a relates function.
in bacteria, genes are often clustered into operons composed of:
- an operator, an “on-off” switch
- a promoter
- genes for the proteins that work together
the genes within an operon can be switched “on” and “off” by regulatory proteins.

Question 9

what is an operon?

Answer 9

> an operon is a unit of genetic function. it consists of a coordinately regulated cluster of genes with a relates function.
in bacteria, genes are often clustered into operons composed of:
- an operator, an “on-off” switch
- a promoter
- genes for the proteins that work together
the genes within an operon can be switched “on” and “off” by regulatory proteins.

Question 10

what is in the region of transcriptional control?

Answer 10

the promoter and operator.

Question 11

what is a promoter?

Answer 11

specific DNA sequence recognised by RNA polymerase. RNA polymerase binds to the promoter and transcription is initiated.

Question 12

what is an operator?

Answer 12

specific DNA sequence which binds with the corresponding regulatory protein. This regulator-operator complex can ‘turn a gene on or off’ by interfering with RNA polymerase activity.

Question 13

what is an operator?

Answer 13

specific DNA sequence which binds with the corresponding regulatory protein. This regulator-operator complex can ‘turn a gene on or off’ by interfering with RNA polymerase activity.

Question 14

know how E.coli self regulates the expression of lactose metabolising enzymes .

Answer 14

1) when there is no lactose present, the LacI repressor and gene is always transcribed, then binding to the operator sequence of the lactose enzymes, thus blocking RNA polymerase - therefore no lactose metabolising proteins are transcribed.
2) if lactose is present, then it acts as an inducer itself. its isomer, allolactose, binds to the repressor protein, LacI, this changes its confirmation and it can therefore not bond to the operator, therefore the lactose enzymes ARE transcribed.

3)

Question 15

know how E.coli self regulates the expression of lactose metabolising enzymes .

Answer 15

1) when there is no lactose present, the LacI repressor and gene is always transcribed, then binding to the operator sequence of the lactose enzymes, thus blocking RNA polymerase - therefore no lactose metabolising proteins are transcribed.
2) if lactose is present, then it acts as an inducer itself. its isomer, allolactose, binds to the repressor protein, LacI, this changes its confirmation and it can therefore not bond to the operator, therefore the lactose enzymes ARE transcribed.
3) low glucose levels result in high levels of cyclic AMP. cyclic AMP binds to CAP, activating it. Active AMP binds to the activator region of DNA, increasing RNA polymerase activity. Therefore a shit ton of Lactose enzymes are produced.
4) when glucose levels increase, CAP detaches from the lac operon, reducing transcription. high glucose = low AMP. thus AMP not likely to bind to CAP, therfore little active CAP, thus RNA pol activity remains low.

Question 16

know how E.coli self regulates the expression of lactose metabolising enzymes .

Answer 16

1) when there is no lactose present, the LacI repressor and gene is always transcribed, then binding to the operator sequence of the lactose enzymes, thus blocking RNA polymerase - therefore no lactose metabolising proteins are transcribed.
2) if lactose is present, then it acts as an inducer itself. its isomer, allolactose, binds to the repressor protein, LacI, this changes its confirmation and it can therefore not bond to the operator, therefore the lactose enzymes ARE transcribed.
3) low glucose levels result in high levels of cyclic AMP. cyclic AMP binds to CAP, activating it. Active AMP binds to the activator region of DNA, increasing RNA polymerase activity. Therefore a shit ton of Lactose enzymes are produced.
4) when glucose levels increase, CAP detaches from the lac operon, reducing transcription. high glucose = low AMP. thus AMP not likely to bind to CAP, therfore little active CAP, thus RNA pol activity remains low.

Question 17

what happens in Trytophan synthesis and regulation?

Answer 17

1) 5 enzymes are required for Trytophan synthesis. Trytophan inhibits both an enzyme in the pathway and the expression of the genes encoding the enzymes.
2) Tryptophan absent, repressor inactive, operon “on”

Question 18

what happens in Trytophan synthesis and regulation?

Answer 18

1) 5 enzymes are required for Trytophan synthesis. Trytophan inhibits both an enzyme in the pathway and the expression of the genes encoding the enzymes.
2) Tryptophan absent, repressor inactive, operon “on”

3)

Question 19

know how E.coli self regulates the expression of lactose metabolising enzymes .

Answer 19

1) when there is no lactose present, the LacI repressor and gene is always transcribed, then binding to the operator sequence of the lactose enzymes, thus blocking RNA polymerase - therefore no lactose metabolising proteins are transcribed.
2) if lactose is present, then it acts as an inducer itself. its isomer, allolactose, binds to the repressor protein, LacI, this changes its confirmation and it can therefore not bond to the operator, therefore the lactose enzymes ARE transcribed.
3) low glucose levels result in high levels of cyclic AMP. cyclic AMP binds to CAP, activating it. Active AMP binds to the activator region of DNA, increasing RNA polymerase activity. Therefore a shit ton of Lactose enzymes are produced.
4) when glucose levels increase, CAP detaches from the lac operon, reducing transcription. high glucose = low AMP. thus AMP not likely to bind to CAP, therefore little active CAP, thus RNA pol activity remains low.

Question 20

what happens in Tryptophan synthesis and regulation?

Answer 20

1) 5 enzymes are required for Tryptophan synthesis. Tryptophan inhibits both an enzyme in the pathway and the expression of the genes encoding the enzymes.
2) Tryptophan absent, repressor inactive, operon “on”
3) tryptophan present, repressor now active, operon not transcribed

Question 21

what is the co-ordinate control of Trp Operon?

Answer 21

> by default the trp operon is on and the genes for tryptophan synthesis are transcribed
when tryptophan is present, it binds to the trp repressor protein, which turns the operon off.
the repressor is active only in the presence of its corepressor tryptophan; thus the trp operon is turned off (repressed) if tryptophan levels are high.