Today: Regulating gene expression in bactriaExam #1 T 2/17 in class

Available:F and M 10-11am, noon-2pm, after 3pmT after 2pm

Combinations of 3 nucleotides code for each 1 amino acid in a protein.

We looked at the mechanisms of gene expression, now we will look at its regulation.

Why change gene expression?

•Different cells need different components•Responding to the environment•Replacement of damaged/worn-out parts

Fig 15.1

Two points to keep in mind:

1. Cellular components are constantly turned-over.

2. Gene expression takes time:

Typically more than an hour from DNA to protein. Most rapidly 15 minutes.

Fig 15.1

•Gene expression can be controlled at many points between DNA and making the final proteins.

•Changes in the various steps of gene expression control when and how much of a product are produced.

Fig 15.1

Blood clotting must happen within minutes

Fowler and ThomashowThe Plant Cell, Vol. 14, 1675-1690, 2002

mRNA levels change in response to cold acclimation

Fig 1b

DNA damage inhibits rRNA transciption

The ATM repair pathway inhibits RNA polymerase I transcription in response to chromosome breaksNature Vol 447 pg 730-734 (7 June 2007)

•Gene expression can be controlled at many points between DNA and making the final proteins.

•Changes in the various steps of gene expression control when and how much of a product are produced.

Fig 15.1

In bacteria, transcription and translation occur simultaneously. So most regulation of gene expression happens at transcription.

Fig 13.22

Transcription initiation in prokaryotes:sigma factor binds to the -35 and -10 regions and then

the RNA polymerase subunits bind and begin transcription Fig 12.7

Fig 14.3

Operon: several genes whose expression is controlled by the same promoter

Fig 14.3E. coli lactose metabolism

Fig 14.4 In the absence of lactose, the lac operon is repressed.

Fig 14.4 Lactose binds to the repressor, making it inactive, so that transcription can occur.

Fig 14.5

Repression or induction of the lac operon

Fig 14.3 There is more to lac gene expression than repression

Fig 14.8 Glucose is a better energy source than lactose

Fig 14.8 Low glucose leads to high cAMP

cAMP binds to CAP which increases lac operon transcription

Fig 14.8High glucose leads to low cAMP

low cAMP, CAP inactive, low lac operon transcription

Fig 14.3

The lac operon: one example of regulating gene expression in bacteria

The ara Operon products metabolize arabinose (a sugar)

In the absence of arabinose, the araC protein inhibits the expression of the ara operon.

Fig 14.12

With arabinose, the araC protein activates transcription.

Fig 14.12

The expression of micF inhibits the ompF gene at high osmolarity

micF RNA does not code for a protein It is antisense RNA

Fig 14.16

If the concentration of product 3 becomes high, it binds to enzyme 1

Thereby inhibiting its ability to convert substrate 1 into product 1

Feedback inhibition

*This mechanism regulates the production of cysteine in E. coli

In bacteria, transcription and translation occur simultaneously. So most regulation of gene

expression happens at transcription, but not all.

Fig 13.22