Chapter 18Genetics of Viruses and Bacteria

Gene Regulation

Your body needs to make tryptophan.

Gene Regulation

There are 5 steps to making tryptophan.

Gene Regulation

Eventually you have enough tryptophan.

Gene Regulation

Gene RegulationHigh levels of tryptophan inhibits the

first enzyme in the process that makes more tryptophan.

Gene RegulationThis is negative feedback.

Gene RegulationThis is negative feedback.

Making tryptophan

Gene RegulationThis is negative feedback.

means

Making tryptophan we

have

more

Gene RegulationThis is negative feedback.

which inhibits

means

Making tryptophan we

have

more

Gene RegulationThis is negative feedback.

which inhibits

means

Making tryptophan we

have

more

Gene RegulationNegative feedback is also used to regulate the genes that make the

five enzymes that make tryptophan.

A B C D E

Gene RegulationDNA codes for these enzymes.

======================EDCBA=====

Gene RegulationRNA polymerase has to attach to the DNA

to start transcription of the genes.

======================EDCBA=====

Gene RegulationIt needs a place to attach.

The promoter is a region of DNA that marks the beginning of the gene.

======================EDCBA=====

Gene RegulationIt needs a place to attach.

The promoter is a region of DNA that marks the beginning of the gene.

======================EDCBA=====

Gene RegulationIt needs a place to attach.

The promoter is a region of DNA that marks the beginning of the gene.

======================EDCBA=====

Gene RegulationRNA polymerase makes the mRNA for the five enzymes.

======================EDCBA=====

EDCBA

Gene RegulationThe mRNA goes to the ribosomes where the five enzymes are made.

======================EDCBA=====

ABCDE

Gene RegulationThe five enzymes make tryptophan.

======================EDCBA=====

Gene RegulationWhen there is enough tryptophan, the first enzyme is inhibited.

======================EDCBA=====

Gene RegulationBut the genes could still go on making more enzymes.

======================EDCBA=====

Gene RegulationBut the genes could still go on making more enzymes.

======================EDCBA=====

ABCDE

Gene RegulationBut the genes could still go on making more enzymes.

======================EDCBA=====

ABCDE

Gene RegulationBut the genes could still go on making more enzymes.

======================EDCBA=====

Gene RegulationBut the genes could still go on making more enzymes.

======================EDCBA=====

ABCDE

Gene RegulationBut the genes could still go on making more enzymes.

======================EDCBA=====

ABCDE

Gene RegulationYou really don’t need all those enzymes if you’re not

using them.

======================EDCBA=====

Gene RegulationYou want to be able to shut off the gene. Actually, you

want to shut off all 5 genes.

======================EDCBA=====

Gene RegulationThe repressor gene trpR makes a repressor molecule.

==trpR================EDCBA=====

Gene RegulationThe repressor gene trpR makes a repressor molecule.

==trpR================EDCBA=====

Gene RegulationThe repressor gene trpR makes a repressor molecule.

==trpR================EDCBA=====

Gene RegulationThe repressor gene trpR makes a repressor molecule.

==trpR================EDCBA=====

trpR

Gene RegulationThe repressor gene trpR makes a repressor molecule.

==trpR================EDCBA=====

trpR

Gene RegulationThe repressor gene trpR makes a repressor molecule.

==trpR================EDCBA=====

trpR

Gene RegulationThe repressor is inactive.

==trpR================EDCBA=====

Gene RegulationIt needs tryptophan to be a corepressor in order to activate it.

==trpR================EDCBA=====

Gene RegulationWhen there is a lot of tryptophan, enough repressor is activated to

shut down the gene.

==trpR================EDCBA=====

Gene RegulationThe activated repressor binds to the operator region inside the promoter.

==trpR================EDCBA=====

Gene RegulationThis prevents RNA polymerase from binding to DNA.

==trpR================EDCBA=====

Gene RegulationThis prevents RNA polymerase from binding to DNA.

==trpR================EDCBA=====

Gene RegulationThis prevents RNA polymerase from binding to DNA.

==trpR================EDCBA=====

Gene RegulationThe operon includes the promoter, operator, and all five genes.

==trpR================EDCBA=====

Gene RegulationThe regulatory gene is separate.

==trpR================EDCBA=====

Gene RegulationThe repressor is inactive

==trpR================EDCBA=====

Gene RegulationThe repressor is inactive

until the corepressor binds to it.

==trpR================EDCBA=====

Gene RegulationThe genes that make tryptophan are repressible genes.

==trpR================EDCBA=====

Positive Feedback

Positive FeedbackE. coli needs three separate enzymes to

digest lactose.

Positive FeedbackTryptophan was something the cell

needed to make, so the trp gene was repressed by tryptophan.

Positive FeedbackLactose is something the cell needs to digest, so the lac gene is induced by

lactose.

Positive FeedbackThe lac genes are inducible genes.

=========== lacL ======ZYA========

Positive FeedbackThe regulatory gene, lacL, makes an active repressor.

=========== lacL ======ZYA========

Positive FeedbackThe repressor binds to the operator region within the promoter.

=========== lacL ======ZYA========

=

Positive FeedbackRNA polymerase is blocked from transcribing the structural genes.

=========== lacL ======ZYA========

Positive FeedbackLactose is an inducer.

=========== lacL ======ZYA========

Positive FeedbackIt inactivates the repressor.

=========== lacL ======ZYA========

It inactivates the repressor.

=========== lacL ======ZYA========

Positive Feedback

It inactivates the repressor.

=========== lacL ======ZYA========

ZYA

Positive Feedback

It inactivates the repressor.

=========== lacL ======ZYA========

ZYA

Positive Feedback

It inactivates the repressor.

=========== lacL ======ZYA========

usable energy

Positive Feedback

But there’s more…

=========== lacL ======ZYA========

Positive Feedback

But there’s more…

If glucose is available, the cell would rather use that than lactose

=========== lacL ======ZYA========

Positive Feedback

If there is a shortage of glucose, the cell builds up quantities of cAMP.

=========== lacL ======ZYA========

Positive Feedback

cAMP is a cofactor for another regulatory protein called CRP.

(cAMP receptor protein)

=========== lacL ======ZYA========

Positive Feedback

cAMP activates CRP.

=========== lacL ======ZYA========

Positive Feedback

CRP makes the lac genes much more active.

=========== lacL ======ZYA========

Positive Feedback

So less glucose means more lactose gets digested.

=========== lacL ======ZYA========

Positive Feedback

More glucose means you don’t need to digest the lactose even if it’s there…

=========== lacL ======ZYA========

Positive Feedback

More glucose means very little cAMP.

=========== lacL ======ZYA========

Positive Feedback

Without cAMP, CRP is inactive.

=========== lacL ======ZYA========

Positive Feedback

Without CRP, the lac genes are less active.

=========== lacL ======ZYA========

Positive Feedback

Without cAMP, CRP is inactive.

=========== lacL ======ZYA========

Positive Feedback