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Transcript
Chapter 18
Genetics of Viruses and Bacteria
Gene
Regulation
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
High levels of tryptophan inhibits the
first enzyme in the process that makes
more tryptophan.
Gene Regulation
This is negative feedback.
Gene Regulation
This is negative feedback.
Making tryptophan
Gene Regulation
This is negative feedback.
Making tryptophan
means
we
have
more
Gene Regulation
This is negative feedback.
which inhibits
Making tryptophan
means
we
have
more
Gene Regulation
This is negative feedback.
which inhibits
Making tryptophan
means
we
have
more
Gene Regulation
Negative feedback is also used to
regulate the genes that make the five
enzymes that make tryptophan.
A
B
C
D
E
Gene Regulation
DNA codes for these enzymes.
======================EDCBA=====
Gene Regulation
RNA polymerase has to attach to the
DNA to start transcription of the genes.
======================EDCBA=====
Gene Regulation
It needs a place to attach.
The promoter is a region of DNA that
marks the beginning of the gene.
======================EDCBA=====
Gene Regulation
It needs a place to attach.
The promoter is a region of DNA that
marks the beginning of the gene.
======================EDCBA=====
Gene Regulation
It needs a place to attach.
The promoter is a region of DNA that
marks the beginning of the gene.
======================EDCBA=====
Gene Regulation
RNA polymerase makes the mRNA for
the five enzymes.
======================EDCBA=====
EDCBA
Gene Regulation
The mRNA goes to the ribosomes where
the five enzymes are made.
======================EDCBA=====
ABCDE
Gene Regulation
The five enzymes make tryptophan.
======================EDCBA=====
Gene Regulation
When there is enough tryptophan, the
first enzyme is inhibited.
======================EDCBA=====
Gene Regulation
But the genes could still go on making
more enzymes.
======================EDCBA=====
Gene Regulation
But the genes could still go on making
more enzymes.
======================EDCBA=====
ABCDE
Gene Regulation
But the genes could still go on making
more enzymes.
======================EDCBA=====
ABCDE
Gene Regulation
But the genes could still go on making
more enzymes.
======================EDCBA=====
Gene Regulation
But the genes could still go on making
more enzymes.
======================EDCBA=====
ABCDE
Gene Regulation
But the genes could still go on making
more enzymes.
======================EDCBA=====
ABCDE
Gene Regulation
You really don’t need all those enzymes
if you’re not using them.
======================EDCBA=====
Gene Regulation
You want to be able to shut off the gene.
Actually, you want to shut off all 5 genes.
======================EDCBA=====
Gene Regulation
The repressor gene trpR makes a
repressor molecule.
==trpR================EDCBA=====
Gene Regulation
The repressor gene trpR makes a
repressor molecule.
==trpR================EDCBA=====
Gene Regulation
The repressor gene trpR makes a
repressor molecule.
==trpR================EDCBA=====
Gene Regulation
The repressor gene trpR makes a
repressor molecule.
==trpR================EDCBA=====
trpR
Gene Regulation
The repressor gene trpR makes a
repressor molecule.
==trpR================EDCBA=====
trpR
Gene Regulation
The repressor gene trpR makes a
repressor molecule.
==trpR================EDCBA=====
trpR
Gene Regulation
The repressor is inactive.
==trpR================EDCBA=====
Gene Regulation
It needs tryptophan to be a corepressor
in order to activate it.
==trpR================EDCBA=====
Gene Regulation
When there is a lot of tryptophan,
enough repressor is activated to shut
down the gene.
==trpR================EDCBA=====
Gene Regulation
The activated repressor binds to the
operator region inside the promoter.
==trpR================EDCBA=====
Gene Regulation
This prevents RNA polymerase from
binding to DNA.
==trpR================EDCBA=====
Gene Regulation
This prevents RNA polymerase from
binding to DNA.
==trpR================EDCBA=====
Gene Regulation
This prevents RNA polymerase from
binding to DNA.
==trpR================EDCBA=====
Gene Regulation
The operon includes the promoter,
operator, and all five genes.
==trpR================EDCBA=====
Gene Regulation
The regulatory gene is separate.
==trpR================EDCBA=====
Gene Regulation
The repressor is inactive
==trpR================EDCBA=====
Gene Regulation
The repressor is inactive
until the corepressor binds to it.
==trpR================EDCBA=====
Gene Regulation
The genes that make tryptophan are
repressible genes.
==trpR================EDCBA=====
Positive Feedback
Positive Feedback
E. coli needs three separate enzymes to
digest lactose.
Positive Feedback
Tryptophan was something the cell
needed to make, so the trp gene was
repressed by tryptophan.
Positive Feedback
Lactose is something the cell needs to
digest, so the lac gene is induced by
lactose.
Positive Feedback
The lac genes are inducible genes.
=========== lacL ======ZYA========
Positive Feedback
The regulatory gene, lacL, makes an
active repressor.
=========== lacL ======ZYA========
Positive Feedback
The repressor binds to the operator
region within the promoter.
=========== lacL ======ZYA========
=
Positive Feedback
RNA polymerase is blocked from
transcribing the structural genes.
=========== lacL ======ZYA========
Positive Feedback
Lactose is an inducer.
=========== lacL ======ZYA========
Positive Feedback
It inactivates the repressor.
=========== lacL ======ZYA========
Positive Feedback
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========