Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
III. Allelic, Genic, and Environmental Interactions
IV. Sex Determination and Sex Linkage
V. Linkage
VI. Mutation
VII. Gene Regulation
Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
III. Allelic, Genic, and Environmental Interactions
IV. Sex Determination and Sex Linkage
V. Linkage
VI. Mutation
VII. Gene Regulation
A. Overview
All cells in an organism contain the same genetic information; the key to tissue
specialization is gene regulation – reading some genes in some cells and other
genes in other cells.
VII. Gene Regulation
A. Overview
All cells in an organism contain the same genetic information; the key to tissue
specialization is gene regulation – reading some genes in some cells and other
genes in other cells.
B. Terminology
Inducers turn a gene on…
Repressors turn a gene off…
VII. Gene Regulation
C. The lac Operon in E. coli
An “operon” is a region of genes that
are regulated as a unit – it typically
encodes > 1 protein involved in a
particular metabolic pathway.
VII. Gene Regulation
C. The lac Operon in E. coli
When lactose is present, E. coli produce three enzymes involved in lactose
metabolism. Lactose is broken into glucose and galactose, and galactose is
modified into glucose, too. Glucose is then metabolized in aerobic respiration
pathways to harvest energy (ATP). When lactose is absent, E. coli does not
make these enzymes and saves energy and amino acids.
How do these little bacteria KNOW? : )
VII. Gene Regulation
C. The lac Operon in E. coli
Lac Y - permease – increases absorption of lactose
Lac Z – B-galactosidase – cleaves lactose into glucose and galactose
Lac A – transacetylase – may code for enzymes that detoxify waste products of
lactose metabolism.
VII. Gene Regulation
C. The lac Operon in E. coli
1960 – Jacob and Monod proposed that this was an inducible system
under negative control. (Because the presence of the substrate INDUCES
transcription by SHUTTING OFF regulation).
Repressor
Gene
Repressor
Operator
RNA Poly
VII. Gene Regulation
C. The lac Operon in E. coli
1960 – Jacob and Monod proposed that this was an inducible system
under negative control. (Because the presence of the substrate INDUCES
transcription by SHUTTING OFF regulation).
LACTOSE
VII. Gene Regulation
C. The lac Operon in E. coli
The binding of lactose changes the shape of
the repressor (allosteric reaction) and it
can’t bind to the operator.
1960 – Jacob and Monod proposed that this was an inducible system
under negative control. (Because the presence of the substrate INDUCES
transcription by SHUTTING OFF regulation).
LACTOSE
VII. Gene Regulation
C. The lac Operon in E. coli
Mutant analyses confirmed these results:
VII. Gene Regulation
C. The lac Operon in E. coli
Mutant analyses confirmed these results:
VII. Gene Regulation
C. The lac Operon in E. coli
Mutant analyses confirmed these results:
VII. Gene Regulation
C. The lac Operon in E. coli
But it is even more complicated… if glucose AND lactose are present, the
operon is OFF. This is adaptive, because it’s glucose the cell needs. If
glucose is present, there is no benefit to break lactose down to get it. BUT
HOW?
VII. Gene Regulation
C. The lac Operon in E. coli
Within the promoter, there is a binding site for a Catabolic Activating Protein
– basically a “transcription factor”. CAP needs to bind in order for the RNA
Polymerase to bind. Cyclic-AMP activates CAP, causing an allosteric reaction
so it can bind the promoter.
, lactose present
VII. Gene Regulation
C. The lac Operon in E. coli
Within the promoter, there is a binding site for a Catabolic Activating Protein
– basically a “transcription factor”. CAP needs to bind in order for the RNA
Polymerase to bind. Cyclic-AMP activates CAP, causing an allosteric reaction
so it can bind the promoter. So, the binding of CAP stimulates transcription,
exerting positive control.
, lactose present
VII. Gene Regulation
C. The lac Operon in E. coli
When Glucose is present, the concentration of c-AMP declines, it does not
bind to CAP, and CAP does not bind to the Promoter; so the RNA Poly does
not bind and the genes are off.
, lactose present
VII. Gene Regulation
C. The lac Operon in E. coli
When Glucose is present, the concentration of c-AMP declines, it does not
bind to CAP, and CAP does not bind to the Promoter; so the RNA Poly does
not bind and the genes are off.
So, the lac operon is regulated first by the presence/absence of glucose; the
needed nutrient… and then by the presence of lactose, which could be
metabolized to produce glucose if necessary.
VII. Gene Regulation
C. The lac Operon in E. coli
D. Summary
These are the transcription factors that bind to enhancer and silencer regions
of the human metallothionien IIA gene promoter region!!
- What does having all these modifiers allow for?
VII. Gene Regulation
C. The lac Operon in E. coli
D. Summary
- Many proteins can be made from the same gene, by splicing the m-RNA
differently. Humans have 20-30K genes, but several 100,000 proteins!
A calcium regulator in the thyroid
A hormone made in the brain
VII. Gene Regulation
C. The lac Operon in E. coli
D. Summary
- miRNA (microRNA): quite similar, but as ss-RNA they bind m-RNA and just
stop translation. They are involved in developmental regulation .
VII. Gene Regulation
C. The lac Operon in E. coli
D. Summary
- Post-translational processing
zygote
mitosis