Transcript regulatory gene

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Operon
◦ Inducible and
repressible
Promoter
Terminator
Enhancer
Regulatory Gene
Inducer
Repressor
Regulatory
Protein/Sequence
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Positive gene control
Negative gene control
Lac Operon
Trp Operon
Plasmid
Transformation
Conjugation
Retrovirus
Lytic cycle
Lysogenic cycle
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operator: “switch” that controls access of RNA
polymerase to genes for transcription
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repressor: a protein that binds to the operator to
block transcription
◦ corepressor: small molecule that binds to repressor to make
it active (helps block transcription)
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regulatory gene: gene that code for the production
of repressors (always on at a low rate)
Regulatory sequence: stretch of DNA that interacts
with regulatory proteins to control transcription
(promoter, terminator, enhancer)
inducer: small molecule that inactivates the
repressor (allows transcription)
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Chapters 18, 19, and 20
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Genes regulated at the transcription stage
(mostly).
◦ feedback inhibition (positive and negative)
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Important in embryonic development
(eukaryotes) to create differentiated cells
Also important in cancer prevention and
regulation of the cell cycle
There are differences in the way prokaryotes and
eukaryotes regulate gene expression…why??
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Express only those genes that are needed by
the cell (allows for efficient metabolism)
◦ Adjust activity of enzymes
◦ Adjust production level of enzymes
 Genes switched on/off as needed due to environmental
conditions
◦ Operon model: basic mechanism for the control of
gene expression in bacteria
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Operon: entire stretch of DNA required to
produce a protein (enzyme)—under the
control of a single promoter
◦ this may include several genes
 operator + promoter + genes
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Negative Gene Regulation (operon switched
off by repressor)
◦ Lac operon (inducible)
◦ Trp operon (repressible)
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inducible operon. usually “off” but can be
turned on by allolactose (sugar--isomer of
lactose)
◦ inactivates repressor to allow for transcription
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genes code for 3 enzymes that utilize lactose
 Figures 18.4(a) and 18.4(b)
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repressible operon. controls synthesis of
tryptophan (amino acid)
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is usually “on”, but can be switched off by a
repressor. (prevents transcription)
◦ controlled by a regulatory gene (trpR). (always
expressed at a low rate)
 allosteric regulation!
 Increased concentration of tryptophan will result in less
of it synthesized by bacteria
 Figures 18.3(a) and 18.3(b)
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Positive gene regulation (regulatory protein interacts
directly with genome to switch transcription on)
 Positive feedback!
◦ Cyclic AMP (cAMP) and Lac operon
 bacteria preferentially use glucose for energy
(glycolysis) but will use lactose in its absence (lac
operon switches on)
 cAMP accumulates when glucose is scarce
 enhances the production of enzymes from the lac
operon (directly stimulates gene expression)
 Binds to specific region in promoter
 also has the ability to enhance the transcription of
other genes (not just lac)
Three shapes (cocci, bacilli, spirilla)
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Gram+ and Gram◦ Cell wall type
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lack complex compartmentalization (prokaryotes)
◦ circular chromosome located in nucleoid (region of
cytoplasm)
◦ Plasmids (independently replicating DNA carrying
few genes)
 R plasmid (carries resistance genes for specific
antibiotics)
-MRSA (methicillin
resitance)
-Multi-drug resistant
strains
-Enterococcus sp.
-Pseudomonas sp.
-Tuberculosis
Implications for human
and veterinary medicine,
as well as agriculture
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No sexual reproduction
◦ asexual (binary fission)
New mutations increase genetic diversity rapidly
due to short generation times (rapid evolution)
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Horizontal Gene Transfer…
◦ Transformation (take in foreign DNA from its
surroundings)
 produces recombinant cells (DNA from two different
cells)
◦ Transduction (bacteriophages--viruses carry genes
from one cell to another)
 recombinant cells produced
◦ Conjugation (DNA transferred between two cells--one
cell donates the other receives)
◦ Transposition (DNA segments move with and
between molecules)
 “jumping genes”—move from chromosome to plasmid
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No Operons!!
Differential gene expression: different genes
expressed by cells within the same genome
◦ Depends on cell function or stage of development
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Like prokaryotes, most often regulated at the
stage of transcription (but much more
complex)
◦ Eukaryotes do have the ability to control gene
expression at every step of the process
http://www.bozemanscienc
e.com/031-generegulation/
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Transcription factors need to be present for the
process to begin
◦ These bind to specific DNA sequences “upstream” of
the gene to be expressed (regulatory regions—
enhancer/promoter)
 Attracts RNA polymerase to attach
◦ Controlling availability of these factors in a cell is a
major component in regulating gene expression
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Some factors are activators (increase expression)
others are repressors (decrease expression)
◦ These determine what (or if) genes will be expressed
(and how much)
 This changes phenotype of the organism!
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Plasmids can be used to genetically engineer
organisms, also to further study specific genes
◦ Easily moved between organisms, easily manipulated
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restriction enzymes (restriction endonucleases) are
used to cut DNA at specific sequences (restriction
sites)
◦ Produces blunt or sticky ends (depends on cut)
◦ Hundreds have been identified, each recognizes a specific
site
 EcoR1 cuts at GAATTC
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DNA (cut with the same enzyme) is then
combined with other DNA making a
recombinant DNA sequence
◦ Base-pairing occurs, ligase seals break
◦ This can produce some very interesting organisms! It
allows for cells to produce proteins they wouldn’t
normally.
 Insulin, vaccines, oil spill clean up, agriculture, etc.
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