Transcript 8.6 Gene Expression and Regulation

8.6 Gene Expression and Regulation
Activate Prior Knowledge
Humans have an estimated 20,000 to 25,000
genes.
Why wouldn’t you expect all these genes to be
transcribed and translated at the same time?
The cell would run out of energy and raw materials
(amino
acids and nucleotides). Proteins would accumulate
in the cell if they were not needed.
What might be an analogy to this in your own life?
eating all the food in the house at one time,
everyone in class speaking at once, spending
savings all at once
8.6 Gene Expression and Regulation
FLT
• Describe how prokaryotes turn genes on
and off.
• Explain how gene expression is regulated
in eukaryotic cells.
8.6 Gene Expression and Regulation
KEY CONCEPT
Gene expression is carefully regulated in both
prokaryotic and eukaryotic cells.
8.6 Gene Expression and Regulation
Prokaryotic cells turn genes on and off by controlling
transcription.
• A promotor is a DNA segment that allows a gene to be
transcribed.
• An operator is a part of DNA that turns a gene “on”
or ”off.”
• An operon includes a promoter, an operator, and one or
more structural genes that code for all the proteins needed
to do a job.
– Operons are most common in prokaryotes.
– The lac operon was one of the first examples of gene
regulation to be discovered.
– The lac operon has three genes that code for enzymes
that break down lactose.
8.6 Gene Expression and Regulation
• Power Notes
Promoter: aDNA segment that allows a gene to
be transcribed; helps RNA polymerase find
where a gene starts
Operon: a region of DNA that has promoter, an
operator, and one or more genes that code for all
the proteins needed to do a specific task;
typically found in prokaryotes
lac operon: one of the earliest operons
discovered; includes three genes involved in the
breakdown of the sugar lactose that are all under
the control of a single promoter and operator
8.6 Gene Expression and Regulation
• The lac operon acts like a switch.
– The lac operon is “off” when lactose is not present.
– The lac operon is “on” when lactose is present.
8.6 Gene Expression and Regulation
• Power Notes
Without lactose: a repressor protein is bound to the
operator and blocks RNA polymerase from transcribing
the genes (off)
With lactose: the repressor protein is bound to lactose,
which keeps it off the operator, so RNA polymerase
transcribes the genes that, in turn, break down lactose (on)
8.6 Gene Expression and Regulation
Eukaryotes regulate gene expression at many points.
• Different sets of genes are expressed in different types
of cells.
• Transcription is controlled by regulatory DNA
sequences and protein transcription factors.
8.6 Gene Expression and Regulation
• Power Notes
Controlling transcription in eukaryotic cells: transcription
is regulated at many points in eukaryotic cells; control of
the start of transcription is still an important point of
regulation; have unique combinations of regulatory DNA
sequences that are recognized by transcription factors;
some genes control the expression of other genes and
play an important role in development
8.6 Gene Expression and Regulation
• Transcription is controlled by regulatory DNA sequences
and protein transcription factors.
– Most eukaryotes have a TATA box promoter.
– Enhancers and silencers speed up or slow down the rate
of transcription.
– Each gene has a unique combination of regulatory
sequences.
8.6 Gene Expression and Regulation
• RNA processing is also an important part of gene regulation
in eukaryotes.
• mRNA processing includes three major steps.
8.6 Gene Expression and Regulation
• mRNA processing includes three major steps.
– Introns are removed and exons are spliced together.
– A cap is added.
– A tail is added.
8.6 Gene Expression and Regulation
• Power Notes
mRNA processing: hi mendez occurs after transcription
but before mRNA leaves the nucleus. Introns are removed
and the exons are spliced together. Introns are intervening
sequences of DNA.
- Exons are sequences of DNA that are expressed in the
protein.
- A cap is added that helps mRNA bind to a ribosome and
prevents the strand from being broken down too quickly.
- A tail is added that helps mRNA exit the nucleus.