Download 8.6 Gene Expression and Regulation

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
• 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
• When lactose is absent a rpressor protein binds to the operon
and blocks RNA polymerase from transcribing genes. (lac
operon “off”)
• When lactose is present it binds to the receptor protein which
blocks the repressor from binding to the operon. RNA
polymerase can then transcribe genes. (lac operon “on”)
8.6 Gene Expression and Regulation
Question:
• Why is the lac operon an advantage to a bacterial cell?
8.6 Gene Expression and Regulation
Answ
• Cell does not waste energy making enzymes to digest
lactose when lactose is not present
8.6 Gene Expression and Regulation
Bell ringer
• 1-If the codon is GGG what is the anticodon?
• 2-If the DNA template strand reads ATT what is the
codon? Anticodon?
• 3-How many times does replication occur?
• 4-How many times can transcription occur?
• 5-If the tRNA molecule has the anitcodon of AGU what
amino acid would it carry? (hint determine the codon)
• Have your SG 8.1-8.3 on the side of your desk!
8.6 Gene Expression and Regulation
Every cell in your body has the same set of DNA BUT
our cells are not the same!
• Cells differ from each other because different sets of
genes are expressed in different types of cells.
• Eukaryotic cells can control/ regulate gene expression at
several different points BUT one of the most highly
regulated steps is at the start of transcription.
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
– Most eukaryotes have a TATA box promoter.
(seven nucleotide promoter TATAAAA)
– 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.
– 1-Introns are removed and exons are spliced together.
– 2-A cap is added.
– 3-A tail is added.
8.6 Gene Expression and Regulation
Question
• Where does mRNA processing occur in the cell?
8.6 Gene Expression and Regulation
Question
• Which parts of a gene are expressed as a protein?
(introns or exons) How do you know?