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Apr 01, 2015
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Biology
Biology
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12-5 Gene Regulation
12-5 Gene Regulation
Fruit fly chromosome
Fruit fly embryo
Adult fruit fly
Mouse chromosomes
Mouse embryo
Adult mouse
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12-5 Gene Regulation
Slide 3 of 26
Gene Regulation: An Example
Gene Regulation: An Example
E. coli provides an example of how gene expression can be regulated.
An operon is a group of genes that operate together.
In E. coli, these genes must be turned on so the bacterium can use lactose as food.
Therefore, they are called the lac operon.
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12-5 Gene Regulation
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Gene Regulation: An Example
How are lac genes turned off and on?
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12-5 Gene Regulation
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Gene Regulation: An Example
The lac genes are turned off by repressors and turned on by the presence of lactose.
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12-5 Gene Regulation
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Gene Regulation: An Example
On one side of the operon's three genes are two regulatory regions.
• In the promoter (P) region, RNA polymerase binds and then begins transcription.
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12-5 Gene Regulation
Slide 7 of 26
Gene Regulation: An Example
• The other region is the operator (O).
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12-5 Gene Regulation
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Gene Regulation: An Example
When the lac repressor binds to the O region, transcription is not possible.
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12-5 Gene Regulation
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Gene Regulation: An Example
When lactose is added, sugar binds to the repressor proteins.
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12-5 Gene Regulation
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Gene Regulation: An Example
The repressor protein changes shape and falls off the operator and transcription is made possible.
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12-5 Gene Regulation
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Gene Regulation: An Example
Many genes are regulated by repressor proteins.
Some genes use proteins that speed transcription.
Sometimes regulation occurs at the level of protein synthesis.
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12-5 Gene Regulation
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Eukaryotic Gene Regulation
How are most eukaryotic genes controlled?
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12-5 Gene Regulation
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Eukaryotic Gene Regulation
Eukaryotic Gene Regulation
Operons are generally not found in eukaryotes.
Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon.
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12-5 Gene Regulation
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Eukaryotic Gene Regulation
Many eukaryotic genes have a sequence called the TATA box.
Promotersequences
Upstreamenhancer
TATAbox Introns
Exons
Direction of transcription
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12-5 Gene Regulation
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Eukaryotic Gene Regulation
The TATA box seems to help position RNA polymerase.
Promotersequences
Upstreamenhancer
TATAbox
Introns
Exons
Direction of transcription
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12-5 Gene Regulation
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Eukaryotic Gene Regulation
Eukaryotic promoters are usually found just before the TATA box, and consist of short DNA sequences.
Promotersequences
Upstreamenhancer
TATAbox
Introns
Exons
Direction of transcription
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12-5 Gene Regulation
Slide 17 of 26
Eukaryotic Gene Regulation
Genes are regulated in a variety of ways by enhancer sequences.
Many proteins can bind to different enhancer sequences.
Some DNA-binding proteins enhance transcription by:
• opening up tightly packed chromatin
• helping to attract RNA polymerase
• blocking access to genes
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12-5 Gene Regulation
Slide 18 of 26
Development and Differentiation
Development and Differentiation
As cells grow and divide, they undergo differentiation, meaning they become specialized in structure and function.
Hox genes control the differentiation of cells and tissues in the embryo.
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12-5 Gene Regulation
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Development and Differentiation
Careful control of expression in hox genes is essential for normal development.
All hox genes are descended from the genes of common ancestors.
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12-5 Gene Regulation
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Development and Differentiation
Hox Genes
Fruit fly chromosome
Fruit fly embryo
Adult fruit fly
Mouse chromosomes
Mouse embryo
Adult mouse
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12–5
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12–5
Which sequence shows the typical organization of a single gene site on a DNA strand?
a. start codon, regulatory site, promoter, stop codon
b. regulatory site, promoter, start codon, stop codon
c. start codon, promoter, regulatory site, stop codon
d. promoter, regulatory site, start codon, stop codon
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12–5
A group of genes that operates together is a(an)
a. promoter.
b. operon.
c. operator.
d. intron.
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12–5
Repressors function to
a. turn genes off.
b. produce lactose.
c. turn genes on.
d. slow cell division.
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12–5
Which of the following is unique to the regulation of eukaryotic genes?
a. promoter sequences
b. TATA box
c. different start codons
d. regulatory proteins
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12–5
Organs and tissues that develop in various parts of embryos are controlled by
a. regulation sites.
b. RNA polymerase.
c. hox genes.
d. DNA polymerase.
END OF SECTION