12-5 Gene Regulation
12-5 Gene Regulation
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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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Gene Regulation: An Example
How are lac genes turned off and on?
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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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Gene Regulation: An Example
On one side of the operon's three genes are two regulatory regions.
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Gene Regulation: An Example
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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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Gene Regulation: An Example
When lactose is added, sugar binds to the repressor proteins.
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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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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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Eukaryotic Gene Regulation
How are most eukaryotic genes controlled?
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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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Eukaryotic Gene Regulation
Many eukaryotic genes have a sequence called the TATA box.
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Promoter
sequences
Upstream
enhancer
TATA
box
Introns
Exons
Direction of transcription
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Eukaryotic Gene Regulation
The TATA box seems to help position RNA polymerase.
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Promoter
sequences
Upstream
enhancer
TATA
box
Introns
Exons
Direction of transcription
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Eukaryotic Gene Regulation
Eukaryotic promoters are usually found just before the TATA box, and consist of short DNA sequences.
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Promoter
sequences
Upstream
enhancer
TATA
box
Introns
Exons
Direction of transcription
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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:
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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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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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Development and Differentiation
Hox Genes
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Fruit fly chromosome
Fruit fly embryo
Adult fruit fly
Mouse chromosomes
Mouse embryo
Adult mouse
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