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Negative Feedback
Keeps things the same in cells
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Tryptophan and Enzyme 2 and 3
When Tryptophan is present, it makes Enzymes 2 and 3 are almost useless because they won't be made
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Operator
- segment of DNA positioned within the promoter that acts as regulatory "switch"
- part of the operon
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Operon
- entire stretch of DNA that includes the operator, promoter, and genes they control
- can be switched off when protein repressor is present (repress means off)
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Two Types of Negative Gene Regulation
- Repressible operons
- Inducible operons
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Repressible operon
- binding of repressor to operator shuts off transcription
- usually on, making the repressor usually inactive
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Inducible operon
- inducer inactivates repressor and turns on transcription
- usually off, making the repressor usually active
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trp operon
When the repressor is inactive, transcription occurs
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Presence of lactose
Transcription occurs
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Lac Operon
- inducible
- normally off because the repressor is normally active
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Beta-Galactosidase
only produced when there is lactose
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Gene expresssion in eukaryotic cells
Can be regulated at any stage
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Chromatin
long, stringy form of DNA
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Histone acetylation and DNA methylation
regulate transcription by regulating the chromatin
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Histone acetylation
- acetyl groups are attached to lysines in histone tails
- loosens chromatin structure; promotes initiation of transcription
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DNA methylation
- addition of methyl groups to certain bases in DNA
- reduces transcription
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Post-transcriptional regulation
- has to do with mRNA splicing
- 1) mRNA degradation
- 2) initiation of translation
- 3) protein processing and degradation
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RNA interference (RNAi)
inhibition of gene expression by RNA molecules
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Gene expression during embryonic debelopment
The transformation from zygote to adult results from cell division, cell differentiation, and morphogenesis.
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Cytoplasmic determinants
- maternal substances in the egg that influence early development
- first place where differentiation occurs
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Pattern formation
- development of a spatial organization of tissues and organs
- begins with establishment of the major axes (animals)
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Positional formation
tells a cell its location relative to the body axes and to neighboring cells
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