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7 Control Sites in the DNA -> RNA -> Protein Scheme

1. Chromosomal Placement - gene located in eu- or heterochromatin
2. Transcriptional - DOMINANT control mechanism
3. RNA Processing - which RNA's mature
4. RNA Transport/Localization - which mRNA's leave nucleus and to where
5. Translational - fine tuning at ribosome
6. Turnover of mRNA - the half-life of certain mRNA's
7. Protein Activity - post-translational activity, folding, turnover, compartmentalization

Amount of a Particular Protein/mRNA =

= (Synthesis - Degradation)

Polycistronic

mRNA codes for more than one protein. Found mainly in Prokaryotes.

Promoter

Region to which RNA polymerase and other factors necessary for transcription bind.

Transcribed Region

contains protein coding information and untranslated 5' and 3' sequences

Prokaryotic Promoters

Core Promoter Elements: contact components of RNA polymerase.

Enhancer/Silencer Elements: bind specific transcriptional factors that alter the rate of transcriptional initiation or elongation.

Operon

Expression unit consisting of collection of genes (that produce proteins with complementary functions), the operator, and promoter (all the genes within the operator are regulated collectively).

3 Genes of the Lac Operon

1. galactoside permease (lacY) -- transporter
2. beta-galactosidase (lacZ) -- catabolic enzyme
3. galactoside transacetylase (lacA)

Galactoside Permease catalyzes:

movement of lactose into the bacterial cell

beta-Galactosidase catalyzes:

1. the breakdown of Lactose into Glucose + Galactose
2. the formation of Allolactose from Lactose (Impt for regulation)

Repressor Mechanism in the Lac Operon

...

CRP (cyclic AMP receptor protein)

Binds to the CRP site on the Lac Operon with cAMP as a cofactor and activates transcription when glucose is LOW. Low glucose = high cAMP.

Mechanism of CRP Activation of Lac Operon

...

Trp Operon

Contains 5 genes for the enzymes needed for E. coli to synthesize Tryptophan.

2 Mechanisms of Trp Operon Regulation

1. Repression by Trp Repressor -- binds to Operator in presence of Tryptophan
2. Transcriptional attenuation in presence of Tryptophan

Transcriptional Attenuation Mechanism (High Trp)

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Transcriptional Attenuation Mechanism (Low Trp)

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