Gene Regulation

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Gene Regulation

Regulation through Operons

Transcription Factors (instead of operons)

repressors

activators

operons do not occur in eukaryotic cells - made in mRNA w/ individual promoter

enhancers

bind activator proteins

activator bound to receptor is brought to promoter via DNA bending proteins

transcription increased via RNA polymerase II

basal (general) expression

specific to eukaryotes (ex. humans)

Activators/Repressors involvement in regulation of gene expression

Operons

Helps with regulation with an on-off switch

"Switch"

Negative regulation

Postive regulation

Segment of DNA known as an "operator"

Positioned within promoter

Proteins bind to operators to turn on gene expression for multiple genes

OR to turn off expression

Eukaryotes

Transcription factors

Control elements in DNA

Distal

Bind to specific transcription factors

Can be close or far from gene they are controlling

Sequences in DNA upstream or downstream of gene

Enhancers

Proximal

Bind general transcription factors

Sequences in DNA close to promoter

Specific

Bind to distal control elements called enhancers

Present near or far from gene they are controlling

Change levels of transcription

High levels of transcription are reduced by repressors

Increase levels of transcription

Done by activators

General

Bind to promoter and regions near

Low levels of transcriptions

Background/basal

Proteins that help turn specific genes "on" or "off"

Help increase or decrease level of transcription

Prokaryotes

Regulation Through Operons

Lac Operon

Lactose present, glucose present (cAMP level low)

Presence of Glucose operon OFF

Blocks Adenylyl Cyclase

Prevents production of cAMP

CAP cannot be activated

CAP can't help RNAP to bind promoter

Little lac mRNA synthesized

Lactose present, repressor inactive, operon on

mRNA translates= B-Galactosidase, Permease, Transacetylase

Takes in more Lactose from outside

Break it down to glucose and galactose

Uses sugars as needed

All structural genes are transcribed

Forms a long mRNA

No glucose= operon ON

Inducible operon

Lactose present, glucose scarce (cAMP level high)

Activator protein CAP is activated by cAMP

CAP helps RNAP to bind promoter

Facilitates transcription

Operon ON: Induced/ high expression

Abundant lac mRNA synthesized

Lactose absent, repressor active, operon off

Negative regulation of operon

Transcription of structural genes is blocked

Lac= Lactose

Inducer of the lac operon

Disaccharide made of glucose and galactose

Example of negative and positive regulation

Regulation needs both repressor and operator

Negative regulation= gene expression OFF

Without repressor, transcription occurs

With repressor, no transcription occurs

Repressor protein bond to operator sequence

Positive regulation= gene expression ON

Without activator, no transcription occurs

With activator, transcription occurs

expression at high level

Occurs at level of transcription

Gene Organization

Regulatory regions

Operator

Turn off gene expression

Turn on gene expression

Location where protein binds

The binding causes positive/negative regulation

Proteins are called activators/repressors

“Switch” is a segment of DNA

Promoter

Occurs structural and regulatory gene/s

Regulatory gene

Lac I

Codes for repressor protein

Structural genes

Genes whose expression is controlled together

Lac Z

Structural Gene for B-Galactosidase

Lac Y

Structural Gene for B-Galactoside permease

Lac A

Structural Gene for B-Galactoside transacetylase

Activators/Repressors are Activated/Made

Far Away from the Gene

Activators bind to mediator proteins

Brings the activator closer to the promotion site

DNA bending brings activator closer to promotion site

Activator binds to enhancer

Specific Transcription Factor

Turns gene regulation on or off

Last gene that enters the nucleus

Negative Regulation

Operon Gene Regulation Off

Repressor

Positive Regulation

Operon Gene Regulation On

Activator

Binds to operator

Protein