Gene Regulation

Protein

Binds to operator

Positive Regulation

Activator

Operon Gene Regulation On

Negative Regulation

Repressor

Operon Gene Regulation Off

Specific Transcription Factor

Last gene that enters the nucleus

Turns gene regulation on or off

Far Away from the Gene

Activator binds to enhancer

DNA bending brings activator
closer to promotion site

Activators bind to mediator proteins

Brings the activator closer to
the promotion site

Gene Organization

Structural genes

Genes whose expression is controlled together

Lac A

Structural Gene for B-Galactoside transacetylase

Lac Y

Structural Gene for B-Galactoside permease

Lac Z

Structural Gene for B-Galactosidase

Regulatory gene

Lac I

Codes for repressor protein

Regulatory regions

Promoter

Occurs structural and regulatory gene/s

Operator

“Switch” is a segment of DNA

Location where protein binds

Proteins are called activators/repressors

The binding causes positive/negative regulation

Turn on gene expression

Turn off gene expression

Regulation Through Operons

Occurs at level of transcription

Positive regulation= gene expression ON

expression at high level

With activator, transcription occurs

Without activator, no transcription occurs

Negative regulation= gene expression OFF

Repressor protein bond to operator sequence

With repressor, no transcription occurs

Without repressor, transcription occurs

Lac Operon

Example of negative and positive regulation

Regulation needs both repressor and operator

Lac= Lactose

Disaccharide made of glucose and galactose

Inducer of the lac operon

Lactose absent, repressor active, operon off

Transcription of structural genes is blocked

Negative regulation of operon

Lactose present, glucose scarce (cAMP level high)

Abundant lac mRNA synthesized

Operon ON: Induced/ high expression

Activator protein CAP is activated by cAMP

CAP helps RNAP to bind promoter

Facilitates transcription

Lactose present, repressor inactive, operon on

No glucose= operon ON

Inducible operon

All structural genes are transcribed

Forms a long mRNA

mRNA translates= B-Galactosidase, Permease, Transacetylase

Takes in more Lactose from outside

Break it down to glucose and galactose

Uses sugars as needed

Lactose present, glucose present (cAMP level low)

Little lac mRNA synthesized

Presence of Glucose operon OFF

Blocks Adenylyl Cyclase

Prevents production of cAMP

CAP cannot be activated

CAP can't help RNAP to bind promoter

Transcription factors

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

Help increase or decrease level of transcription

General

Low levels of transcriptions

Background/basal

Bind to promoter and regions near

Specific

Change levels of transcription

Increase levels of transcription

Done by activators

High levels of transcription are reduced by repressors

Bind to distal control elements called enhancers

Present near or far from gene they are controlling

Control elements in DNA

Proximal

Sequences in DNA close to promoter

Bind general transcription factors

Distal

Enhancers

Sequences in DNA upstream or downstream of gene

Can be close or far from gene they are controlling

Bind to specific transcription factors

Operons

Helps with regulation with an on-off switch

"Switch"

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

Postive regulation

Negative regulation

Gene Organization

Proximal

basal (general) expression

specific to eukaryotes
(ex. humans)

Distal

enhancers

bind activator proteins

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

transcription increased via
RNA polymerase II

Regulation through Operons

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

Transcription Factors
(instead of operons)

activators

repressors