Control of Gene Expression

Big Idea 3: Living systems store, retrieve, transmit, and respond to

info essential to life processes.

Essential Knowledge

• 3B1: Gene regulation results in differential gene expression, leading to cell specialization.

• 3B2: A variety of intercellular and intracellular signal transmissions mediate gene expression

Much Diversity due to Gene Expression

• Each tissue in our body is very different despite having the same DNA

• Even identical twins have many differences due to gene expression

Some Basics: Regulatory Sequences

• Stretches of DNA that interact w/ regulatory proteins to control transcription.

• Allows RNA Polymerase to bind on. – AKA promoter (TATA box)

– Enhancers are sequences that increase transcription

Some Basics: Regulatory Genes

• Code for proteins or mRNAs which affect gene expression– Ex: microRNAs–Repressor proteins– Transcription factors/ enhancers

Some Basics: Operons

• Simple gene expression mechanisms in prokaryotes

Components of the Operon

• Operator, sequence next to the promoter (On/Off switch) If repressor protein is on it, then off…can’t

make genes• Promoter (where RNA polymerase binds)

• Genes that work together

Types of Operons• Some genes are normally

“off” and can be turned “on” Presence of a molecule induces gene expression or enhances gene expression

• Some genes are normally “on” and can be turned “off” Presence of a molecule represses gene expression

Inducing Gene Expression: Lac Operon, + Control

• If lactose present, bacteria need to make lactase to break it down.

• Lactose binds to repressor on operator repressor is released from operator

• RNA polymerase now fits onto promoter region to make mRNA protein lactase.

Negative ControlCase Study: Trp Operon

• Tryptophan fits in repressor blocks RNA polymerase.

• Once out of tryp, repressor changes shape to allow promoter available to make more tryptophan turns transcription on.

Ribosomal Genes…

• Always on!!! Always Expressed!

In Eukaryotes…

• No operons…• Gene expression involves regulatory genes,

regulatory elements, and transcription factors. All work together to determine how much

product is made.

Transcription Factors• Bind to specific DNA sequences

• Some activate (increase expression) and some are repressors (decrease expression)

Signal Transmission

• Within and b/t cells mediates gene expression.

• Ex: cytokines regulate gene expression to allow cell replication and division.

• Within and b/t cells mediates cell function.• Ex: HOX genes (homeotic genes)

Signal Transmission

Mr Anderson

• http://www.youtube.com/watch?v=3S3ZOmleAj0

Lac Operon or Trp Operon Flow Map