Transcript Control of Gene Expression - Downtown Magnets High School

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 Control
Case 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.
Signal Transmission
• Within and b/t cells mediates cell function.
• Ex: HOX genes (homeotic genes)
Mr Anderson
• http://www.youtube.com/watch?v=3S3ZOmle
Aj0
Lac Operon or Trp Operon Flow Map