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 enhancesgene 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.
Signal Transmission • Within and b/t cells mediates cell function. • Ex: HOX genes (homeotic genes)
Mr Anderson • http://www.youtube.com/watch?v=3S3ZOmleAj0