Regulation of GeneExpression
Sec. 6.4 (p.267)
Control Mechanisms42,000 genes code for proteins in Humans
Are the proteins for all of these genes beingmade all the time??
No!
Why?? Gene Regulation• Proteins are needed at certain times (E.g. Hormones and proteins)• Do the islets of langerhans continually
produce insulin?
What would happen if genes were expressed all the time?
If genes were always expressed, theywould always make protein.
Example: Insulin• Insulin is only required in cells with high glucose
levels . • Insulin causes cells in the liver, muscle, and
fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle.
• If we produce too much insulin then too much glucose is taken out of the blood and you get low blood sugar.
Transcription Factors
Genes can be turned “on” or “off” by proteins thatswitch on genes by binding to DNA.• In turn, they help RNA polymerase to bind
RNA Polymerase can't find the promoter.
RNA Polym-erase
RNA Polym-erase
promotor
promotor
transcription factors act like flags for RNA Polymerase, helping it to find the promoter
Certain Transcription Factors bind to specific regions on the DNA.
What do you think are the functions of the following transcription Factor Types and DNA sequences?
Which ones do you think pair up and bind together?
Transcription Factor DNA SequenceActivator SilencerRepressor Enhancer Basal Level Transcription Factors TATA Box
Types of Transcription Factors
House Keeping Genes(AKA: Constitutive genes)
• Genes are turned ‘ON’ all the time –not regulated.
• Vital to an organism’s life• Examples??
Four Levels of Control
• The extent to which they are transcribed is regulated (transcriptional and
posttranscriptional)• The extent to which they are translated is
regulated (translational and postranslational)
Gene Regulation: OperonsGene regulation mechanisms in prokaryotes
Operon: A cluster of genes grouped togetherunder the control of one promotor.
• Each operon contains a promoter, operator and genes
General Structure Definitions
The operon consists of:Promoter• a section of DNA where RNA polymerase bindsOperator• a section of DNA that interacts with the repressor
protein to alter transcriptionRegulatory genes• code for the repressor proteinStructural genes• code for the target proteins
Lactose
• Type of Macromolecule?• Lactose makes up around 2-8% of the solids in
milk
• Consists of Glucose and Galactose
Lactose Intolerance
Undigested lactose remains in the gut and bacteria feed on it, causing the typical symptoms:
- stomach cramps- nausea- bloating- acid reflux- flatulence
Can't digest lactose because don't have enough lactase
lac Operon
Produces B-galactosidase- enzyme that breaks down lactose- remember: lactase breaks down lactose andB- galactosidase degrades it- produced after lactose has been ingested(therefore when lactose levels are high)
Inducible operon: lactose present induces transcription
trp Operon
Produces tryptophan- A non-essential amino acid- Produced when none has been ingested(when tryptophan levels are low)
Trp operon is normally active, unless a repressor turns it off.
• How is regulation in Eukaryotes different?• See pg 269-270
• Read section 6.4 & try question25,27,28,29 pg 269,
• Pg 272 questions;
Gene Regulation in Eukaryotes5 levels of control
pre-transcriptional
transcriptionalpost-transcriptionaltranslationalpost-translational
Histones and nucleosomeskeep DNA tightly wrapped
transcription factors mRNA modification RNA interference Protein modification of
shape or ubiquitin tag
Eukaryotic gene control
• Genes are not organized into operons• They require a much more elaborate control• Ie. many activators, and enhancer regions on
DNA to regulate gene control under certain conditions. Pg 270
• Homework
• More review if needed• Page 267-272 #2-8
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