Transcript Gene Regulation - yayscienceclass

Four of the many
different types of
human cells:
They all share the
same genome.
What makes them
different?
 Genes
are expressed as traits
 Traits are proteins or result
from reactions which are
regulated by proteins, such as
enzymes.
 Genes are expressed through
protein synthesis.
How Does A Cell Know?
Which Gene To Express
&
Which Gene Should Stay
Silent?
◦ In cellular differentiation:
 Certain genes are turned on and off.
 Cells become specialized in structure and function.
◦ In gene expression:
 A gene is turned on and transcribed into RNA.
 Information flows from genes to proteins, genotype to
phenotype.
◦ The regulation of gene expression plays a central role in
development from a zygote to a multi-cellular organism.
 When
a Gene is
Expressed:
◦ It is active and is
Transcribed into mRNA
 When
a Gene is Silent:
◦ It is in active and is Not
Transcribed
RNA polymerase: RNA polymerase
(RNAP or RNApol) is an enzyme that
produces RNA.
 Repressor: inhibits transcription of
structural genes by binding to the
operator
 Regulatory gene: codes for the
repressor
 Promoter: area on the DNA to which
the RNA polymerase attaches to begin
transcription

 Operator:
area of the DNA to
which the repressor binds;
“on/off” switch
 Structural genes: code for
enzymes which leads to a product
 Expression
Regulated By
1. Promoters
 RNA Polymerase Binding Sites
 Certain DNA Base Pair Sequences
2. Start & Stop Base Pair Sequences
3. Regulatory Sites
 DNA Binding Proteins
 Regulate Transcription
 What
is an Operon?
 Group of Genes That Operate Together
 For
Example:
◦ E. coli ferments (digests) lactose
 To Do That It Needs Three Enzymes
(Proteins), It Makes Them All At Once!
 3 Genes Turned On & Off Together. This is
known as the
lac Operon (lactose Operon)
 Operon:
made of three parts
1. Operator
2. Promoter
3. Group of genes

located together which
express proteins for a
similar function.
1.
Inducible
◦ Example: lac operon
 Lac = lactose
◦ Normally off but can be activated
2.
Repressible
◦ Example: trp operon
 Trp = tryptophan
◦ Normally on but can be inhibited
The lac Operon
◦
◦
Regulates Lactose Metabolism
It Turns On Only When Lactose Is Present &
Glucose is Absent.
Lactose is a Disaccharide
◦
A Combination of Galactose & Glucose
To Ferment Lactose E. coli Must:
1. Transport Lactose Across Cell Membrane
2. Separate The Two Sugars
Each Task Requires A Specific Protein
but
Proteins Not Needed If Glucose Present
(why waste energy if you already have food?)
so
Genes Coding For Proteins Expressed Only
When There Is No Glucose Present But
Lactose Is Present
ADD LACTOSE
= Lactose
Key Concept:
The lac Genes Are:
Turned Off By Repressors
And
Turned On By The Presence
Of Lactose

Operon Has 2
Regulatory Regions
1. Promoter (RNA
Polymerase Binding)
2. Operator (O
region) Bound To A
lac Repressor
 lac Repressor
◦ When Bound To O
Region : Prevents
Binding of RNA
Polymerase To
Promoter
◦ Turns The Operon
“OFF”

lac Repressor Also Binds
To Lactose
◦ Higher Affinity For Lactose

When Lactose Present
lac Repressor Is Released
From O Region
◦ Allows Transcription of All
Three Genes
1.
2.
3.
Based On Repressors
Based On Enhancers
Regulated At Protein Synthesis
Operons Usually
NOT Found In Eukaryotes
Key Concept:
Most Eukaryotic Genes Are Controlled
Individually And Have Regulatory
Sequences That Are Much More
Complex Than Prokaryotic Gene
Regulation
 TATA
Box
◦ About 30 Base Pairs Long
◦ Found Before Most Genes
◦ Positions RNA Polymerase
◦ Usually TATATA or TATAAA
◦ Promoters Usually Occur Just Before
The TATA Box
Enhancer Sequences
◦ Series of Short DNA Sequences
◦ Many Types
Enormous Number Of Proteins Can Bind To
Enhancer Sequences
◦ Makes Eukaryote Enhancement Very Complex

Some Enhance Transcription By Opening Up
Packed Chromatin

Others Attract RNA Polymerase

Some Block Access To Genes

Key To Cell Specialization
◦ All Cells Have Same Chromosomes
◦ Some Liver, Skin, Muscle, etc.