Download Regulation of Gene Expression

Regulation of Gene
Expression
Questions?
How can cells with different functions have
the exact same DNA in their nucleus?
How does the body use the exact same set of
instructions to make different structures?
Core Concepts
• DNA triplets code for how many amino acids? (Codons)
• Amino acids link together and form polypeptides
• Genes code for polypeptides that control things like?
• Gene expression can happen in 2 ways, positive and negative
• Very small percentage of human genome codes for protein
Prokaryotic VS Eukaryotic Gene Expression
Differences in the Regulation of Gene Expression of Prokaryotic and Eukaryotic Organisms
Prokaryotic organisms
Eukaryotic organisms
Lack nucleus
Contain nucleus
DNA is found in the cytoplasm
DNA is confined to the nuclear compartment
RNA transcription and protein formation
occur almost simultaneously
RNA transcription occurs prior to protein
formation, and it takes place in the nucleus.
Translation of RNA to protein occurs in the
cytoplasm.
Gene expression is regulated primarily at the
transcriptional level
Gene expression is regulated at many levels
(epigenetic, transcriptional, nuclear shuttling,
post-transcriptional, translational, and posttranslational)
Gene Expression in Prokaryotes
• Transcriptional Control: the cell can speed up or slow down the
transcription of mRNA from the gene that codes for the polypeptide
• Post-transcriptional Control: the cell may transcribe the mRNA but
break it down before translation. It can also modify the poly-A tail.
WHY?
• Post-translational Control: after synthesizing the polypeptide the cell
can modify it chemically or vary the rate at whish the polypeptide
becomes a functional protein
OPERONS
• Stretch of DNA that contains one or more genes involved in a metabolic pathway along
with a regulatory sequence called an operator
OPERATOR
• DNA sequence located between promoter sequences and gene sequences that govern
whether RNA polymerase can bind to the promoter sequence to begin transcription
REPRESSOR
• Protein that binds to the operator to make it impossible for the RNA polymerase to bind
to the promoter, thus preventing genes from being transcribed
INDUCER
• Substance such as lactose molecule that stops the action of the repressor, allowing RNA
polymerase to bind to the promoter sequence and begin transcription
lac Operon- E-coli Bacteria
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Negative Gene Regulation in the lac Operon
• Uses a REPRESSOR (protein) which binds to the operator region and
doesn’t allow for RNA polymerase to bind to the promoter, resulting
in the lac operon not being transcribed.
Positive Gene Regulation in the lac Operon
• Uses ACTIVATORS (molecule that promotes action of enzymes), specifically
Catabolic Activator Protein (CAP), that stimulates gene expression by
binding to a cAMP molecule and then to s site near the Plac promoter.
• This action allows RNA polymerase to bind to the promoter easily and
speeds up the rate at which lac genes are transcribed.
Negative Gene Expression:
-Like a key for a car, your turning it on or off
(turning off transcription/translation).
Positive Gene Expression:
-Like the gas pedal and brake, accelerating
and slowing it down (accelerating and
slowing down transcription/translation).
Gene Expression in Eukaryotes
https://www.youtube.com/watch?v=KKR28Y_L4CA
• Pre-transcriptional control: the cell controls the extent to which DNA is
exposed to transcription enzymes, regulating DNA’s availability for
transcription.
• Transcriptional control: the cell controls whether or not exposed DNA is
transcribed into Pre-mRNA.
• Post-transcriptional control: the cell controls the rate of processing of premRNA, but then controls.
• Translational control: the cell manufactures the mRNA, but then controls
its transport to ribosomes in the cytoplasm
• Post-translational control: the cell manufactures the polypeptide but then
modifies it chemically or varies the rate at which it becomes a functional
protein. It may also break down the polypeptide before it becomes
functional
Activity:
• Choose a positive or negative example of gene
expression in Eukaryotes, then draw and label it.