Transcript Consider the following*

Consider the following…
• Do all of the cells in your body carry out the
same processes?
• Do all of the cells in your body make the same
proteins?
• Do all of the cells in your body contain the
same genes?
• What is the connection between genes and
protein production?
• How is it possible for different types of cells to
exist in your body?
Gene Expression & The Lac Operon
Other Kinds of Operons
Cell Differentiation
•Differentiation is when cells become specialized in
structure and function
•It results from selective gene expression, the turning
on and off of specific genes.
Turning Eukaryotic Genes On & Off
•Eukaryotic RNA
polymerase needs assistant
transcription factor
proteins
•Activator proteins bind to
enhancers (not adjacent to
the gene)
•DNA bends & interacts
with other transcription
factors, facilitating correct
RNA polymerase
Gene Switches
attachment
DNA Packing Helps Regulate
Eukaryotic Gene Expression
•A single chromosome contains app.
4cm of DNA
•Coiling and folding enables all this
DNA to fit in the nucleus
•This packing prevents gene expression
by blocking transcription
proteincontact with DNA
•Some regions of interphase
chromosomes (chromatin) are highly
packed like mitotic chromosomes
•The genes in these packed regions are
generally not expressed
X chromosome Inactivation
• Female mammals
inherit 2 X
chromosomes, but do
not make twice as
much X-coded proteins
• One X in each somatic
cell condenses into a
compacted, inactive
Barr body.
• The same X is not
turned off in every cell
X Inactivation & Cat Fur - Tortoiseshell
X Inactivation & Cat Fur - Calico
Alternative RNA Splicing
• More than one type of polypeptide can result from a
single gene
• Different exons are spliced together as a result of
alternative splicing
Homeotic Genes
• Master control genes that
regulate the genes that
actually control the
anatomy of body parts
• Discovered by studying
bizarre fruit fly mutations
• Mutation in a single gene
led to legs growing out of
head in place of antennae
Epigenetics
• Heritable traits that do not involve changes in
the underlying DNA sequence (“in addition to
changes to the genetic sequence”)
• Used to describe any aspect other than DNA
sequence that influences the development of
an organism.
• Involves chemical modifications that “mark”
certain genes with a distinct signature;
“biological punctuation”
ex) Doctors v. Doctor’s
The Agouti Mice
When Epigentics Meets Pediatrics
• What is meant by the terms “epigenetics” and the
“epigenome”?
• Identify chemical groups known to modify genes
and influence gene expression.
• What is meant by the phrase “epigenetic
signatures”?
• How are epigenetic effects different from genetic
effects?
• What contributes to our epigenetic make-up or
profile?
DNA Microarray
(“DNA chip” /”Gene Chip”)
• Isolate mRNA transcribed
from genes in selected cell
• Mixed with reverse
transcriptase to form cDNA
(complementary) fragments
with fluorescent nucleotides
• Add cDNA to fixed DNA
fragments in microarray tray
• cDNA binds to
complementary bases
producing a detectable glow
• Non-binding DNA rinsed away