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 attachment Gene Switches

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