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Consider the following…

Delve into the intricate world of gene expression, DNA packing, X chromosome inactivation, alternative RNA splicing, homeotic genes, epigenetics, and DNA microarrays. Explore how cells differentiate to perform unique functions in your body.

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Consider the following…

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  1. 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?

  2. Gene Expression & The Lac Operon

  3. Other Kinds of Operons

  4. 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.

  5. 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

  6. 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

  7. 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

  8. X Inactivation & Cat Fur - Tortoiseshell

  9. X Inactivation & Cat Fur - Calico

  10. 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

  11. 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

  12. 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

  13. The Agouti Mice

  14. 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?

  15. 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

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