Gene Expression Objectives: 1.Explain how genes expression is controlled in prokaryotes. 2. Explain how gene expression is controlled in eukaryotes.  Lac Operon  Promoter  Operator  Repressor  Transcription factors  Gene expression  Cellular differentiation  Stem cell  Pluripotent; Multipotent  Epigenetics  Methylation  Histone Modification Vocabulary

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  All somatic cells contain a complete set of chromosomes  Not all genes get transcribed and translated. Example:  Skin cells will not translate genes to make hemoglobin, or insulin.

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.

Stem cells Pluripotent (can become any type of cells) or multipotent (many types of cells) Stem cell research Potential to help cure/treat conditions involving damaged cells (replace cells of damaged spinal cords, or cardiac muscles, etc.) Tutorial on stem cells:

Stem cells & Therapeutic Cloning  Use embryonic stem cells to create specialized human cells.  Goal: Cure disease  Embryo does not develop into a human. Allowed in U.S. (state by state) w/ restrictions

Why do people bank cord blood? h.com/top-10-cord- blood-banks/ Sources of Stem Cells 1.Embryonic cells (after fertilization to a few weeks) 2.Placenta & Umbilical cord blood 3.Bone marrow in adults

What Controls Which Genes Get Translated (Expressed)? Prokaryotes (bacteria) Eukaryotes Operon System  Promoter and Operator sequence before genes  Switch on/off genes Transcription factors

Prokaryotes: Gene Expression Operon = Promoter + Operator + Genes Promoter = where RNA polymerase binds. Operator = Where repressor protein binds. Operon Off Repressor protein binds to operator when lactase is not needed. Stops transcription of genes. Operon On Lactose present  binds to repressor protein. Repressor released, genes transcribed.

Gene Expression in Prokaryotes & The Lac Operon Animation

Prokaryotes: lac operon system Operon: sequence of instructions for turning on/off transcription. Located before gene sequences. Includes “promoter” and “operator” sequences. Promoter: RNA polymerase binds to; “starting line” for transcription. Operator: site where Repressor protein binds and STOPS TRANSCRIPTION (when proteins are not needed)

lac operon system Repressor protein: binds to operator site  prevents transcription Repressor proteins alternate shape! Lactose present: binds to repressor protein & changes repressor shape; repressor DOES NOT fit on operator site; genes transcribed; proteins for lactose digestion made. Lactose not present; repressor shape allows it to bind to operator and STOP transcription (proteins not needed).

Animation of lac operon system McGraw Hill animation of lac operon Eukaryotic Gene Expression: Transcription Factors More complex than prokaryotes

 More elaborate (than prokaryotes)  Genes are not controlled in clusters Eukaryotes: Gene Expression Proteins called transcription factors regulate transcription by binding to promoters or RNA polymerase  Turned ON or OFF by chemical signals in the cell

Eukaryotes: Gene Expression

Epigentics: Gene Expression Epigenetics Environmental factors (chemicals or temperatures) can activate or deactivate genes and influence the expression of those genes in future generations /epigenetics-how-our- experiences-affect-our-offspring

The Agouti Mice

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 NOVA clip (14min)

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 (protein contact with DNA) Some regions of interphase chromosomes (chromatin) are highly packed like mitotic chromosomes The genes in these packed regions are generally not expressed

How are genes turned on or off? 1. Methylation: Methyl groups added to DNA turn off transcription. 2. Histone modification: Proteins bind to histones (proteins that DNA is wrapped around) and causes histones to tighten DNA coiling  turn off transcription What causes methylation or histone modification????

Gene Expression: 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

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

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 NOVA introduction 13 minutes Agouti mice video Gene switches (PBS) slide show Ghost in Your Genes (PBS) Epigenome at a Glance Articles for Epigentics mark-on-your-genes offspring#