Section 14.3 Gene Expression and Regulation Part 1 This PowerPoint provides an overview of Prokaryotic and Eukaryotic Gene Regulation. Students- do not only use this PowerPoint to study, you also have your notes to help you prepare.

Write down the function / definition of each of the following words: Lac operon Promoter Operator Repressor RNA polymerase Lactose Transcription Draw the picture in the top left corner of page 452. Make sure your picture is labeled.

Write down the function / definition of each of the following words: Draw the TOP picture on page 453. Make sure your picture is labeled. Gene expression TATA box RNA polymerase Transcription factors Enhancers Cell specialization

Prokaryotic Gene Regulation To conserve energy and resources, cells control which genes they express. 4288 genes code for proteins in E. coli Example- cluster of 3 genes that must be turned on together before E. coli can break apart lactose (provides food for the bacterium) 3 lactose genes in E. coli = the lac operon Operon = a group of genes that are regulated together

Prokaryotic Gene Regulation: Lac Operon Lactose = galactose and glucose Proteins coded for by the genes of the lac operon break down lactose Environment with lactose = lac operon genes are transcribed Environment without lactose = lac operon genes are NOT transcribed

Prokaryotic Gene Regulation: Promoters and Operators Two regulatory regions: Promoter (P) Site where RNA polymerase binds to start transcription Operator (O) Site where a DNA-binding protein called the lac repressor can bind to DNA

Prokaryotic Gene Regulation: The Lac Repressor Blocks Transcription When lactose is NOT present in the environment: Lactose repressor binds to the operator (O) region RNA polymerase cannot reach the genes to start transcription The operon is “off” E. coli does not need to transcribe the lac operon because lactose is not in the environment (so the cell does not need to make proteins to break it down)

Prokaryotic Gene Regulation: Lactose Turns the Operon “On” When lactose IS present in the environment: Lac repressor has a binding site for lactose Lactose from environment enters cell and binds to lac repressor Changes shape of repressor Repressor falls off operator RNA polymerase is now able to bind to promoter to start transcription The operon is “on” E. coli will transcribe the lac operon because lactose is in the environment (so the cell will make proteins to break down lactose)

Eukaryotic Gene Expression More complex Example- TATA box Short regions of DNA (25-30 base pairs) before the start of a gene Binds a protein that helps position RNA polymerase by marking a point just before the beginning of a gene

Eukaryotic Gene Regulation: Transcription Factors DNA-binding proteins Control the expression of genes by binding DNA sequences in the regulatory regions Examples: Open up tightly packed chromatin to attract RNA polymerase to start transcription Block access to certain genes (similar to prokaryotic repressors)

Eukaryotic Gene Regulation: Transcription Factors Can activate many genes at once  dramatically affecting patterns of gene expression Example- Steroid hormones Steroid hormones are chemical messengers that enter cells and bind to receptor proteins These hormone-receptor complexes act as transcription factors that bind to DNA and activate multiple genes

Eukaryotic Gene Regulation: Cell Specialization Most cells in a multicellular organism have the same DNA Complex gene regulation: Allows cells to be differentiated / specialized Allows a zygote to develop into a functioning multicellular organism

Happy Wednesday  You need: Reminders: Hox gene half-sheet Notes Pen or pencil Reminders: Quiz Friday- 2nd half of Section 14.3 AND all of Section 14.4 Notes due Tuesday- Section 12.4 in yellow book

Section 14.3 Gene Expression and Regulation Part 2 Students- do not only use this PowerPoint to study, you also have your notes to help you prepare.

Genetic Control of Development Regulating gene expression is especially important during the earliest stages of development. The activation of genes in different parts of an embryo causes cells to differentiate.

Homeotic Genes Example- a specific group of genes controls the identities of body parts in the embryo of the common fruit fly Change one of these genes, and a part intended to be one body part could develop into a another body part. Homeotic genes (master control genes)- regulate organ development Master control genes are like switches that trigger particular patterns of development and differentiation in cells and tissues.

Homeotic Genes Homeotic genes share a very similar 180-base DNA sequence, called the homeobox. Homeobox genes- code for transcription factors that activate other genes important in cell development and differentiation. Hox genes- Arranged from top to bottom (head to tail) In fruit flies- determine each body segment In humans- tell the cells of the body how to differentiate as the body grows

Homeotic, Homeobox, and Hox Genes Homeotic genes regulate organ development. Homeobox genes code for transcription factors. Hox genes determine the identities of each body segment. Tell students: The work of American biologist Edward B. Lewis made it clear that a set of master control genes, known as homeotic genes, regulate body parts that develop in specific parts of the body. Click to display the summary point. Explain that the molecular studies of homeotic genes show that they all share a very similar 180-base DNA sequence, which was given the name homeobox. Homeobox genes code for transcription factors that activate other genes that are important in cell development and differentiation. Point out that, in flies, a group of homeobox genes known as Hox genes are located side by side in a single cluster. Hox genes determine the identities of each segment of a fly’s body. Ask: What section of the bodies of flies and mice is coded by the genes shown in blue? Answer: the back of the body; posterior portion of the abdomen of the fruit fly and rump of the mouse

Epigenetics When chromatin is tightly packed…gene expression is blocked. When chromatin is opened up…gene expression is enhanced. Cells regulate chromatin by enzymes that attach chemical groups to DNA and histones: Methyl groups (--CH3) will cause chromatin to condense, blocking transcription. Acetyl groups (--CO-CH3) will open chromatin up for transcription and gene expression.

Epigenetics Epigenetics- above the level of the genome Epigenetic marks do not change DNA base sequences. They influence patterns of gene expression over long periods of time.

Environmental Factors Temperature Salinity Nutrient availability Insufficient nourishment during the first three months of pregnancy