Gene Regulation

Regulation in Prokaryotes Gene Expression = gene to protein processing that functions within cells. Regulation = We are talking about controlling gene transcription and translation. Produce proteins where and when they are needed !!

The Operon (Prokaryotes Only*) Operon - group of genes that operate together. Components: –Regulator gene –Promoter region –Operator gene –Structural genes

Promoter and Operator The promoter is where RNA polymerase binds to begin transcription. The operator is where repressor proteins bind to stop transcription When the repressor proteins are bound to the operator, RNA polymerase is unable to bind to the promoter. -Repressor Proteins bound to operator = RNA polymerase cannot bind = gene is “off” = no transcription -Repressor proteins not bound to the operator = RNA polymerase can bind = gene is “on” = transcription

All genes must be transcribed and translated RNA polymerase will move from left to right Promoter region is not itself a gene; rather is the place where polymerase will attach... Components of an Operon RG P Op SG1SG2SG3 Regulator Gene Promoter Region Operator Gene Structural Genes 1,2&3

Example of Regulation in Prokaryotes Earliest research was done in E. coli E. coli is single celled bacterium; changes functioning in relation to environmental cues.

The lac operon E. coli can use lactose as a food source by breaking down lactose into simple sugars. Specific proteins are needed to break down lactose into these sugars. E. coli only produces these proteins in the presence of lactose. How does the E. coli cell control when to produce these lactose proteins?

Regulation of the lac operon Figure –No lactose = the lac repressor protein is continuously bound to the operator = RNA polymerase cannot bind = no transcription –In the presence of lactose: The lac repressor protein has a binding site for lactose When lactose is taken in by the cell, it binds to the lac repressor protein and removes it from the operator. No repressor protein = RNA polymerase can bind to the promoter = gene is turned “on” = transcription

Other Forms of Regulation Repressor proteins are not the only way to regulate genes in prokaryotes Regulation can occur in: –The rate of transcription –Protein synthesis

Eukaryotic Gene Regulation Operons are generally not found in eukaryotes. Eukaryotic organisms have more complex ways of regulating their genes. Why is gene regulation more complex in eukaryotes?

Gene Regulation in Eukaryotes Every cell in our bodies contains all of our DNA (genome). If every cell contains every piece of DNA, why do we have different types of cells? –Different genes for each type of cell are transcribed, producing different types of proteins. What ways can cells regulate gene expression in eukaryotes?

TATA Box TATA Box – sequence of nucleotides that are found between the promoter and the start of transcription. –Marks a point just before transcription to help position RNA polymerase.

Enhancer Sequences -Enhancer Sequences- sequences of DNA located before the start of transcription -Many different types of proteins can bind to different enhancer sequences to affect transcription: -Opening up tightly-packed chromatin -Attract RNA polymerase

Gene Regulation and Development How does a fertilized egg become a multi- cellular adult? During embryonic development, cells differentiate into different types (muscle cells, nerve cells, etc). What causes this differentiation of cells during development?

Hox genes Series of genes that control differentiation of cells and tissues in an embryo. What would happen if a mutation were to occur in one of these genes? –A mutation in the hox genes could completely change the cell types that normally develop. Example: Drosophila- antennae can be replaced by legs

Answer Questions p. 326 #1-5 Due Monday, 2/28/11

Evolution Connection Pax 6: gene that controls eye growth in fruit flies –Similar genes that control eye growth exist in mammals such as mice. –When a copy of the mice gene was inserted into the “knee” DNA of a fruit fly embryo, the fly grew an eye on its leg. Many genes that control development in separate species may have had a common ancestor.

Copyright Pearson Prentice Hall 13-2 Manipulating DNA

Copyright Pearson Prentice Hall The Tools of Molecular Biology How do scientists make changes to DNA? The Tools of Molecular Biology

Copyright Pearson Prentice Hall The Tools of Molecular Biology Scientists use different techniques to: extract DNA from cells cut DNA into smaller pieces identify the sequence of bases in a DNA molecule make unlimited copies of DNA

Copyright Pearson Prentice Hall The Tools of Molecular Biology In genetic engineering, biologists make changes in the DNA code of a living organism.

Copyright Pearson Prentice Hall The Tools of Molecular Biology DNA Extraction DNA can be extracted from most cells by a simple chemical procedure. The cells are opened and the DNA is separated from the other cell parts.

Copyright Pearson Prentice Hall The Tools of Molecular Biology Cutting DNA Most DNA molecules are too large to be analyzed, so biologists cut them into smaller fragments using restriction enzymes. Which type of molecule is an enzyme?

Copyright Pearson Prentice Hall The Tools of Molecular Biology Each restriction enzyme cuts DNA at a specific sequence of nucleotides. Recognition sequences DNA sequence Restriction enzyme EcoR I cuts the DNA into fragments Sticky end

Copyright Pearson Prentice Hall The Tools of Molecular Biology Separating DNA In gel electrophoresis, DNA fragments are placed at one end of a porous gel, and an electric voltage is applied to the gel.

Copyright Pearson Prentice Hall The Tools of Molecular Biology DNA plus restriction enzyme Mixture of DNA fragments Gel Power source Gel Electrophoresis Longer fragments Shorter fragments

Copyright Pearson Prentice Hall The Tools of Molecular Biology First, restriction enzymes cut DNA into fragments. The DNA fragments are poured into wells on a gel. DNA plus restriction enzyme Mixture of DNA fragments Gel Gel Electrophoresis

Copyright Pearson Prentice Hall The Tools of Molecular Biology An electric voltage is applied to the gel. The smaller the DNA fragment, the faster and farther it will move across the gel. Power source

Copyright Pearson Prentice Hall The Tools of Molecular Biology Longer fragments Shorter fragments Gel Electrophoresis Power source

Copyright Pearson Prentice Hall Using the DNA Sequence Making Copies Polymerase chain reaction (PCR) is a technique that allows biologists to make copies of genes. Small amounts of DNA can be multiplied making it easier to analyze. Made possible by an enzyme found in a bacterium living in hot springs in Yellow Stone National Park.

Copyright Pearson Prentice Hall Using the DNA Sequence DNA heated to separate strands PCR cycles DNA copies etc etc. Polymerase Chain Reaction (PCR) DNA polymerase adds complementary strand DNA fragment to be copied