Bellwork: How is gene regulation in prokaryotes and Eukaryotes similar Bellwork: How is gene regulation in prokaryotes and Eukaryotes similar? How is it different?

Gene regulation and expression Section 13.4

Gene regulation and expression Why is gene regulation important? Why do cells regulate which genes are used at a given time?

Prokaryotic gene regulation Bacteria and prokaryotes do not need all of their genetic information transcribed at once They only want to use the genes necessary for the cells to function This allows bacteria to respond to changes in their environment This is done through DNA binding protein, which regulate genes by controlling transcription Some switch genes on, some turn them off

Operons An operon is a group of genes that are regulated together Genes will have related functions E-coli for example has 4238 genes 3 genes are clustered together, which allow the bacterium to use the sugar lactose as food These 3 lactose genes are called the lac operon.

Promoters and operators On one side of the operon’s three genes are two regulatory regions Promoter: Site where RNA polymerase can bind Operator: When a DNA binding protein called a repressor binds to DNA

The lac operon in e-coli Lactose turns the operon on

Eukaryotic gene regulation Most of the principles of gene regulation in prokaryotes also apply to eukaryotes Most eukaryotic genes are however controlled individually, and have more complex regulatory sequences than with e-coli. TATA box helps with DNA transcription Made of 25 – 30 base pairs containing the sequence TATATA or TATAAA Bind a protein that helps position RNA polymerase

Transcription factors Transcription factors bind to DNA sequences in the regulatory regions of eukaryotic genes, and control the expression of the gene Some enhance transcription by: Open up tightly packed chromatin Attract RNA polymerase Others block access to genes, much like repressor proteins Normally multiple transcription factors are required before RNA polymerase can bind to the DNA

Promoters in Eukaryotes Promoters have multiple binding sites for transcription factors Certain factors can activate scores of genes at once, changing patterns of gene expression Other factors only respond to chemical signals Steroid hormones are chemical messengers that enter the cell and bind to receptor proteins These receptor complexes act as transcription factors, so one single chemical signal can activate multiple genes The exit of mRNA from the nucleus, the stability of mRNA and the breakdown of a gene’s protein s can all also act as a regulating factor

Cell specialization Everything is more complicated in Eukaryotes – why? Our DNA contains the information for every cell in our body Would liver enzymes need to be produced in your bone marrow? Keratin, a protein in hair follicles is not produced in blood cells, or your heart, lungs… Cell specialization requires genetic specialization Complex gene regulation makes this possible

RNA interference Cells contain a lot of small RNA molecules that are unrelated to the three major groups of RNA These small RNA molecules help regulate gene expression They interfere with mRNA Interference RNA molecule produce by transcription, produces double stranded hairpin loop Dicer enzyme make small fragments of miRNA miRNA attaches to proteins and forms silencing complex

RNA interference continued RNA interference has made it possible for researchers to switch genes on and off at will All they had to do was insert double stranded RNA Can be used to study gene expression in the lab. Holds the potential to cures for cancer and viruses, allowing us to treat currently incurable diseases

Genetic control of development What controls the development of cells and tissues? In a multicellular organism, all of the specialized cell types came from the same fertilized egg cell How do the cells know which cell to become? Cells undergo differentiation, and become specialized in structure and function as they develop Studying genes that control development and differentiation is an exciting area of Biology

Homeotic genes Edward B Lewis showed that specific groups of genes control the identity of body parts in the embryo of fruit fly By mutating one of these genes, it was possible to have a fly with a leg growing out of it’s head His work showed that there are a set of master control genes (Homeotic genes) that regulate organ development in specific parts of the body

Homeobox and Hox genes Homeotic genes share a very similar 180 base DNA sequence – a homeobox Homeobox genes code for transcription factors that activate other genes important for cell development and differentiation Homeobox genes are expressed in certain regions In flies, a group of homeobox genes, called HOX genes are located side by side in a cluster These determine the identity of each segment of a flie’s body Arranged in the exact order they ate expressed in the body

Hox genes This does not apply just to flies Nearly all animals fit this rule Master control genes are like switches that trigger particular patterns of development and differentiation in cells and tissues Evidence that genes have descended from common ancestors

Environmental influences Environment can play a role in cell gene expression Temperature, nutrients, salinity for example can all effect gene expression Metamorphosis of tadpoles to frogs – great example Mixture of environmental and hormonal factors Speed of metamorphosis can be influenced by environmental factors, which translate into hormonal changes. Hormones function at molecular level