Chapter 11: Regulation of Gene Expression Wasilla High School

Gene Expression is Precisely Regulated  Constitutive genes are actively expressed all the time by every cell  Inducible genes are expressed only when their proteins are needed by the cell  Two types of regulatory proteins (transcription factors) control whether or not a gene is active  Repressor – bind near the promotor to turn a gene off  Activator – bind near the promotor to stimulate transcription

Prokaryotic Gene Regulation  A cluster of genes with a single promoter is called an operon  Can either be inducible or repressible  lac Operon encodes the three lactose (hence lac) metabolizing enzymes in E. coli  Example of negative regulation  Inducible operon  When the enzymes aren't needed a repressor protein can turn transcription off by binding near the operator  An operator is a short DNA sequence near the promotor  When a repressor protein binds to the operator the gene is turned off

Eukaryotic Gene Regulation  Transcription factors bind to promoters to initiate transcription  Approximately 2,000 different transcription factors in humans  Transcription factors occur in different combinations depending on the gene and depending upon if the gene  Some transcription factors are repressors others are enhancers

Epigenetics: Inherited Changes to Gene Expression  Reversible, non-sequential alterations can be made to DNA specifically at promotors  These alterations can be passed down to daughter cells after mitosis or meiosis  Different from mutations because these are reversible changes

Histone Protein Modification  Another form of epigenetics  Histones control gene expression by flagging which portions of DNA are to be unwound and transcribed  Methyl markers repress genes

Chapter 13: Biotechnology

Biotechnology Tools  Recombinant DNA – DNA of one or more organisms added to the DNA of another organism  Restriction Enzymes – cut DNA into fragments that can be manipulated  Gel electrophoresis – DNA separation by size of the fragments  DNA ligase – "tapes" together DNA fragments

Restriction Enzyme Basics  Restriction enzymes cut DNA by finding a specific recognition sequence  Recognition sequences are typically 4 – 6 nucleotides long  Palindromic – opposite strands have the same sequences when read from 5' end  The overhanging ends are called "sticky ends" because they are able to form hydrogen bonds with complementary DNA molecules

Gel Electrophoresis  DNA is cut using restriction enzymes  Samples of the DNA fragments are placed in wells made in a semisolid gel usually made of agarose  An electric current is run through the gel  DNA is negatively charged at its phosphate end so it is attracted to the positive pole at the end of the gel  Small fragments move towards the positive end faster than larger ones creating bands  Tell us about the number of fragments  The sizes of the fragments  The relative abundance of each fragment

Recombinant DNA Can Be Made From DNA Fragments  DNA ligase is used to tape sticky ends together again  Restriction enzymes cut sequences in two separate strands of DNA  By mixing the two appropriately cut strands of DNA this allows recombination to occur  Ligase is added to tape the rejoined pieces together

Goals of Recombination  Cloning  Producing many copies of a particular DNA sequences  Example: using E.coli and other bacteria to create human insulin  Transformation  Transferring desired genes from one organism to another  Antibiotic resistance  These organisms are referred to as transgenic