BIOL 3451 1st Edition Lecture 20 Outline of Last Lecture I. 15.2 Spontaneous Mutations Arise from Replication Errors and Base ModificationsII. 15.3 Induced Mutations Arise from DNA Damage Caused by Chemicals and RadiationIII. 15.4 Single-Gene Mutations Cause a Wide Range of Human DiseasesIV. 15.5 Organisms Use DNA Repair Systems to Counteract MutationsOutline of Current Lecture I. 15.5 Organisms Use DNA Repair Systems to Counteract MutationsII. 15.6 The Ames Test Is Used to Assess the Mutagenicity of CompoundsIII. 15.7 Geneticists Use Mutations to Identify Genes and Study Gene FunctionIV. 15.8 Transposable Elements Move within the Genome and May Create Mutations V. 16.1 Prokaryotes Regulate Gene Expression in Response to Environmental ConditionsVI. 16.2 Lactose Metabolism in E. coli Is Regulated by an Inducible SystemVII. 16.3 The Catabolite-Activating Protein (CAP) Exerts Positive Control over the lac OperonCurrent LectureI. 15.5 Organisms Use DNA Repair Systems to Counteract Mutationso Xeroderma pigmentosum (XP): rare genetic disorder that affects NER pathway and doesn’t fix mutations from radiation, and other mutagens  Severe skin abnormalities, skin cancers, wide range of other symptoms like developmental and neurological defects (these enzymes also play a role in nervous system) Have a 2000 fold higher rate of cancero NER pathway defects give rise to two other autosomal recessive diseases Cockayne syndrome (CS)- Developmental and neurological defects, sunlight sensitivity, but no increase in cancers- Premature aging and death by age 20- When in 20s, look like they are in their 60s Trichothiodystrophy (TTD)- Dwarfism, retardation, brittle hair and skin, facial deformities- Sensitivity to sunlight but no increase in cancers- Median life span of six yearsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Exposure to ionizing radiation can lead to both strands of DNA being cleaved, results in chromosomal rearrangements leading to cancer or cell deatho Double-strand break repair (DSB repair): reattaches two broken DNA strands Homologous recombination repair: during late S or early G2 phase of cellcycle- Can fix by winding two strands together- Fig 15.16 Nonhomologous end joining: activated in G1II. 15.6 The Ames Test Is Used to Assess the Mutagenicity of Compoundso Ames test: uses number of different strains (mutant-auxotroph) of Salmjonella typhimurium selected for their ability to reveal the presence of specific types of mutations Used in development of industrial and pharmaceutical compounds Trying to figure out what causes cancers, and get rid of it You can mutate a mutant (try and reverse the mutant and fix it)=called a reversion Many known carcinogens have been shown by the Ames test to be a strong mutagens (why it causes cancer)- Cigarettes have over 60 compounds that test positive in Ames test Fig. 15.17III. 15.7 Geneticists Use Mutations to Identify Genes and Study Gene Functiono Geneticists often induce mutations to identify genes and processes that regulate biological functions Short generation time Produce abundant progeny Readily mutagenized and crossed Hard to do with vertebrates (too many social groups fighting for their rights)o Ionizing radiation used to create chromosomal breaks, deletions, and translocations Ethyl methansulfonate (EMS) and nitrosoguanidine cause single base-pair changes, deletions, and insertions- Have to sequence whole genome to figure out which gene the alkyl group was added to (doesn’t take long now-about 1 min) Transposons use transposons to create mutations by inserting into a gene coding or regulatory region- Can screen for the gene that has the transposono Genetic screen: involves visual or biochemical examination of large numbers of mutagenized organismsIV. 15.8 Transposable Elements Move within the Genome and May Create Mutationso Transposable elements: (transposons) can insert themselves into various locations within the genome DNA element which is able to replicate itself and insert itself into organisms and stay there; precise functions still unknowno Bacteria have two type of transposons: Insertion sequence (IS elements)- Can move from one location to another- If inserted into a gene/gene-regulatory region, can cause mutations Bacterial transposons- Larger than IS elements- Can introduce multiple drug resistance onto bacterial plasmids (R factors)o Plasmids are very mobile and spreading multiple drug resistance between bacterial strainso Two mutations, Dissociation (Ds) and Activator (Ac) are transposable elements in corn Movement of Ds gene is dependent on the Ac geneo More than 30 families of transposable elements are found in Drosophilao Approximately half of the human genome is composed of transposable element DNA Most human transposons appear to be inactiveo It is possible for a mobile element to transpose from one chromosome to another in gamete-forming cells of the mother, causing a genetic diseaseo Inserted transposons can disrupt normal gene function in various ways, resulting in phenotypic changes or diseaseo Due to their ability to alter genes and chromosomes, transposons may contributeto the variability that underlies evolutionV. 16.1 Prokaryotes Regulate Gene Expression in Response to Environmental Conditionso Gene regulation been studied extensively in E. colio Highly efficient genetic mechanisms have evolved because their life cycle is so short turn transcription of specific genes on and off depending on a cell's metabolic need for specific gene products (use one that is “most efficient”) these responses can be due to changes in environment as well as nonenvironmentally regulated cellular activity (cell changes) and cell divisiono Bacteria adapt to their environment by producing certain enzymes (inducible enzymes) only when specific substrates are present (done only during certain conditions)o Enzymes continuously produced regardless of chemical makeup of the environment are called constitutive enzymes  Make constantly at same level, doesn’t necessarily mean you make a lot of it Need all the time no matter whato An abundance of an end product in the environment represses gene expression of it (repressible system)o Common type of regulation (inducible or repressible) can be under positive