BIOLOGY 305 1st Edition Lecture 15 Outline of Last Lecture I. BDM ModelII. UPGMA Analysis using Distance MatricesIII. Molecular ClockIV. Evolutionary TreesOutline of Current Lecture I. Introduction to Genetic InformationII. DNA as the Source of Genetic InformationA. Nucleotide Building BlocksB. Helical StructureIII. SupercoilingIV. More about Genetic MaterialV. Sample QuestionsCurrent LectureI. Introduction to Genetic InformationWhat three aspects define genetic information?- The ability to hold information (to code for an entire organism!)- The ability to replicate (able to be faithfully copied for each cell in the organism)- The ability to mutate (provide material for evolutionary selection)Transformation – the change in expression do to the change in DNAEx: Griffith’s Experiment: A virulent strain of bacteria (S) results in dead mice but (R)-strain injections results in live mice. If the (S) bacteria are boiled/destroyed and (R) is live, the mice live. But if the boiled (S) strain in addition to the R strain exists in the mice, the mice are killed.Concluded that the S strain somehow transforms R to become virulentCan conclude that transforming molecule must be DNA, thus which mice would beexpected to survive?The mice with destroyed DNA will survive because the transforming molecule is eliminatedHow was DNA discovered to be the source of genetic information?Hershey-Chase Experiment: Radioactively labeled protein in comparison to labeled DNA in bacteriophages showed that only DNA was injected into bacterial cells by the bacteriophageII. DNA as the Source of Genetic InformationOne of the dogmas of biology is structure vs. function, and the study of DNA as the encoder of genetic information will greatly exemplify thisA. Nucleotide Building Blocks4 Nucleotide Building Blocks:The purines - Adenine (A), Guanine (GThe pyrimidines - Cytosine (C) and Tyrosine (T)A nucleoside consists of a pentose ring (ribonucleic acid), a base (purine or pyrimidine), a glycosidic bond, a 2’ OH group if it is RNA or an H group if it is DNA. A nucleotide marks the attachment of 5’ phosphate groups (attached to the 1’ carbon) which attaches to the 3’ carbon of the ribose in the NEXT nucleotide via a phosphodiester bond.Chargaff’s Rules:The relative amounts of various bases in DNA results in these rules about base concentration:A = T (A pairs with T, so there should be equal concentrations of the two)2 hydrogen bonds pair these together, so their interaction is relatively weakerG = C (same applies to G and C)3 hydrogen bonds pair these together, so their interaction is relatively strongerA + T =/= G + C (but the concentration of A/T can be different from that of G/T)B. Helical StructureX-Ray Diffraction of DNARosalind Franklin Experiment: The view angle of a cross-section of DNA: Conclusion: DNA is long, skinny, helical, containing parallel structuresThe spots lead to the discovery of the DNA Helix Structure, by Watson and Crick DNA is…1) Double-stranded helix2) Right handed3) Antiparallel – the two strands run in the opposite directions of each other4) 10 base pairs per turn, ~34 A (with the distance between each ladder about 3.4 A5) Has a major and minor groove – which is important for DNA binding proteinsSome of which are sequence specific, others are not6) Is really long (1.9 m total in the average human!)7) Can form supercoilsWhat are the impacts of DNA structure on nature?Directly impacts: molecular nature of genes, replication, and mutationIndirectly impacts: genetic code, gene expression, and developmentVery long-run: genomes and our understanding of lifeWhat some discoveries facilitated by DNA structure?Heredity, drug synthesis, cancer, GMOs, personal genomics, Crime investigation, Development, PCR, Cloning, and moreIII. SupercoilingWhen DNA has a free end, in order to be unwound by 10 DNA base pairs, the DNA helix must rotate by one turnWhen DNA’s ends are fixed, and this unwinding by 10 BPs results in one supercoilWhen the helix opening is facilitated (aka encouraged), the DNA under goes negative supercoiling. When the helix opening is hindered, the DNA under goes positive supercoilingIV. More about Genetic MaterialWhat are some of the exceptions to DNA as a genetic material?1) Viruses have RNA as their genomes2) Prions are infection proteins that act as genetic material and cause brain diseasesGenomes are all the genetic information of organismsGenome size does not necessarily relate to organism complexityHowever, the number of cell developmental complexity doesCRISPR (clustered regularly interspaced short palindromic repeats) – comprises the bacterial immune system, they have sequence similarity to bacteriophages, facilitates RNA-guided, site specific DNA cleavageEx: Say we know that…If the live R strain is added to a CRISPR with an S sequence, and the S strain is boiled, themouse will surviveV. Vocabulary and Sample Questions1) As an investigator at the Center for Disease Control, you are characterizing nucleic acids found in five new types of viruses. For each virus indicate whether it is likely to be single stranded (ss) or double stranded (ds), and if it is composed of DNA or of RNA. Which of the following is an ss RNA virus?2) How long is human DNA (all chromosomes, diploid genome)?A. 0.2 µmB. 0.34 cmC. 22 cmD. 1.9 mE. 2.7 kmANSWERS:1. DFirst of all, RNA has U bases in place of TSo A, B & E are false because they are DNASecondly, Virus 3 is most likely to be double-stranded because it most closely follows Chargaff’s Rules, in which base pair concentration is identical to its complement, thus complementarity suggests double-strandednessThus, virus 4 is a single-stranded RNA virus2. D, the human genome is 1.9 m