Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Chapter 11DNA: The Molecule of Heredity12So how exactly did we discover that genes are made of DNA??1800’s – we knew that genetic information is contained in units called “genes”1900’s – we knew that genes are part of chromosomesThen we discovered that chromosomes consist of only DNA and proteins11.1311.1So how exactly did we discover that genes are made of DNA??In the 1920’s Griffith was trying to make a vaccine against pneumonia (a bacteria)411.1Fig 11.1511.1So how exactly did we discover that genes are made of DNA??What was the genetic material transferred from one bacteria to another?Remember chromosomes consist of DNA and proteinProtein is denatured by heat so maybe the DNA is not damaged and can be transferred?Many scientists were skeptical…6So how exactly did we discover that genes are made of DNA??Another group showed that bacteria can take upDNA from their externalenvironmentPeople were still skeptical(it takes a lot to convincea scientist)Fig 11.211.17So how exactly did we discover that genes are made of DNA??Finally Hershey and Chaseperformed a set of experiments that were very convincingBacteriophages are viruses thatinfect bacteria•Composed of only DNA And protein11.18So how exactly did we discover that genes are made of DNA??DNA contains phosphorusProtein contains sulfurSo DNA is the geneticMaterial!!!11.19OK, so then how did we discover the structure of DNA? Wilkins and Franklin – used X-ray diffraction (shot X-rays at DNA molecules and recorded how it bounced off)•DNA is long and thin•DNA has a uniform diameterof 2 nanometers•DNA is helical•DNA consists of repeatingsubunits11.2Fig 11.410OK, so then how did we discover the structure of DNA? Watson and Crick took this information and simply thought about itThe structure of DNA was Solved at the eagle pub inCambridge, England in1953Fig E11-311.211DNA is composed of two nucleotide strands wound into a double helixNucleotide (chapter 3):•Phosphate group•Sugar (deoxyribose in DNA)•Nitrogen-containing base11.2Fig 11.312The structure of DNAEach nucleotide strand has:•Sugar phosphate backbone•5’ free phosphate•3’- free sugarThe bases face inward and hydrogen bond with each other11.25’5’3’3’Fig 11.513The structure of DNAThe DNA double helix•The nucleotide strands areantiparallel•Complementary base pairshydrogen bond•A-T•G-CChargaff’s rule- a DNA strand contains equal amounts of A and T, and equal amounts of G and C5’5’3’3’11.2Fig 11.5Know the numbers for which it travels1411.2Fig 11.515DNA encodes information within the sequence of nucleotidesThere are four different nucleotides (A, T, G, and C)The order of nucleotides can be “read” just like the order of letters make up wordsMore in chapter 12 11.316 DNA replication is essential for cell divisionOccurs during S phase of interphaseDNA replication produces two identical DNA double helices from one parental double helixBase pairing (A-T, and G-C) is the foundation of DNA replication11.417DNA replicationIn order to replicate DNA you need three things:•Parental DNA strands•Free nucleotides (synthesized in the cell)•Specialized enzymes that unwind the parental DNA double helix and synthesize new DNA strands11.4Fig 11.618DNA replicationDNA replication can be broken down into three steps1.) DNA helicase separates the parental DNA strands2.) DNA polymerase synthesizes new DNA strands3.) DNA ligase joins the new segments of DNA11.4Fig 11.619DNA replication: DNA helicases separate the parental DNA strands 11.4Fig E11.7•DNA helicases form a replication “bubble”•Each replication bubble contains two replication “forks”20DNA replication: DNA polymerase synthesizes new DNA strands11.4Fig E11.7•Free nucleotides are matched to bases on parental strands by DNA polymerase to form daughter DNA polymers (DNA strands)•Remember base pairing!21DNA replication: DNA polymerase synthesizes new DNA strands11.4Fig E11.4Synthesis of DNA ALWAYS occurs in the 5’ -> 3’ directionNeed the 3’ hydroxyl group to attach the new nucleotide22DNA replication: DNA polymerase synthesizes new DNA strands11.4Fig E11.7Synthesis is ALWAYS 5’-> 3’So the parent strand is ALWAYS read 3’->5’ by DNA polymerase23DNA replication: DNA polymerase synthesizes new DNA strands11.4Fig E11.7•The continuous daughter strand is called the leading strand•The discontinuous strand is called the lagging strand•Discontinuous pieces are called okazaki fragments24DNA polymerase #1DNApolymerase #3DNA polymerase #2 4533535Lagging strandLeading strandDNA HelicaseOkazaki fragments11.4 Fig E11.725DNA replication: DNA ligase joins the sections of daughter DNA together11.4Fig E11.726DNA replication is semiconservative*Semiconservative replication 11.4Fig 11.7•Conserves one parental strand•Produces one new strand27Mutations are changes in the sequence of bases in DNADNA replication is highly accurate•DNA contains errors only every 100 million to 1 billion base pairs•This is less than one, per chromosome, per replicationCertain enzymes “proofread” DNA during and after synthesis11.52811.5Mutations are changes in the sequence of bases in DNAHowever, mistakes do happenMutations can occur during replication and can be caused by a variety of environmental conditionsMost are fixed but not all29Mutations range from changes in single base pairs to large differencesNucleotide substitutions (point mutations)•One base pair is replacedWith another one11.5Fig 11.830Mutations range from changes in single base pairs to large differencesInsertion mutation11.5Fig 11.8•One or more nucleotide pairs are inserted into the DNA double helix31Mutations range from changes in single base pairs to large differencesDeletion mutation11.5Fig 11.832Mutations range from changes in single base pairs to large differencesInversion•When a piece of DNA is cut out of a chromosome and turned around before reinsertion11.5Fig 11.833Mutations range from changes in single base pairs to large differencesTranslocation•When a piece of DNA is removed from one chromosome and attached to another11.5Fig 11.834Mutations have varying effectsAn enzyme called myostatin controls the size
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