dna structure and function chapter 13. dna deoxyribonucleic acid

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DNA Structure and Function Chapter 13 Slide 2 DNA Deoxyribonucleic Acid Slide 3 Slide 4 Slide 5 Impacts, Issues Cloning DNA can lead to problems for the cloned offspring Slide 6 Fig. 13-1a, p.206 Slide 7 Fig. 13-9, p.214 Dolly lived for 6 years - Slide 8 Slide 9 Slide 10 Nucleus being injected into a donor cell whose nucleus was removed Slide 11 This Yellow lab Died of Cancer Owners Were so Sad Slide 12 So they cloned him Slide 13 It cost them $155,000 Slide 14 13.1 The Hunt for DNA Investigations that led to our understanding that DNA is the molecule of inheritance reveal how science advances Slide 15 The proof that DNA is the carrier of Genetic information was made by: Watson and Crick Wilkins Rosalind Franklin Avery-MacLeod-McCarty Hershey-Chase Slide 16 How was DNA linked to heredity? The role of DNA in heredity was discovered by studying bacteria and the viruses that infect them. Viruses that infect bacteria are called bacteriophages Slide 17 1 Mice injected with live cells of harmless strain R 2 Mice injected with live cells of killer strain S 3 Mice injected with heat-killed S cells 4 Mice injected with live R cells plus heat- killed S cells Mice die. Live S cells in their blood Mice dont die. No live R cells in their blood Mice die. Live S cells in their blood Mice dont die. No live S cells in their blood Fig. 13-3, p.208 These cells were transformed by some type of Substance what was that substance? Slide 18 Oswald Avery Experiment Identified the transformed substance He looked at: proteins, RNA and DNA to see which one contained the genetic information. He heat killed one at a time until he figured it was DNA Avery and partners McCarty and MacLeod announced: transforming substance is DNA Slide 19 Avery, McCarty and MacLeod people were skeptical about their findings because: DNA too simple to be genetic material Proteins way more complicated so were thought to be genetic material Didnt know a lot about DNA at the time Slide 20 Hershey and Chase Experiments Used bacteriophages Viruses very simple: protein and DNA (or RNA) Looked at a bacteriophage that infects E. coli. So which viral component: protein or DNA? They radiolabeled protein with sulfur They radiolabeled DNA with phosphorus Slide 21 Fig. 13-4c1, p.209 T2 virus Bacteriophage That infects E. Coli Slide 22 Fig. 13-4c2, p.209 Slide 23 virus particle labeled with 35 S DNA (blue) being injected into bacterium 35 S remains outside cells virus particle labeled with 32 P DNA (blue) being injected into bacterium 35 P remains inside cells Fig. 13-4ab, p.209 Slide 24 Discoveries 1944 - Avery, McCarty and MacCloed figured out that DNA was the transformation factor in pathogens injected in mice 1952 - Hershey and Chase looked at bacteriophages and found that DNA is the genetic component Now that the genetic component (DNA) has been identified, what about its structure? Slide 25 13.2 The Discovery of DNAs Structure Watson and Cricks discovery of DNAs structure was based on almost fifty years of research by other scientists Slide 26 DNA Structure Wilkins and Rosalind Franklin London Rosalind Franklin developed an Xray diffraction technique in Wilkins lab, where Crick also studied Watson visited Wilkins lab and saw Franklins work and the images she came up with He figured out from these images that DNA is a double helix Slide 27 DNA structure So, Watson and Crick used Rosalind Franklins x-ray crystalography diffraction image to determine the shape of DNA They read one of Franklins unpublished studies where she figured out that the sugar phosphate is part of the DNA backbone, with the hydrophobic nitrogenous bases in the center 1953 published a 1 page paper on the structure of DNA Slide 28 Fig. 13-2, p.207 Slide 29 DNAs Building Blocks Nucleotide A nucleic acid monomer consisting of a five- carbon sugar (deoxyribose), phosphate group, and one of four nitrogen-containing bases DNA consists of four nucleotide building blocks Two pyrimidines: thymine and cytosine Two purines: adenine and guanine Slide 30 sugar (deoxyribose) adenine A base with a double-ring structure guanine (G) base with a double-ring structure cytosine (C) base with a single-ring structure thymine (T) base with a single-ring structure Fig. 13-5, p.210 Slide 31 p.211 Slide 32 2-nanometer diameter overall 0.34-nanometer distance between each pair of bases- 10 bases in each twist Fig. 13-6, p.211 Slide 33 Fig. 13-7, p.212 Slide 34 Slide 35 Enzymes Involved DNA polymerase Ligase RNA polymerase Helicase Topoisomerase Slide 36 DNA Replication in short: Step 1: DNA is unwound at a replication fork by helicases that unwind and untwist DNA Step 2: single strand binding proteins bind to the upaired strands to keep them separated and stabilized The DNA can get twisted behind the replication fork so Step 3: Topoisomerase binds and unbinds ahead of the replication fork to alleviate the tension Slide 37 DNA replication in short Step 4: primase starts a new strand but its not a DNA strand. Its an RNA strand 5 10 nucleotides long. Step 5: the new DNA strand will start from the 3 prime end of this RNA primer. So, RNA polymerase starts the process but DNA polymerase takes over and adds a DNA strand onto the RNA primar Slide 38 DNA Replication in short Step 6: Ligase attaches new nuceotides together at the sugar phosphate backbones Slide 39 Table 13-1, p.212 Slide 40 Enzymes of DNA Replication DNA helicase Breaks hydrogen bonds between DNA strands DNA polymerase Joins free nucleotides into a new strand of DNA DNA ligase Joins DNA segments on discontinuous strand Slide 41 DNA Replication Fig. 13-8a, p.213 Stepped Art Slide 42 DNA Replication DNA is antiparellel and undergoes semiconservative replication Slide 43 As Reiji Okazaki discovered, strand assembly is continuous on just one parent strand. This is because DNA synthesis occurs only in the 5 to 3 direction. On the other strand, assembly is discontinuous: short, separate stretches of nucleotides are added to the template, and then enzymes fill in the gaps between them. Fig. 13-8b, p.213 Slide 44 Why the discontinuous additions? Nucleotides can only be joined to an exposed OH group that is attached to the 3 carbon of a growing strand. Fig. 13-8c, p.213 Slide 45 Slide 46 Lagging Strand uneven Okazaki fragments cause a problem at the end of the DNA strand Slide 47 Slide 48 Antiparellel semiconservative replication DNA polymerases can only add nucleotides to the free 3 prime end never 5 prime end So, DNA can only elongate in the 5 3prime direction One strand is the leading strand continuous replication Slide 49 The other strand is the lagging strand discontinuous replication So it has to replicate in sections away from the replication fork These fragments are called Okazaki fragments Slide 50 Chargaffs Rules The amounts of thymine and adenine in DNA are the same, and the amounts of cytosine and guanine are the same: A = T and G = C The proportion of adenine and guanine differs among species Slide 51 Franklin, Watson and Crick Rosalind Franklins research in x-ray crystallography revealed the dimensions and shape of the DNA molecule: an alpha helix This was the final piece of information Watson and Crick needed to build their model of DNA Slide 52 Watson and Cricks DNA Model A DNA molecule consists of two nucleotide chains (strands), running in opposite directions and coiled into a double helix Base pairs form on the inside of the helix, held together by hydrogen bonds (A-T and G-C) Slide 53 Patterns of Base Pairing Bases in DNA strands can pair in only one way A always pairs with T; G always pairs with C The sequence of bases is the genetic code Variation in base sequences gives life diversity Slide 54 13.2 Key Concepts Discovery of DNAs Structure A DNA molecule consists of two long chains of nucleotides coiled into a double helix Four kinds of nucleotides make up the chains, which are held together along their length by hydrogen bonds Slide 55 13.3 DNA Replication and Repair A cell copies its DNA before mitosis or meiosis I DNA repair mechanisms and proofreading correct most replication errors Slide 56 Semiconservative DNA Replication Each strand of a DNA double helix is a template for synthesis of a complementary strand of DNA One template builds DNA continuously; the other builds DNA discontinuously, in segments Each new DNA molecule consist of one old strand and one new strand Slide 57 Checking for Mistakes DNA repair mechanisms DNA polymerases proofread DNA sequences during DNA replication and repair damaged DNA When proofreading and repair mechanisms fail, an error becomes a mutation a permanent change in the DNA sequence Slide 58 13.3 Key Concepts How Cells Duplicate Their DNA Before a cell begins mitosis or meiosis, enzymes and other proteins replicate its chromosome(s) Newly forming DNA strands are monitored for errors Uncorrected errors may become mutations Slide 59 13.4 Using DNA to Duplicate Existing Mammals Reproductive cloning is a reproductive intervention that results in an exact genetic copy of an adult individual Slide 60 1 A microneedle is about to remove the nucleus from an unfertilized sheep egg (center). 2 The microneedle has now emptied the sheep egg of its own nucleus, which held the DNA. 3 DNA from a donor cell is about to be deposited in the egg. 4 An electric spark will stimulate the egg to enter mitotic cell division. the first cloned sheep Fig. 13-9, p.214 Slide 61 Table 13-2, p.214 Slide 62 Cloning Clones Exact copies of a molecule, cell, or individual Occur in nature by asexual reproduction or embryo splitting (identical twins) Reproductive cloning technologies produce an exact copy (clone) of an individual Slide 63 Reproductive Cloning Technologies Somatic cell nuclear transfer (SCNT) Nuclear DNA of an adult is transferred to an enucleated egg Egg cytoplasm reprograms differentiated (adult) DNA to act like undifferentiated (egg) DNA The hybrid cell develops into an embryo that is genetically identical to the donor individual Slide 64 Therapeutic Cloning Therapeutic cloning uses SCNT to produce human embryos for research purposes Researchers harvest undifferentiated (stem) cells from the cloned human embryos Slide 65 13.4 Key Concepts Cloning Animals Knowledge about the structure and function of DNA is the basis of several methods of making clones, which are identical copies of organisms Slide 66 13.5 Fame and Glory In science, as in other professions, public recognition does not always include everyone who contributed to a discovery Rosalind Franklin was first to discover the molecular structure of DNA, but did not share in the Nobel prize which was given to Watson, Crick, and Wilkins Slide 67 Rosalind Franklins X-Ray Diffraction Image Franklin died of cancer at age 37, possibly related to extensive exposure to x-rays Slide 68 13.5 Key Concepts The Franklin Footnote Science proceeds as a joint effort; many scientists contributed to the discovery of DNAs structure