DNA Replication Packet # Tuesday, November 13, 2018

Historical DNA Discoveries 1928 Federick Griffith finds a substance in heat-killed bacteria that “transforms” living bacteria 1944 Oswald Avery, Cloin MacLeod and Maclyn McCarty chemically identify Griffith’s transforming principle as DNA 1949 Erwin Chargaff reports relationships among DNA bases that provide a clue to the structure of DNA 1953 Alfred Hersey and Martha Chase demonstrate that DNA , not protein, is involved in viral reproduction. Rosalind Franklin produces an x-ray diffraction image of DNA Tuesday, November 13, 2018

Historical DNA Discoveries II 1953 James Watson and Francis Crick propose a model of the structure of DNA. 1958 Matthew Meselson and Franklin Stahl demonstrate that DNA replication is semi conservative replication 1962 James Watson, Francis Crick and Maurice Wilkins are awarded the Nobel Prize in Medicine for discoveries about the molecular structure of nucleic acids. 1969 Alfred Hershey is awarded the Nobel Prize in Medicine for discovering the replication mechanism and genetic structure of viruses Tuesday, November 13, 2018

Homework Assignment Know Griffith’s Transformation Experiments Know The Hershey-Chase Experiments Tuesday, November 13, 2018

Griffith Experiment Tuesday, November 13, 2018

Hershey Chase Experiment Tuesday, November 13, 2018

Nucleotides Nucleotide subunits link together to form a single DNA strand DNA Nucleotides Nucleotides are the building blocks of nucleic acids Phosphate Sugar Deoxyribose Base Purines (Two Rings) Adenine Guanine Pyrimidines (One Ring) Thymine Cytosine Tuesday, November 13, 2018

Nucleotides II Nucleotides are linked together by covalent phosphodiester bonds Each phosphate attaches to the 5’ end of one deozyribose and to the 3’ carbon of the neighboring deoxyribose Makes up the sugar-phosphate backbone Tuesday, November 13, 2018

DNA Strand Tuesday, November 13, 2018

Orientation of DNA Each DNA molecule consists of two polynucleotide chains that associate as a double helix The two chains run antiparallel Tuesday, November 13, 2018

DNA Double Helix Tuesday, November 13, 2018

Base-Pairing Rules for DNA Chargaff Rules Hydrogen bonds hold the chains of the double helix together Adenine forms two hydrogen bonds with thymine Guanine forms three hydrogen bonds with cytosine Chargaff’s rules A always pairs with T G always pairs with C Complementary base pairing Tuesday, November 13, 2018

Chargaff Rules Tuesday, November 13, 2018

Chargaff’s Rules II Tuesday, November 13, 2018

Models of DNA Replication Tuesday, November 13, 2018

Semi-conservative Replication When Ecoli cells are grown for many generations in a medium containing heavy nitrogen, 15N they incorporate the 15N into their DNA. When researchers transfer cells from a 15N medium to a 14N medium and isolate them after either one or two generations, the density of the DNA in each group is what would be expected if DNA replication were semi conservative. In semi conservative replication, each daughter double helix consists of an original strand from the parent molecule and a newly synthesized complementary strand. Tuesday, November 13, 2018

DNA Replication Introduction Tuesday, November 13, 2018

Introduction to the Strands Template Strands {The Parental Strands} Are the strands being copied The original DNA strands During DNA replication, both strands are copied This means that there are TWO template strands Complementary Strands {The Daughter Strands} The NEW DNA strands produced from the Template Strands During DNA replication, there are TWO complementary strands Always remember that the process started with TWO template strands Tuesday, November 13, 2018

Introduction to DNA Replication DNA replication is bidirectional and starts at the origin of replication The process proceeds in both directions from that point. A eukaryotic chromosome may have multiple origins of replication Allows the process to occur faster and more efficient DNA replication/synthesis, of the complementary strands, proceed in a 5’ to 3’ direction. Nucleotides can ONLY be added to the 3’ end. This causes one of the complementary strands to be produced continuously and the other discontinuous The continuous strand is called the leading strand The discontinuous strand is called the lagging strand Is first synthesized as short Okazaki fragments before becoming one strand Tuesday, November 13, 2018

Addition of DNA Nucleotides Tuesday, November 13, 2018

Leading Strand vs. Lagging Strand Tuesday, November 13, 2018

Enzymes of DNA Replication Helicase Unzips DNA double-helix Topoisomerases Prevents tangling and knotting of DNA as the while the strands are unzipped. RNA primase Initiates the formation of “daughter” strands Forms a segment known as the RNA primer The RNA primer contains the nitrogenous base Uracil DNA Polymerase III Enzyme that catalyzes the polymerization (making) of nucleotides Adds Deoxyribonucleotides (nucleotides only found in DNA, as opposed to RNA) to the 3’ end of a growing nucleotide chain Acts at the replication fork DNA Polymerase I A type of DNA polymerase will change the RNA primers into DNA Changing the base Uracil into Thymine Tuesday, November 13, 2018

Enzymes of DNA Replication DNA Ligase Enzyme responsible for joining Okazaki fragments forming the Lagging Strand Gyrase Returns the DNA strands into a Double Helix Zips the DNA back together Tuesday, November 13, 2018

DNA Replication—Lagging Strand Tuesday, November 13, 2018

DNA Replication—The Big Picture Tuesday, November 13, 2018

DNA Excision Repair DNA Polymerase II Tuesday, November 13, 2018

DNA Shortening Tuesday, November 13, 2018

Telomeres & Telomerase End of eukaryotic chromosomes are known as telomeres Short, non-coding, repetitive DNA sequences Shorten each cell cycle but can be extended using the enzyme telomerase Absence of telomerase in certain cells may be the cause of cell aging Cells using their ability to divide after a limited number of cell divisions Most cancer cells have telomerase to maintain the telomeres and possibly resist apoptosis. Tuesday, November 13, 2018