2 GriffithStreptococcus pneumoniae - bacteria that causes pneumonia in mammalsR strain – harmlessS strain – pathogenicmixed heat-killed S strain with live R strain bacteria and injected this into a mousethe mice died
3 Transformationchange in genotype and phenotype due to the assimilation of a foreign substance (now known to be DNA) by a cell.
4 Avery and other scientists discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation of an organism to the next.Oswald Avery 1944World knows a molecule carries the genetic information.Doesn’t know if the molecule is a: protein, lipid, carbohydrate, RNA, or DNAAvery performs Griffith’s experiment again with a twist.
5 What is the transforming substance? Track the infection of bacteria by virusesViruses consist of a DNA enclosed by a protective coat of proteinTo replicate, a virus infects a host cell and takes over the cell’s metabolic machinery
6 Bacteriophages (phage) Virus that specifically attacks bacteria
7 Hershey and ChaseT2 phage, consisting almost entirely of DNA and protein, attacks Escherichia colilabel protein and DNA and then track which entered the E. coli cell during infection
8 How? Grew one batch of T2 phage in the presence of radioactive sulfur marking the proteins but not DNAGrew another batch in the presence of radioactive phosphorusmarking the DNA but not proteinsAllowed each batch to infect separate E. coli cultures
10 ChargaffDeveloped a series of rules based on a survey of DNA composition in organismsDNA is a polymer of nucleotidesconsists of a nitrogenous base, deoxyribose, and a phosphate groupThe bases = adenine (A), thymine (T), guanine (G), or cytosine (C).The four bases are found in ratios
11 Wilkins and FranklinX-rays are diffracted as they passed through aligned fibers of purified DNAUsed to deduce the three-dimensional shape of molecules
18 Human CellsCopy its billion base pairs and divide into daughter cells in a few hoursOne error per billion nucleotides
19 Origin of ReplicationSingle specific sequence of nucleotides that is recognized by replication enzymesenzymes separate the strands, forming a replication “bubble”Replication proceeds in both directions until the entire molecule is copied
20 Anti-Parallel Each DNA strand has a 3’ end with a free hydroxyl group attached to deoxyribose and a5’ end with a free phosphate group attached to deoxyribose.
23 DNA polymerases can only add nucleotides to the free 3’ end of a growing DNA strand leading strand - used by polymerases as a template for a continuous complimentary strandlagging strand - copied away from the fork in short segments (Okazaki fragments)
24 DNA polymerase and Primers Polymerase cannot initiate synthesis of a polynucleotidecan only add nucleotides to the end of an existing chainTo start a new chain requires a primera short segment of RNA
28 Mismatched nucleotides Reactive chemicals, radioactive emissions, X-rays, and ultraviolet light can change nucleotides in ways that can affect encoded genetic informationEach cell continually monitors and repairs its genetic materialover 130 repair enzymes identified in humans
29 In mismatch repair, special enzymes fix incorrectly paired nucleotides In nucleotide excision repair, a nuclease cuts out a segment of a damaged strand
30 telomeres = The ends of eukaryotic chromosomal DNA molecules – long repetitive sequences (no genes)
31 Telomeraseuses a short molecule of RNA as a template to extend the 3’ end of the telomere
32 Difference between bacterial chromosomes and eukaryotic chromososes
34 Nucleosomes, or “beads on a string” (10-nm fiber) Fig aNucleosome(10 nm in diameter)DNA double helix (2 nm in diameter)H1Histone tailHistonesFigure 16.21a Chromatin packing in a eukaryotic chromosomeDNA, the double helixHistonesNucleosomes, or “beads on a string” (10-nm fiber)