Presentation on theme: "Review Search for genetic material---nucleic acid or protein/DNA or RNA? Griffith’s Transformation Experiment Avery’s Transformation Experiment Hershey-Chase."— Presentation transcript:
1 ReviewSearch for genetic material---nucleic acid or protein/DNA or RNA?Griffith’s Transformation ExperimentAvery’s Transformation ExperimentHershey-Chase Bacteriophage ExperimentTobacco Mosaic Virus (TMV) ExperimentNucleotides - composition and structureDouble-helix model of DNA - Watson & CrickToday’s LessonOrganization of DNA/RNA in chromosomes
2 Search for the genetic material: Stable source of informationAbility to replicate accuratelyCapable of changeTimeline of events:1890 Weismann - substance in the cell nuclei controls development.1900 Chromosomes shown to contain hereditary information, later shown to be composed of protein & nucleic acids.1928 Griffith’s Transformation Experiment1944 Avery’s Transformation Experiment1953 Hershey-Chase Bacteriophage Experiment1953 Watson & Crick propose double-helix model of DNA1956 Gierer & Schramm/Fraenkel-Conrat & SingerDemonstrate RNA is viral genetic material.
3 Frederick Griffith’s Transformation Experiment - 1928 “transforming principle” demonstrated with Streptococcus pneumoniaeGriffith hypothesized that the transforming agent was a “IIIS” protein.
5 Hershey-Chase Bacteriophage Experiment - 1953 Bacteriophage = Virus that attacks bacteria and replicates by invading a living cell and using the cell’s molecular machinery.Structure of T2 phageDNA & protein
7 T2 bacteriophage is composed of DNA and proteins: Set-up two replicates:Label DNA with 32PLabel Protein with 35S3. Infected E. coli bacteria with two types of labeled T24. 32P is discovered within the bacteria and progeny phages, whereas 35S is not found within the bacteria but released with phage ghosts.Hershey-Chase Bacteriophage Experiment1969: Alfred Hershey
8 Gierer & Schramm Tobacco Mosaic Virus (TMV) Experiment - 1956 Fraenkel-Conrat & SingerUsed 2 viral strains to demonstrate RNA is the genetic material of TMV
9 Conclusions about these early experiments: Griffith 1928 & Avery 1944:DNA (not RNA) is transforming agent.Hershey-Chase 1953:DNA (not protein) is the genetic material.Gierer & Schramm 1956/Fraenkel-Conrat & Singer 1957:RNA (not protein) is genetic material of some viruses.
10 Nucleotide = monomers that make up DNA and RNA Three components1. Pentose (5-carbon) sugarDNA = deoxyriboseRNA = ribose(compare 2’ carbons)2. Nitrogenous basePurinesAdenineGuaninePyrimidinesCytosineThymine (DNA)Uracil (RNA)3. Phosphate group attached to 5’ carbon
11 Nucleotides are linked by phosphodiester bonds to form polynucleotides. Covalent bond between the phosphate group (attached to 5’ carbon) of one nucleotide and the 3’ carbon of the sugar of another nucleotide.This bond is very strong, and for this reason DNA is remarkably stable. DNA can be boiled and even autoclaved without degrading!5’ and 3’The ends of the DNA or RNA chain are not the same. One end of the chain has a 5’ carbon and the other end has a 3’ carbon.
13 James D. Watson & Francis H. Crick - 1953 Double Helix Model of DNA Two sources of information:Base composition studies of Erwin Chargaffindicated double-stranded DNA consists of ~50% purines (A,G) and ~50% pyrimidines (T, C)amount of A = amount of T and amount of G = amount of C(Chargraff’s rules)%GC content varies from organism to organismExamples: %A %T %G %C %GCHomo sapiensZea maysDrosophilaAythya americana
14 James D. Watson & Francis H. Crick - 1953 Double Helix Model of DNA Two sources of information:X-ray diffraction studies - Rosalind Franklin & Maurice WilkinsConclusion-DNA is a helical structure withdistinctive regularities, 0.34 nm & 3.4 nm.
15 Double Helix Model of DNA: Six main features Two polynucleotide chains wound in a right-handed (clockwise) double-helix.Nucleotide chains are anti-parallel: 5’ 3’3’ 5’Sugar-phosphate backbones are on the outside of the double helix, and the bases are oriented towards the central axis.Complementary base pairs from opposite strands are bound together by weak hydrogen bonds.A pairs with T (2 H-bonds), and G pairs with C (3 H-bonds).e.g., 5’-TATTCCGA-3’3’-ATAAGGCT-3’Base pairs are 0.34 nm apart. One complete turn of the helix requires 3.4 nm (10 bases/turn).Sugar-phosphate backbones are not equally-spaced, resulting in major and minor grooves.
18 James D. Watson Francis H. Crick Maurice H. F. Wilkins What about? 1962: Nobel Prize in Physiology and MedicineJames D.WatsonFrancis H.CrickMaurice H. F.WilkinsWhat about?Rosalind Franklin
19 Organization of DNA/RNA in chromosomes Genome = chromosome or set of chromosomes that contains all theDNA an organism (or organelle) possessesViral chromosomes 1. single or double-stranded DNA or RNA2. circular or linear3. surrounded by proteinsTMV T2 bacteriophage bacteriophageProkaryotic chromosomes1. most contain one double-stranded circularDNA chromosome2. others consist of one or more chromosomesand are either circular or linear3. typically arranged in arranged in a denseclump in a region called the nucleoid
20 Problem:Measured linearly, the Escherichia coli genome (4.6 Mb) would be 1,000times longer than the E. coli cell.The human genome (3.4 Gb) would be 2.3 m long if stretched linearly.Solutions:Supercoiling DNA double helix is twisted in space about itsown axis, a process is controlled bytopoisomerases (enzymes).(occurs in circular and linear DNA molecules)2. Looped domains
21 More about genome size: C value = total amount of DNA in the haploid (1N) genomeVaries widely from species to species and shows no relationship to structural or organizational complexity.Examples C value (bp) ,502T ,900HIV ,750E. Coli ,639,221Lilium formosanum 36,000,000,000Zea mays 5,000,000,000Amoeba proteus ,000,000,000Drosophila melanogaster ,000,000Mus musculus 3,454,200,000Canis familiaris 3,355,500,000Equus caballus ,311,000,000Homo sapiens 3,400,000,000
22 Eukaryotic chromosome structure Chromatin complex of DNA and chomosomal proteins~ twice as much protein as DNATwo major types of proteins:Histones abundant, basic proteins with a positive chargethat bind to DNA (which is negatively charged)5 main types: H1, H2A, H2B, H3, H4~equal in mass to DNAevolutionarily conservedHistones leave the DNA only transiently during DNA replication.They stay with the DNA during transcription. By changing shapeand position, nucleosomes allow RNA-synthesizing polymerasesto move along the DNA.Non-histones all the other proteins associated with DNA differ markedly intype and structureamounts vary widely
23 Packing of DNA into chromosomes: Level 1 Winding of DNA around histones to create a nucleosome structure.Level 2 Nucleosomes connected bystrands of linker DNA likebeads on a string.Level 3 Packaging of nucleosomes into30-nm chromatin fiber.Level 4 Formation of looped domains.
25 More about different types of DNA you should know about: Centromeric DNA (CEN) Center of chromosome, specialized sequences function with the microtubles and spindle apparatus during mitosis/meiosis.Telomeric DNA At extreme ends of the chromosome, maintain stability, and consist of tandem repeats. Play a role in DNA replication and stability of DNA.
26 Repeated DNA:Unique-sequence DNA Often referred to as single-copy and usually code for genes.Repetitive-sequence DNA May be interspersed or clustered and vary in size.SINEs short interspersed repeated sequences ( bp)LINEs long interspersed repeated sequences (>5,000 bp)Microsatellites short tandem repeats (e.g., TTA|TTA|TTA)