DNA Structure & Replication (Outline)
DNA Structure & Replication (Outline) Historical perspective (DNA as the genetic material): Genetic transformationDNA as the transforming agentDNA is the genetic material in bacterial viruses (phage)Historical perspective (Structure of DNA):Identifying ribose and deoxy ribose Equal parts of nucleotide parts The base-pairing rule DNA structure: double stranded anti-parallel strands DNA structure: helixBasis for polarity of SS DNA and anti-parallel complementarystrands of DNAModels of DNA replicationMechanism of DNA replication: steps and molecular machineryFidelity of DNA replication 1
Genetic Material“A genetic material must carry out two jobs:duplicate itself and control the development ofthe rest of the cell in a specific way.”- Francis Crick, 1953NucleusDNACell2
The Road to the Double Helix3
History leading to establishing DNA as thegenetic materialFriedrich Miescher, 1871- Swiss physician and biochemist- Isolated white blood cell nuclei from pusooAcid substance with nitrogen and phosphorus“Nuclein” later changed into nucleic acid4
History of DNAArchibald Garrod, 1902- English physician- Linked inheritance of“inborn errors ofmetabolism” with the lackof particular enzymes- First described thedisease alkaptonuria5
History of DNAFrederick Griffith, 1928- English microbiologist- Established the concept of transformation:a change in genotype (genetic makeup) by aforeign substance that changes the phenotype(observed properties or trait)6
Frederick GriffithWorked with Diplococcus pneumonia, which exists intwo typesoType S (Smooth) Produces capsuleoType R (Rough) No capsuleoCapsule associated with virulence (causing disease)7
Discovery of Bacterial TransformationFigure 9.1Figure 9.18
History of DNAAvery, MacLeod, and McCarty, 1944- American physicians- DNA is the transforming material(Can convert Type R bacteria into S)9
The Transforming PrincipleFigure 9.1Figure 9.210
History of DNAAlfred Hershey and Martha Chase, 1953 American microbiologists Viruses can infect E. coli bacteria A virus in not a cell, it has protein “head” and DNAcore Can replicate only using host living cells as host DNA is the genetic material of these viruses11
Discovering the Structure of DNAPhoebus Levine- Russian-American biochemist- Identified the 5-carbon sugars ribose in 1909and deoxyribose in 1929- Discovered that the three parts of anucleotide are found in equal proportions- Sugar- Phosphate- Nitrogen Base12
Discovering the Structure of DNAErwin Chargaff, 1951- Austrian-American biochemist- Analyzed base composition of DNAfrom various species and observedregular relationships:- Adenine Guanine Thymine Cytosine- A T and C G13
Discovering the Structure of DNARosalind Franklin and Maurice Wilkins, 1952- English scientists- Used a technique called X-ray diffraction- It took Franklin 100 hours to obtain “photo51”14
Discovering the Structure of DNAFranklin reasoned that the DNA is a helixwith symmetrically organized subunitsFigure 9.415
Discovering the Structure of DNAJames Watson and Francis Crick- Did not perform any experiments- Used results of othersand cardboard cutouts tobuild a model of thestructure of DNAFigure 9.516
DNA StructureA single building block is a nucleotideEach nucleotide is composed of:- A deoxyribose sugar- A phosphate group- A nitrogenous base; one of four types- Adenine (A), Guanine (G) Purines- Cytosine (C), Thymine (T) Pyrimidines17
DNA StructureFigure 9.7Figure 9.618
19
DNA StructureNucleotides join via abond between the5’-phosphate of oneand the 3’ hydroxylof another- This creates acontinuous sugarphosphatebackboneFigure 9.820
Polarity and antiparallel nature ofthe two DNAstrands (5’ and3’ ends)21
Two polynucleotide chains align forming adouble helix- The opposing orientation (head-to-toe) iscalled antiparallelismFigure 9.922
One strand of thedouble-helix runs ina 5’ to 3’ direction,and the otherstrand runs in a 3’to 5’ directionFigure 9.1123
DNA StructureThe key to the constant width of the double helix is thespecific pairing of its complementary bases viahydrogen bonds24
DNA is Highly CondensedThe DNA coils around proteins called histones,forming a bead-on-a-string-like structureThe bead part is called the nucleosomeThe nucleosome in turn winds tighter formingchromatinChromatin fibers attach in loops to scaffold proteinshttp://www.biostudio.com/demo freeman dna coiling.htm25
Figure 9.1326
Molecular Definition of a GeneA gene is a segment of DNA that directsthe formation of RNA to produce proteinThe protein (or functional RNA) createsthe phenotypeInformation is conveyed by the sequenceof the nucleotides27
DNA ReplicationAt first, researchers suggested that DNAmight replicate in any of 3 possible waysModel of DNAReplication1. Conservative2. Semiconservative3. DispersiveOrganization of DNAStrandold/old new/newold/new new/oldmixed old & new28
DNA ReplicationMatthew Meselson and Franklin Stahl, 1957- Grew E. coli on media containing 15N forseveral generationsDNA with 15N is heavy- Moved bacteria to media containing 14N- Then traced replicating DNA- Determined that DNA replication is semiconservative29
Meselson-Stahl ExperimentFigure 9.14Figure 9.1430
Overview of DNA ReplicationDNA replication occurs during the S phaseof the cell cycle, prior to cell divisionHuman DNA replicates about 50 bases/secA human chromosome replicatessimultaneously at hundred points along itslengthA site where DNA is locally opened is calleda replication fork31
Overview of DNA ReplicationFigure 9.1532
Enzymes in DNA ReplicationFigure 9.1633
Activities at the Replication Fork34
Activities at the Replication Fork35
Activities at the Replication Fork36
Activities at the Replication Fork37
Fidelity of DNA replication & maintaining DNAintegrityMaintained by:1. Proof-reading function of DNA polymerase2. DNA repair smatch repair-lg.movDNA damage and repair in generalhttp://www.youtube.com/watch?v y16w-CGAa0Y&feature relatedhttp://www.youtube.com/watch?v nPS2jBq1k4838
Genetic Integrity and DiversityNeed for maintaining genetic integrity is balancedby having enough genetic variability for naturalselection to act onFew errors of DNA replication are not corrected!39
1 DNA Structure & Replication (Outline) Historical perspective (DNA as the genetic material): Genetic transformation DNA as the transforming agent DNA is the genetic material in bacterial viruses (phage) Historical perspective (Structure of DNA): Identifying ribose and deoxy ribose
DNA Structure and Replication 3 Model 2 - DNA Replication Direction of DNA helicase DNA helicase Free Nucleotides 11. Examine Model 2. Number the steps below in order to describe the replication of DNA in a cell. _ Hydrogen bonds between nucleotides form. _ Hydrogen bonds between nucleotides break. _ Strands of DNA separate.
DNA replication DNA replication occurs at distinct cis-acting elements of DNA. Such origins of replication are used to nucleate the duplication of the genome. Two replication forks are generated at each origin and DNA replication occurs in a semi-conservative manner
Genetic transformation and DNA DNA is the genetic material in bacterial viruses (phage) The base-pairing rule DNA structure. 2. Basis for polarity of SS DNA and anti-parallel complementary strands of DNA 3. DNA replication models 4. Mechanism of DNA replication: steps and molecular machinery
DNA Replication 1. Explain semi-conservative replication. Prior to cell division, a cell must make a copy of its DNA to pass along to the next generation. Copying DNA is called “replication”. Rather than build a DNA molecule from scratch, the new DNA is composed of one old DNA strand (used as the template) and one brand new strand.
DNA Replication What are the key events of the template model for DNA replication? –helicase unwinds the double helix –the two exposed strands of DNA act as a template for DNA replication –DNA polymerase adds th
DNA replication begins at a specific site called origins of replication. A eukaryotic chromosome may have hundreds or even a few thousand replication origins. Proteins that start DNA replication attach to the DNA and separate the two strands, creating a replication bubble. At each end of the replication
control DNA replication in C. elegans, as well as their functions in particular stages of development and specific cell types. Several techniques used for analysis of DNA replication in C. elegans are summarized in BOX 1. 3. The factors that regulate DNA replication The regulation of DNA replication in
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