DNA Replication

Nucleotides

T.H. MorganGenes are located on chromosomes

Transformation (Griffith 1928)

Avery, McCarty, MacLeod (1944)

Genetic MaterialProtein or DNA ????

"Studies on the chemical nature of the substance inducing transformation of pneumococcal types"

Phages

Hershey & Chase (1952)

Linus Pauling (1948)Alpha Helix Structure

Chargaff’s RuleAdenine – ThymineGuanine - Cytosine

Watson & Crick

Maurice WilkinsX-ray diffraction

Rosalind Franklin

Nucleotides

X-ray Data

DNA Structure

Complimentary Strands

Semiconservative Model

(Meselson & Stahl)

Semiconservative Model(Meselson & Stahl)

Origin of Replication

DNA Nucleosides Triphosphates

Antiparallel

EnzymesDNA PolymeraseHelicaseSingle-strand binding proteinTopoisomeraseRNA primaseLigase

RNA PrimerUses RNA primase to build RNA primerEventually replaced with DNA by DNA Polymerase

DNA Replication

Leading and Lagging StrandsLeading Strand

Built in the 5’-3’ directionBuilt toward the replication forkBuilt continuouslyUses one RNA Primer

Lagging StrandBuilt in the 5’-3’ directionBuilt away from the replication forkBuilt discontinuously using Okazaki fragmentsMany RNA Primers

Overview

ProofreadingMismatch RepairNucleotide Excision Repair (nucleases)

End-replication ProblemNucleotides can only be added to 3’ end

Leaves gap on leading strand

Each replication causes DNA molecule to get smaller

Telomeres

TelomeresEnd of DNA strand made up of reoccurring DNA sequenceCan be rebuilt with telomerase (only in germ-line cells)