Ch. 16: The Molecular Basis of Inheritance …the nature of DNA

Evidence that DNA is the genetic material Griffith’s Experiment Streptococcus pneumoniae Molecules has the ability to change phenotype of various cells. (bacteria) = Transformation

Griffith’s Experiment

… more evidence that DNA is the genetic material Evidence that Viral DNA can program cells Hershey-Chase Experiment T4 phage and E.coli Either protein coat OR DNA will infect cell Tagged coat and DNA with radioactive markers Showed that the nucleic acid inside virus is transmitted to host cell

Hershey-Chase Experiment

DNA Structure DNA is a Double Helix - like a twisted rubber ladder made from three main components (like legos) Sides of the ladder are composed of alternating sugar and phosphate pieces Each “rung” of the ladder is made up of two complementary bases A bound to T C bound to G DNA is put together in chunks called NUCLEOTIDES Each nucleotide has a sugar, PO43- and base

Purines and Pyrimidines Nucleotide Purine

DNA Structure Double Helix Chargaff: Rosalind Franklin Watson/Crick %G = %C Rosalind Franklin X Ray Chromatography Shape Width Spacing b/w nucleotides Watson/Crick Built Model of DNA using info above Determined bonding of A-T and G-C

DNA Replication Possibilities

Replication #1 DNA Helicase comes on the scene UNWINDS the DNA UNZIPS the DNA This site is known as the replication bubble

Replication #2 Complementary Bases begin adding into both sides of the ds DNA Needs DNA Polymerase Enzyme A binds with T, C binds with G (no other possibility because of the shape of the bases!) The DNA Polymerase precedes the paired bases and clips out any that are already added ahead of it (on the 3’ end) with an exonuclease activity

Replication #3 Finally you have 2 identical copies of ds DNA The final job of the Polymerase is to Proofread the NTP’s after they are added (back on the 5’ end) and to clip out any that are incorrectly paired DNA Ligase fuses backbone of DNA

DNA Replication and Repair Base pairing, semiconservative Necessary enzymes Helicases DNA polymerases DNA ligase Make new DNA in a 5´3´ direction Needs a Primer for DNA Polymerase to attach to DNA Proof-reading and repair of damage mismatch repair excision repair

Priming DNA Synthesis

Two Strands of DNA are AntiParallel Sugar phosphate backbone run in opposite direction. Each strand has a 3’ and 5’ end New strand of DNA can ONLY be made in 5’  3’direction OR Follows old DNA in 3’  5’ direction Leading strand Lagging Strand

Lagging Edge also forms from 5’ to 3’. Forms Okazaki Fragments. Leading Edge of DNA Replication New strand forms 5’ to 3’ continuously Lagging Edge also forms from 5’ to 3’. Forms Okazaki Fragments. DNA Replication Review

Difficulty in ends of DNA

Difficulty in ends of DNA Telomeres: Section of nucleotide sequence containing no genes Telomerase: enzyme that catalyzes lengthening of DNA May have factors in determining life span May be related to cancer

Telomeres/Telomerases