Molecular Genetics Chapter 4

Self-Study Read sections 4.1 and 4.2 on your own. You will be responsible for knowing a few of the experiments, which led to the discovery of location of Hereditary Material and DNA Structure. Suggested Questions: Pg. 216 #1-6 and 10.

Example – summarize each experiment and significance Key PlayersExperiment and Discovered GriffithUsed mice with different strains of pneumococcus (virulent and non-virulent). Observed that when heat treated virulent, mixed with non-virulent was injected into healthy mouse it died. Discovered process of transformation (meaning something in the diseased bacteria even when heat treated acts on the healthy bacteria) HammerlingObserved regeneration of alga “cap” but not “foot” when foot cut off. Nucleus contained in the foot, meaning that hereditary info is stored in the nucleus ChargaffDiscovered that in DNA the number of A=T and G=C Hershey & Chase Used radioactive labelled viruses(bacteriophages) to infect bacteria cells seeing if protein or DNA passed along hereditary information. Concluded it was DNA that was injected into the bacteria cell and thus the genetic material necessary to make new viruses. FranklinUsed Xray crystallography that suggested a double helix (also noted the accurate diameter of the DNA molecule) Watson & Crick Deduced the structure of DNA using the information from Chargaff, Franklin and Wilkins

4.3 DNA Replication and Repair

How does DNA replicate? Meselson and Stahl determined a Semiconservative Model Means that a replicated DNA molecule is composed of one parent strand and one newly synthesized strand Experiment used radioactively labeled DNA from E.coli

DNA Replication III

Leading and Lagging Strands 5’ 3’ 5’ 3’ Direction of unwinding Leading Strand 5’ 3’ RNA Primer 5’ 3’ Primer 5’ 3’ Lagging Strand Reads template 3’  5’ Builds new strand 5’  3’

Enzymes Acting During New DNA Strand Synthesis: DNA Helicase – unzipping DNA Gyrase – reduce tension of unwinding SSB’s – help keep strands apart DNA Polymerase III – adds nucleotides to create new strand (complimentary base pairing) DNA Primase – lays down RNA primer (“temporary” 6-10bp) Acting After Elongation of New DNA Strand: DNA Polymerase I – replaces RNA primer and proofreading DNA Ligase – joins gaps between okazaki fragments

How It Happens DNA helicase Reads template 3’  5’

Mechanism for Incorporating New Nucleotides DNA Polymerase III adds free Dioxyribonucleoside triphosphate (dNTP) Always added to the 3’-OH end (since new strand builds in 5”  3’ direction) Bond breaks between first two phosphates to drive process of elongating the strand (2p recycled to make more dNTP) 3 Phosphates Deoxyribose

Mechanism for Incorporating New Nucleotides

Key Points to Know: Each parent strand acts as a template (semiconservative model) Reads DNA template 3’  5’ and Builds 5’  3’ Mechanism for joining dNTP’s Know which is your Leading strand (towards fork) and Lagging strand (away from fork) Know all acting enzymes and proofreading process

Try Some Questions Pg. 223 Q# 1,2,5 Pg. 230 Q# 4,6,7 Handout – will help quiz and review steps “Awareness Presentation” (due Dec19th) More realistic animation of DNA replication