Chapter 16 Section 1 – Pt. 1 Pgs. 305 – 310 Objective: I can describe how scientists deduced that DNA is the source of genetic material through well designed experiments.

 Mendel: unit of hereditary information that determines a character…(called…)  Gene  Genes found in (from big to small…)  Nucleus  Chromosomes  DNA (what genes are made out of)  We didn’t know this before. We’ll look at experiments that PROVE this in order to better learn how to think scientifically  allow you to make future discoveries!

 Spanish Influenza Bacteria (streptococcus pneumoniae)  S strain – has capsule – mice died  R strain (mutant) – no capsule – mice lived

 Tried to determine if capsule causes death  Heat killed S strain – still has capsule – mice lived

 Mixed heat-killed S strain (made harmless) with living R strain (already harmless)  Mice died  When examine dead mice, found:  Heat-killed S strain  Living S strain, too!  Live with capsule!  Asserted that R transformed into S  Something carried over

 Repeated Griffith experiment to find what caused transformation:  What contained “gene” to make capsule (which was transferred from heat-killed S to living R in order to transform it)  At the time people believed genes on chromosomes (events of meiosis matched Mendel’s Laws – Segregation, Indep. Assr.)  Chromosomes made of 2 macromolecules  Nucleic Acid  DNA  Proteins  Histones, Scaffold Proteins

 Took heat-killed S strain  Removed 99.98% of all protein  Repeated experiment (mix heat-killed S w/ living R)  Found transformation STILL occurred  So, protein did NOT contain “gene”  Noted a “transforming principle”  Same chemistry, behavior as DNA  Not affected by lipid, protein, or RNA extraction/digestive enzymes  WAS affected by DNA-digesting enzymes

Scientists still skeptical – why?

 Worked with viruses that infect bacteria  A.K.A. Bacteriophage (phage = virus)  Virus attach to bacteria and insert genes  Viral genes take over normal cell genes  Tells cell to only produce viruses  Cell is dying  Cell bursts (dies) releasing (spreading) new viruses

 Bacteriophage has simple structure (2 parts) 1) Protein coat – protect DNA 2) DNA – instructions (genes) to make more virus  Debate over which carries genes  Virus is so simple, no doubts about interfering variables  Answer?  How discover?

 Used radioactive isotopes to label parts  Protein coat labeled with 35 S  DNA labled with 32 P  Can later detect where radiation is

 Two groups: 1 w/ protein labeled 1 w/ DNA labeled  Allow infection  Shake tubes to dislodge viruses  Centrifuge to isolate cells  Detect where radiation is found why? ation.com/olcweb/cgi/pl uginpop.cgi?it=swf::535 ::535::/sites/dl/free/ /120076/bio21. swf::Hershey+and+Cha se+Experiment (in cell or out cell) (bottom or top of tube) V I

 Rosalind Franklin – X-ray diffraction  James Watson and Francis Crick  Put it all together