7 - Biol 241 - 2010 Lecture 13: DNA structure I) Genetic...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Biol 241 - 2010 Lecture 13: DNA structure I) Genetic materials need to have 4 major characteristics 1) replication 2) storage of information 3) expression of information 4) variation by mutations Before 1944, proteins were thought to be the genetic materials. At the time, DNA was thought to exist as tetranucleotide repeats (put forth by Levene). Thus DNA structure appeared to be too simple for code for information. Careful analysis of E. Chargaff showed that this tetranucleotide hypothesis was incorrect. Instead Chargaff estaablished two rules regarding the nucleotide content: 1) in any organism, G=C and A=T, and 2) the ratios of nucleotides vary from one organism to next. II) Evidence that DNA is the genetic material 1) Transformation (Oswald Avery, Colin MacLeod, and Maclyn McCarty, 1944): A) In 1927, Frederick Griffith described two strains of Diplococcus pneumoniae , one virulent (infectious) and one avirulent (noninfectious). The difference in virulence is caused by the polysachharide capsule fo the bacterium. The virulent and the nonvirulent strains were also designated S (smooth) and R (rough) respectively, based on the colony morphology when plated on agar. B) Injection of living type III S (virulent) kills mice. Injection of living type II R (avirulent) does not kill mice. Injection of heat-killed type III S also does not kill mice. Griffith’s critical experiment was to co-inject type II R (avirulent) with heat-killed type III S into mice. Surprisingly, mice dies and type III S (virulent) bacteria were found. Griffith concluded that heat-killed type III S bacteria transformed live avirulent type II R cells into virulent type III S one. He called the agent for the event the transforming principle . C) In 1931, Henry Dawson showed that this could occur in vitro, thus mouse
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/09/2010 for the course BIOL 241 taught by Professor Henrychang during the Spring '10 term at Purdue University-West Lafayette.

Page1 / 3

7 - Biol 241 - 2010 Lecture 13: DNA structure I) Genetic...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online