BIOL 1441 1st Edition Lecture 28 Outline of Last Lecture I Inheritance of sex linked genes II Color blindness III Barr Body IV Genetic disorders Outline of Current Lecture I DNA II Transformation III DNA replication model Current Lecture I DNA Deoxyribonucleic Acid a 1953 James Watson Francis Crick introduced double helix structure of DNA b Hereditary information encoded in DNA c Whole code every single cell of the body d DNA directs its own replication e DNA is the genetic material f Early in the 20th century the identification of the molecules of inheritance loomed as a major challenge to biologists g Morgan s group showed genes located on chromosomes 2 components of chromosomes DNA protein candidates for the genetic material 1910 h Search for the Genetic Material i Protein great heterogeneity and specificity of function requirements for hereditary material ii Little known about DNA too uniform to account for multitude of specific inherited traits i Frederick Griffith 1928 i Worked with 2 strains of the bacteria Streptococcus pneumoniae These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II 1 Rough R strain harmless 2 Smooth S strain pathogenic ii Why does smooth coat cause infection 1 Encapsulated immune cells can t detect it Transformation a Change in genotype and phenotype due to uptake of foreign DNA b Griffith doesn t solve the question i Provides a clue c Something in that smooth bacteria was inserted into the live rough bacteria transforming them into smooth bacteria d A genetic trait was passed from one organism to another e Find the material responsible for transformation find the hereditary molecule f How does R transform to S i Protease transformation ii DNase no transformation iii DNA is responsible for transforming ability NOT protein g Bacteriophages i Phages viruses that only infect bacteria highly specific ii Hershey Chase 1953 1 Use T2 phage infects E coli 2 Viruses DNA protein iii Viruses infect bacteria hijack host replication machinery to make virus proteins instead of host proteins 1 Viral coat stays outside bacteria protein iv What do the viruses inject into the bacteria to replicate themselves 1 DNA or protein v Experimental Design 1 Grow T2 phage in radioactive sulfur 35S a Labels proteins only no sulfur in DNA 2 Grow T2 phage in radioactive phosphorus 32P a Labels DNA only 3 Infect separate samples of E coli vi Results 1 Labeled protein all in supernatant a Pellet contained bacterial cells no labeled protein 2 Labeled DNA all in pellet with bacteria 3 Shows that DNA is transferred into bacterial cell not protein 4 DNA must be the molecule responsible for replicating transferring genetic information h Erwin Chargaff 1947 i DNA composition varies from one species to the next 1 Molecular diversity from one species to next ii Chargaff s Rule III 1 If you run an experiment and find a species of bacteria has 33 adenines what percentage of guanine does this species have a 33 adenine 33 thymine b 66 total DNA c 100 66 34 DNA d 34 DNA 17 guanine 17 cytosine i DNA is Genetic Material how does it replicate itself i Already known that DNA is a polymer of nucleotides 1 Nitrogenous base 2 Sugar 3 Phosphate group 4 Structure Function ii Want to know how DNA confers heritability figure out the structure j X Ray Diffraction i X rays diffract as pass through purified fibers of DNA producing spots and smudges ii Use mathematical equations to translate patterns into information about the 3D shapes of the molecules iii Wilkins behind Franklin s back shows Watson the famous photograph 51 iv Photo 51 enabled Watson to deduce that DNA was helical figure the width of the helix the spacing of the nitrogenous bases v The width suggested that the DNA molecule was made up of two strands forming a double helix vi Watson Crick built models of a double helix to conform to the X rays chemistry of DNA vii Franklin had concluded that there were 2 antiparallel sugar phosphate backbones with the nitrogenous bases paired in the molecule s interior k Genetic Diversity i Base pairing dictates the combinations of nitrogenous bases the sequence of nucleotides along each strand is not restricted ii Linear sequence could be varied in countless ways iii Each gene has a unique order or base sequence l Watson Crick Wilkins received the Nobel Prize in medicine or physiology for their determination of the structure of DNA m Franklin died in 1958 of ovarian cancer she was only 37 yrs old n Nobel Prize can be awarded only to the living Franklin could not be honored Replication Model a Relationship between structure and function is manifest in the double helix b Watson Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material c The Basic Principle Base Pairing to a Template Strand i 2 strands of DNA are complementary each strand acts as a template for building a new strand in replication ii In DNA replication the parent molecule unwinds and two new daughter strands are built based on base pairing rules