Presentation on theme: "Chapter 16 The Molecular Basis of Inheritance. Question? Traits are inherited on chromosomes, but what in the chromosomes is the genetic material? Two."— Presentation transcript:
Chapter 16 The Molecular Basis of Inheritance
Question? Traits are inherited on chromosomes, but what in the chromosomes is the genetic material? Two possibilities: Protein DNA
Qualifications Protein: very complex. high specificity of function. DNA: simple. not much known about it (early 1900’s).
For testing: Name(s) of experimenters Outline of the experiment Result of the experiment and the importance of the result
Griffith - 1928 Pneumonia in mice. Two strains: S - pathogenic R - harmless
Result Something turned the R cells into S cells. Transformation - the assimilation of external genetic material by a cell.
Problem Griffith used heat. Heat denatures proteins. So could proteins be the genetic material? DNA - heat stable. Griffith’s results contrary to accepted views.
Avery, McCarty and MacLeod - 1944 Repeated Griffith’s experiments, but added specific fractions of S cells. Result - only DNA transformed R cells into S cells. Result - not believed.
Hershey & Chase -1952 Genetic information of a virus or phage. Phage - virus that attacks bacteria and reprograms host to produce more viruses.
Bacteria with Phages
Phage Components Two main chemicals: Protein DNA Which material is transferred to the host?
Used Tracers Protein - CHONS, can trace with 35 S. DNA - CHONP, can trace with 32 P.
Experiment Used phages labeled with one tracer or the other and looked to see which tracer entered the bacteria cells.
Result DNA enters the host cell, but the protein did not. Therefore: DNA is the genetic material.
Chargaff - 1947 Studied the chemical composition of DNA. Found that the nucleotides were in certain ratios.
Chargaff’s Rule A = T G = C Example: in humans, A = 30.9% T = 29.4% G = 19.9% C = 19.8%
Why? Not known until Watson and Crick worked out the structure of DNA.
Watson and Crick - 1953 Used X-ray crystallography data (from Rosalind Franklin) Used model building. Result - Double Helix Model of DNA structure. (One page paper, 1953).
Book & Movies “The Double Helix” by James Watson- His account of the discovery of the shape of DNA Movie – The Double Helix