The DNA Race

Is Heredity Protein or DNA? Scientists understood that chromosomes are the means of heredity. But chromosomes contain equal parts DNA and Protein. Which part is the gene?

Griffith and His Mice 1928 – Fredrick Griffith paved way for others to point out that DNA was composed of genes. Studied mice & 2 strains of bacteria (caused pneumonia) R (rough) strain & S (smooth) strain

Conclusion to Griffith R  mouse = lived. S  mouse = died S (Killed) = lived S (Killed) + R = died WHY? S strain “Transformed” R strain. S-strain has “Inheritance Molecule”

Transformation The process during which bacteria are changed by absorbing genetic material from an outside source

But, what material is actually being transformed or transferred? Is it the protein or the DNA?

Hershey & Chase Settled DNA/protein debate 1952

Bacteriophage (virus)

What does DNA look like?

Erwin Chargaff Chargaff’s Rule Early 1950’s

Erwin Chargaff 1940 – Noticed pattern in amounts of bases A,G,C,&T found in DNA. Source of DNA: A T G C Strept Yeast Herring Human Strept Yeast Herring Human

Chargaff’s Rule Adenine & Thymine Guanine & Cytosine

Franklin & Wilkins X-ray of DNA molecule 1951

Rosalind Franklin & Maurice Wilkins Crystallized DNA molecule  X-ray pattern. Got first picture of DNA Twisted coils (like a spring) 2 strands in the structure

Franklin & Helix Picture

Watson & Crick Solved mystery of DNA structure 1954

Watson & Crick 1953 – Tried to make model of DNA. Saw Franklin’s picture and were able to do it. Double Helix Model Rungs of Ladder = Bases (Chargaff’s Rule) Sides of Ladder = Sugar + Phosphate.

Watson & Crick Model