Standards 5b. Know how to apply base- pairing rules to explain precise copying of DNA during semi- conservative replication

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”

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 1950s – 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

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.

Structure of DNA Composed of NUCLEOTIDES Sugar Phosphate group Nitrogen base

Nitrogen Bases Purines: A= adenine G= guanine Pyrimidines: T= thymine C= cytosine

Structure of DNA Which bases pair together? A with ____ G with ____

Basic structure of DNA * Double Helix: two chains of nucleotides * Sugar and phosphate groups make up backbone * Nitrogen bases on opposite strands are attracted to each other * A – T and G – C