The History of DNA TSW explain how the genetic code is contained within DNA TSW investigate the exploration of DNA structure

What is DNA? DNA stands for Deoxyribonucleic Acid DNA is present in the nucleus of all eukaryotic cells DNA controls all the chemical changes which take place in cells The kind of cell which is formed (i.e. muscle, blood, nerve, etc) is controlled by DNA The kind of organism which is produced (i.e. buttercup, giraffe, herring, human, etc) is controlled by DNA

DNA Molecule DNA is a macromolecule (i.e. “Giant Molecule”) made up of a long chain of sub-units (monomers) called NUCLEOTIDES Each NUCLEOTIDE has 3 main parts… Phosphate Group (SUN) 5-Carbon Sugar (HOUSE) Nitrogenous Base (POOL)

Nucleotide Structure In DNA, the phosphate, DEOXYRIBOSE sugar, and a nitrogenous base combine to form a NUCLEOTIDE adenine deoxyribose PO4

DNA’s Structure DNA is a double helix (*think twisted ladder) 4 Nitrogenous Bases Adenine Thymine Guanine Cytosine

Nitrogenous Bases Purines Pyrimidines Adenine (A) Guanine (G) A or G Thymine (T) Cytosine (C) A or G T or C

More DNA Structure Sugar-Phosphate backbone (sides of the ladder) Nucleotides held together by H bonds (rungs of the ladder)

Discovering DNA: A Team Effort Frederick Griffith (1928) Question: How do bacteria make people sick? Answer: Transformation

Transformation Process in which one strain of bacteria is changed by a gene(s) from another strain of bacteria

Oswald Avery (1944) Question: Which molecule is important for transformation? Answer: DNA stores & transmits genetic info from 1 generation to the next

Hershey & Chase (1952) Question: Are genes made of DNA or protein? Experiment: Which part of a bacteriophage enters the bacterium? Answer: DNA

Hershey/Chase Experiment

Erwin Chargaff DNA base-pairing rules Adenine must pair with Thymine Guanine must pair with Cytosine Their amounts in a given DNA molecule will be about the same.

What does base-pairing look like? C G H-bonds T A

Chargaff’s Rule Remember: Bases form the rungs on the “DNA ladder” by complementary pairing

“Race for the Double-Helix” Rosalind Franklin (1952): Used X-ray to determine that DNA is spiral-shaped Watson & Crick (1953): Created 1st accurate model of DNA (double-helix), won the Nobel Prize

Draw the complementary strands CAGGCCTAC CATTGCAAG TAAGCGATA GCCATGAAT *Don’t forget Chargaff’s Rule