History of DNA

In 1928, the British scientist was studying the way in which certain types of bacteria cause the disease pneumonia When Griffith injected the mice with the disease-causing strain of bacteria, the mice developed pneumonia and died When the mice were injected with the harmless strain they did not get pneumonia & did not die When the mice were injected with a mixture of both harmless and heat-killed bacteria (from the disease-causing strain) they developed pneumonia & died Griffith ’ s final conclusion is that one strain of bacteria had been transformed into another – They called this process transformation FREDERICK GRIFFITH 1928

Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth) Heat-killed, disease- causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumoniaLives Live, disease-causing bacteria (smooth colonies) Dies of pneumonia GRIFFITH’S EXPERIMENT

– CONCLUSION: Transformation – somehow, the heat-killed disease-causing bacteria transferred its disease- causing ability to the harmless bacteria FREDERICK GRIFFITH 1928

Repeated Griffith ’ s work in 1944 to see if they could discover which molecules were the transforming factor. Avery and his colleagues made an extract, or juice, from the heat-killed bacteria They treated the extract with enzymes that destroy lipids, proteins, and carbohydrates, but they discovered that transformation still occurred When they treated the nucleic acids (DNA) with enzymes, the transformation did not occur This means that DNA is the transforming factor that carries the genetic code AVERY, MCCARTY, MACLEOD 1944

– CONCLUSION: DNA was the transforming factor AVERY, MCCARTY, MACLEOD 1944

Studied viruses that infect bacteria (1952) – bacteriophages Wanted to learn whether the protein coat, DNA, or both parts from the virus enter the bacterium Made two batches of the virus and labeled each with a radioactive isotope – By adding the radioactive isotopes to the viruses, they were labeling the virus ’ protein and DNA Protein – sulfur 35 DNA – phosphorous 32 HERSHEY & CHASE 1952

They mixed the radioactive viruses with the bacteria, and then separated the mixture by placing it in a centrifuge Results showed that DNA enters the bacteria, but the protein coat stays outside This experiment showed conclusively that DNA carried the genetic code HERSHEY & CHASE 1952

ROSALIND FRANKLIN & MAURICE WILKINS 1950’s In the 1950 ’ s, used X-ray evidence to help discover the structure of the DNA molecule To do this, she purified large amounts of DNA and stretched the fibers in a thin glass tube so the strands were parallel Next she aimed a narrow X-ray beam on the DNA and recorded the pattern on film Her results gave two important clues about the shape of DNA – Twisted shape – Groups of molecules spaced at regular intervals Maurice Wilkins was Franklin ’ s assistant and is a shared recipient of the Nobel Prize

ROSALIND FRANKLIN Women in Science: A Controversy It was Franklin's photograph of the DNA molecule that sparked a scientific revolution. Wilkins showed Watson the photo, and, Watson said, "My jaw fell open and my pulse began to race." The photo showed, for the first time, the essential structure of DNA -- the double-helix shape, which also indicated its method of replication.

Observed that in any sample of DNA, the number of adenine molecules was equal to the number of thymine molecules – Same was true for guanine and cytosine Provided one of the key steps in developing a structure model of the DNA molecule Source mol % of bases Ratios %GC A G C T A/T G/C PhiX ¦ Maize * Octopus Chicken Rat Human ERWIN CHARGOFF 1950’s

FRANCIS CRICK & JAMES WATSON 1953 Using Franklin ’ s and Wilkins ’ ideas, Watson & Crick developed a model showing the strands of DNA were twisted around each other to form a double helix Their model explains another characteristic about DNA structure – The nitrogenous bases on each of the strands of DNA are positioned exactly opposite each other – Used Chargoff ’ s ideas of how bases bond together and called it base pairing

FRANCIS CRICK & JAMES WATSON 1953 Presented their model in 1953 and along with Maurice Wilkins, won the Nobel Prize – Why wasn ’ t Rosalind Franklin recognized for her accomplishments? She died in 1958 and only living scientists can win

CURRENT AREAS OF RESEARCH HUMAN GENOME PROJECT Website Nucleotide base sequencing for all our 30,000+ human genes What trait, what gene, what chromosome(s), what it does

FORENSIC SCIENCE – DNA FINGERPRINTING Chemically isolate DNA, cut it into pieces, sort it by size, denature it by heating or chemically treating, & finally blot it by fractionation and bake it onto paper What about a world-wide DNA database? What are some potential issues? Benefits? CURRENT AREAS OF RESEARCH

DNA TESTING FOR BIODIVERSITY, EVOLUTIONARY TRENDS, & ANIMAL BEHAVIOR Needed for genetic variation within/among populations Mating and reproductive strategies Obtaining gene pools is essential when designing programs for management of wildlife species CURRENT AREAS OF RESEARCH

STEM CELL RESEARCH Embryonic stem cell controversy – George Bush, early 2000’s George Bush, early 2000’s Use of somatic stem cells – Reverse engineering Reverse engineering CURRENT AREAS OF RESEARCH