DNA Structure

How it was discovered

Friedrich Miescher 1869 (Germany)

• Isolated deoxyribonucleic acid from nucleus of cells– Called this white,

slightly acidic chemical “nuclein”

– Didn’t know it was genetic material

Frederick Griffith 1928 (England)• Working on vaccine for pneumonia bacteria• Discovered that by killing inside of bacteria, it

wouldn’t give disease to mice

Many Scientists 1940

• By this time, many scientists isolated all of the chemicals found in DNA– Phosphate (PO4)

– Sugar (deoxyribose)– Four nitrogen bases (adenine, thymine,

cytosine, guanine)• Now called “deoxyribose nucleic acid”

or DNA

Oswald Avery 1944 (USA)

• Worked with bacteria that causes pneumonia

• Used DNA-destroying enzyme to kill DNA inside bacteria before inserting it into animal– Animal didn’t get

pneumonia– DNA is genetic material

Structure

• … was still unknown– How did the phosphate, deoxyribose, and

4 bases fit together?• Knew that amount of adenine ALWAYS

equaled amount of thymine• Knew that amount of cytosine

ALWAYS equaled amount of guanine

Rosalind Franklin 1951 (England)

• Worked on x-ray crystal diffraction photographs (how light bounced off crystals) of DNA structure

• Worked in same area as Maurice Wilkins who tended to treat her as his assistant– Wilkins was working on separate

DNA projects

James Watson and Francis Crick, 1953 (England)

• Wilkins showed Watson Franklin’s x-ray photograph

• Watson said "The instant I saw the picture, my mouth fell open and my pulse began to race.”

– Showed photo to Crick who instantly began work with Watson on DNA model using balls and sticks• 1953 scientific paper

published called “A Structure for Deoxyribose Nucleic Acid’

Nobel Prize 1962

• Maurice WilkinsMaurice Wilkins,, Francis CrickFrancis Crick, and James WatsonJames Watson received Nobel Prizes for Physiology or Medicine for work on DNA structure– Rosalind Franklin was not honored– She died 4 yrs earlier in 1958 at age 37 of ovarian

cancer