Molecular Genetics

Structure of DNA

Phoebus Levene (1920’s)

• identified the 3 components of DNA molecule– deoxyribose sugars– phosphate groups– nitrogenous bases

• 4 nitrogenous bases identified by 1949

Erwin Chargaff (1949)

• isolated DNA from different organisms and measured levels of each of the 4 nitrogenous bases

• amt. of adenine = amt. of thymine• amt. of cytosine = amt. of guanine

Rosalind Franklin

• produced X-ray diffraction images of DNA that suggested its double helix shape

• diameter 2nm, one turn 3.4nm

• See animation: http://www.dnalc.org/view/15014-Franklin-s-X-ray-diffraction-explanation-of-X-ray-pattern-.html

James Watson & Francis Crick (1952)

• used information from Chargaff and Franklin’s work

• proposed a model of DNA with a double helix of 2 anti-parallel strands

• won the Nobel Prize in 1962 (with Maurice Wilkins) for deducing the structure of DNA

http://www.dnaftb.org/dnaftb/19/concept/index.html

Structure of DNA

Review of 1.5 p.45-46

Nucleic Acids

• polymers of nucleotides:

• 5 carbon sugar (ribose or deoxy-)

• nitrogenous base C1

• phosphate group C5

RNA vs DNA

RNA vs DNA

DNA & RNA Directionality