Molecular Genetics

History of DNA

Discovery of DNA

• Friedrich Miescher (late 1860s)- collected used bandages at hospitals and

immersed in salt solution (to release cells)- alkaline solution caused lysis of cells and

nuclei to precipitate out- isolated substance with high P content in

the nuclei, called it “nuclein”- http://www.dnaftb.org/dnaftb/15/concept/

Frederick Griffiths (1920s)(Image from: http://www.thefullwiki.org/Griffiths_experiment)

Joachim Hämmerling (1930s)(Image from: http://www.seavegetables.com/handbook/genera/greens/Acetabularia/Acetabularia.htm)

• experiments with single-celled alga called Acetabularia

• determined that the nucleus is the organelle that contains hereditary information

Hämmerling Expts (1930s)(Image from: http://www.accessexcellence.org/RC/VL/GG/hammerling_s.php)

Hämmerling Expts (1930s)(Image from: http://www.biologie.uni-hamburg.de/b-online/e14/9.htm)

DNA or protein?(Image from: http://textbookofbacteriology.net/phage.html)

• Alfred Hershey & Martha Chase (1952)

• experiments with virus: bacteriophage T2

• bacteriophage infects bacteria cells by attaching itself and injecting its DNA into the cell

DNA or protein?

• Bacteriophage cells infecting bacteria cells:

DNA or protein?

• Alfred Hershey & Martha Chase (1952)- proteins contain sulfur but not phosphorus- DNA contains phosphorus but not sulfur- Hershey & Chase tagged viral proteins with radioisotope 35S and viral DNA with radioisotope 32P- after infection by labelled bacteriophages, bacteria cells were isolated from protein coats of viruses

DNA or protein?

• Alfred Hershey & Martha Chase (1952)- bacteria cells contained 32P but no 35S- culture medium (containing viral protein coats) contained 35S

DNA or protein?

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html

Molecular Genetics

Structure of DNA

Composition of DNA

• Erwin Chargaff (1949)- isolated DNA from different organisms and measured levels of each of the 4 nitrogenous bases

- amts of adenine = amts of thymine

- amts of cytosine = amounts of guanine

Rosalind Franklin (1953)(Image from: http://www.stanford.edu/group/ccr/blog/2009/04/a_closer_look_1.html)

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

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

Structure of DNA

• James Watson & Francis Crick (1953)-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 for deducing the structure of DNA

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

Structure of DNA

• James Watson & Francis Crick (1953)

Structure of DNA

4.2

See also 1.2 (pages 52-54)

Nucleic Acids(Image from: http://giangleblog.wordpress.com/2011/05/02/edit-5-dna-structure-group-b/)

• polymers of nucleotides:

• 5 carbon sugar (ribose or deoxy-)

• nitrogenous base C1

• phosphate group C5

RNA vs DNA(Image from: http://www.biology.lsu.edu/introbio/summer/Summer2004/1201/RF/Chapter%205%20review.htm)

RNA vs DNA(Image from: http://dedunn.edublogs.org/2011/06/08/structure-of-dna-and-rna/)

DNA & RNA Directionality(Image from: http://www.phschool.com/science/biology_place/biocoach/transcription/chains.html)