Transcript Discovering DNA: Structure and Replication
Discovering the Structure of DNA
What is DNA?
• • • DNA = deoxyribonucleic acid Stores, transmits and copy all information Located in the cell’s nucleus
What do you know about DNA?
• • • • Codes for proteins nucleic acid Monomer is a nucleotide The three parts of a nucleotide: – – 1. Phosphate group 2. Sugar (deoxyribose) – 3. Nitrogen base
Nitrogen bases • nitrogen two types: purine- 2 carbon rings pyrimidine . -1 carbon ring
More about nitrogen bases • DNA has 4 nitrogen bases: – Thymine (T) – Adenine (A) – Cytosine (C) – Guanine (G) • • A G - purines C T - pyrimidines.
YouTube: DNA Structure of DNA
A collaborative effort!
• • • • Early 1900s – – known: information is passed from cell to cell. Unknown: what carried the information?
scientists thought a protein others that it was a nucleic acid.
Three major experiments helped shows nucleic acid carried cell information: – – – Griffith Avery Hershey-Chase
Frederick Griffith • • • • studied pneumonia bacteria 1928 isolated two strains of pneumonia injected them into mice
– Griffith got lucky?
Something transferred from heat-killed bacteria
–
What happened?
• •
Griffith’s conclusions:
Transformation bacteria = process by which one strain of bacteria changes the gene(s) of another
Avery • • • • • DNA was transforming bacteria 1943 Uses pneumonia ( just like Griffith) Showed gene is made of DNA Scientists were slow to accept the results
Hershey and Chase • bacteriophages to see if information is carried on proteins or DNA • 1950 • Further supported Avery’s experiment that genetic material is DNA http://www.accessexcellence.org/RC/VL/GG/images/HERSHEY.gif
Discovery of the structure of DNA • Many scientists contributed to determining the structure of DNA – Erwin Chargaff – – Rosalind Franklin James Watson & Francis Crick
Erwin Chargaff • • • • • Base pairing rule 1950 percentages of bases in DNA 10% A = 10% T 40% C = 40% G • This is Chargaff’s Rule!
Rosalind Franklin • • • • x-ray photography to try to find DNA structure 1952 Her “Photo 51” revealed DNA’s structure Died of cancer in 1958
Watson and Crick • http://teachers.sduhsd.k12.ca.us/lolson/im ages/watson_crickjpg Credited with finding the structure of DNA) • 1953 • Watson got a sneak peak at Franklin’s x-ray photos and used them with other evidence • Did not give credit to Franklin
DNA structure • • • • Twisted ladder made of nucleotides Sides- phosphate/sugar Rung- nitrogen bases
What bonds with what?
– – A bonds with T G bonds with C – Bonds sides- covalent- strong rungs - hydrogen - weak
• Your turn...the structure of DNA On the diagram: – Circle and label a nucleotide.
– – – – – Label the sugar and phosphate molecules.
Label the bases Label a base pair.
Label the sugar phosphate backbones.
Label the hydrogen bonds.
Sugar /P backbone Base pair A Hydrogen bonds A A G G C T T C Sugar /P backbone P S G nucleotide