1. 4.2

2.  It was determined that DNA comprises of three main components: deoxyribose sugar, phosphate group (-), nitrigenous base.  These three components make up a ________________. These are held together by _______________ bonds (between the ____________ and ___________ groups.

3. Erwin Chargaff (1949)  Proportion of adenine = proportion of _______________  Proportion of guanine= proportion of _______________  Proportion of pyrimidines = proportion of __________ Structure of Nucleotides  Nitrogenous base attached to 1’ carbon of the sugar by a glycosyl bond.  Phosphate group attached to the 5’ carbon by an ester bond.

5.  Carries hereditary information  Controls cellular processes  Accommodates for individual variation  Replicates itself

6.  What was known:  Chemical composition of DNA (not structure!)  Relative proportions of nitrogenous bases to each other.  What was the structure?  Linus Pauling: California  Rosalind Franklin & Maurice Wilkins: London  Using X-ray diffraction analysis/ X-ray crystallography  Molecule bombarded with X-rays  X-rays deflected by atoms  pattern of lighter and darker lines on photographic film.  Math used to decipher the 3-D shape.  James Watson & Francis Crick: Cambridge U.  Wilkins presented them with informal look at Franklin’s diffraction pattern before it was published (boo!)  Revealed that DNA has the shape of a helix about 2 nm in diameter, with a complete helical turn every 3.4 nm.  Used Franklin’s info + Chargoff’s results to build the famous model of the double-helix structure of DNA in 1953.  Wilkins, Watson, and Crick awarded the Nobel Prize in 1962.

7.  Born to liberal-minded parents  she was raised in the same manner as her brothers.  At 15, she decided to pursue a career in science, despite the lack of female role models in the scientific community in the 1930s.  Did extensive research with X-ray chrystallography.  Died of cancer at the age of 37 in 1958, working until the very end in her wheelchair.  She may have been awarded the Nobel Prize had she been alive.

9.  Consists of two antiparallel strands of _______.  Bases of one strand paired with bases in the other strand facing inward towards each other.  Purine is always paired with a pyrimidine: complimentary base-pairing.  Which scientist led to this idea?  If sequence of one strand is known, the sequence of the complimentary strand is known.

10.  Yeah, so?  This is consistent with the base-pairing rules  If two purines bond together: wider at some points.  If two pyrimidines bond together, less than 2nm.  Complimentary base pairs held together by hydrogen bonds  Individual H-bond weak  ‘strength in numbers’: DNA is stable.

11.  One strand runs in the 5’ to 3’ direction.  One strand runs in the 3’ to 5’ direction.  3’ end:  Terminates with the hydroxyl group of the deoxyribose sugar  5’ end:  Terminates with a phosphate group.  By convention, only the 5’ – 3’ strand written when indicating the sequence of nucleotides. Why? _______________________

13.  Page 216, #1-3, 5-10.