Photo 51Ellie Morlino Period 10/11 chem.

Rosalind

Franklin

and the

structure

of DNA

Photo 51 • Taken by Rosalind Franklin in 1952

Rosalind Franklin• 1920- 1958

• She obtained her PhD at only 26

• She began working in x-ray diffraction -- using x-rays to create images of crystalized solids.

•  She adjusted her equipment to get an extremely fine beam of x-rays. She extracted finer DNA fibers than ever before and arranged them in parallel bundles. Her research allowed her to discover crucial keys to DNA's structure.

Photo 51 is an x-ray diffraction image of DNA (x-ray crystallography)

It was Critical evidence in identifying the structure of DNA

Significance

X+ 6y(5(8x)y)

-65

The “X”

• The law of diffraction states that X- rays moving through a helical shape diffract at angles perpendicular to the helix

• This creates the X shaped diffraction pattern (outlined in blue)

The Four Diamonds• These diamond shapes are

formed by the arms and legs of the X

• This shows that the pattern of the helix repeats above and below the central X shape, which indicated the continuation of the helix.

• The completely white diamonds on the top and bottom versus the darker diamonds of the left and right show that DNA’s sugar- phosphate backbones are outside of the molecule, and the bases are inside the molecule.

X-Ray Crystallography0  It is used to determine the

arrangement of atoms within a crystalline molecule.

Steps to take a picture using Xray Crystallography

0 1) An adequate crystal must be obtained

0 2) A beam of X-rays is shined through it, and depending on the angles and intensities of the scattered beams, a crystallographer can create a three dimensional picture of the electron

density of the crystal.

0 3) From the electron density information, the mean positions of the atoms within a crystal can be

determined, and the structure of the molecule can be determined

Structure of DNA0 Made up of four different parts

called nucleotides0 Each nucleotide consists of a sugar

(deoxyribose) bound on one side to a phosphate group and bound on the other side to a nitrogenous base

0 The four bases in DNA are:0 adenine (A) - a purine(double-

ringed)0 cytosine(C) - a pyrimidine(single

ringed)0 guanine (G) - a purine0 thymine (T) - a pyrimidine

Chemical reactions happen in DNA too!

0 DNA Replication-process that occurs in all living organisms and copies their DNA therefore maintaining it’s structure

1. Replication fork is formed2. Helicase Enzyme unwinds Double

Helix into two strands 3. New strands are synthesized4. The leading strand is synthesized5. The four strands pair up and wind

back together creating two new Double Helixes

Steps

DNA Replication Chemical Equation:

(DNA)n + dNTP ↔ (DNA)n+1 + PPi (Deoxynucleoside triphosphate)

( pyrophosphate)

Since this equation goes both ways, either side could be the reactant or product of the other, depending on the situation.

Photograph 51 Production0There is a play called

Photograph 51 by Anna Ziegler

o shows Rosalind’s role in discovering the structure of DNA

Sources

0 http://www.pbs.org/wgbh/aso/databank/entries/bofran.html

0 http://www.seattlerep.org/Plays/1213/PH/Synopsis

0 http://www.ruppweb.org/xray/101index.html