Rosalind Franklin and X-ray Diffraction

Rosalind Franklin• Born in July 25, 1920 in

London, England• Died April 16,1958 in

London, England (ovarian cancer)

• Attended and excelled at an all girl’s school in London (the school taught chemistry and physics)

• Graduated in 1941from Newman College, Cambridge

• 1942 worked at British Coal Utilization Association (studying carbon and graphite microstructures)

• 1945 earned Ph.D. in physical chemistry from Cambridge University

• 1947-1950 worked in Paris where she learned X-ray diffraction techniques

Accomplishments

Accomplishments

• 1951-returned to London to work in John Randall’s laboratory at King’s College, London as a research assistant

• 1951-1953 came close to solving the DNA structure

• Moved to J. D. Bernal’s Lab at Birkbeck College and worked on tobacco mosaic virus and the polio virus

X-ray diffraction

• Definition– The scattering of x-rays by crystal atoms that

produces a pattern that yields information about the structure of the crystal. The wavelengths of x-rays are comparable in size to the distances between atoms in most crystals. X-ray diffraction is the basis of x-ray crystallography

http://science.education.nih.gov/supplements/nih4/technologyother/glossary.htm

• X-ray diffraction is used to be able to determine the structural information about crystalline structures– Can be used on complex biomolecules to

determine their 3-D shapes

• Used in:– Solid-state physics– Biophysics– Medical physics– Chemistry– biochemistry

A Brief History of X-ray diffraction

• 1895—first discovered by Roentgen• 1914—first diffraction pattern made of a crystal• 1915—theory proposed to determine crystal

structures from diffraction patterns• 1953—Watson and Crick propose the DNA

structure with the aid of photo 51 from Rosalind Franklin

• Current—through use of computer aided technology, atomic structures are being determined as well as uses in medical applications

How diffraction works• Diffraction can be used on various materials

including a single particle, solids, and crystalline materials.– Single particles

• Incident beams scatter uniformly

– Solids• beams scatter and interfere constructively in some

patterns. This will produce diffracted beams• Random arrangements of material will cause beams

to randomly interfere and will not produce a distinctive pattern

How diffraction works (cont’d)

– Crystalline materials• Regular patterns of crystalline materials produce

distinct diffraction patterns• The type of patterns produced gives information

about the crystal structure of the material

http://www.matter.org.uk/diffraction/introduction/what_is_diffraction.htm

http://search.aol.com/aol/imageDetails?invocationType=imageDetails&query=x-ray+diffraction&img=http%3A%2F%2Fwww.chem.missouri.edu%2Fx-ray%2Fimages%2Fbigmolecule.jpg&site=&host=http%3A%2F%2Fwww.chem.missouri.edu%2Fx-ray%2F&width=99&height=123&thumbUrl=http%3A%2F%2Fimages-partners-tbn.google.com%2Fimages%3Fq%3Dtbn%3A79DKhJNpTqr5lM%3Awww.chem.missouri.edu%2Fx-ray%2Fimages%2Fbigmolecule.jpg&b=image%3Fquery%3Dx-ray%2520diffraction

X-ray diffraction diagram

http://mrsec.wisc.edu/edetc/modules/xray/X-raystm.pdf

Analyzing patterns

• Data is complied from all angles

• There are recognizable patterns for simple crystal structures

• Diffraction patterns taken from each angle can be complied to produce a 3-D electron density map

The scientists behind the discovery of the DNA structure

• Several scientists were involved– Rosalind Franklin: physical chemist and

expert in x-ray crystallography• Was the first person to crystallize and

photographed B-DNA • Famous Photo 51

http://www.pbs.org/wgbh/nova/photo51/pict-01.html#fea_top

• Maurice Wilkins– Peer and collaborator of Rosalind Franklin

• James Watson and Francis Crick– Chemists– Used information from Rosalind Franklin’s

Photo 51 and molecular modeling to solve the structure of DNA in 1953

Analysis of Photo 51• Showed the now famous “X”

pattern of the helical shape• The diamond shapes in the

photo indicate long, extended molecules

• The spacing in the photograph is smeared which indicates distances between repeating structures

• In the photograph there appears to be missing smears. This indicates an interference from the second helix structure

Analysis of Photo 51• Showed the now famous “X”

pattern of the helical shape• The diamond shapes in the

photo indicate long, extended molecules

• The spacing in the photograph is smeared which indicates distances between repeating structures

• In the photograph there appears to be missing smears. This indicates an interference from the second helix structure

www.pbs.org/wgbh/nova/photo51

Analysis of Photo 51• Showed the now famous “X”

pattern of the helical shape• The diamond shapes in the

photo indicate long, extended molecules

• The spacing in the photograph is smeared which indicates distances between repeating structures

• In the photograph there appears to be missing smears. This indicates an interference from the second helix structure

www.pbs.org/wgbh/nova/photo51

Analysis of Photo 51• Showed the now famous “X”

pattern of the helical shape• The diamond shapes in the

photo indicate long, extended molecules

• The spacing in the photograph is smeared which indicates distances between repeating structures

• In the photograph there appears to be missing smears. This indicates an interference from the second helix structure

Analysis of Photo 51• Showed the now famous “X”

pattern of the helical shape• The diamond shapes in the

photo indicate long, extended molecules

• The spacing in the photograph is smeared which indicates distances between repeating structures

• In the photograph there appears to be missing smears. This indicates an interference from the second helix structure

The secrets of Photo 51• After analysis of Photo 51, the

following information was obtained:– The structure was a double

helix– The radius of the structure is

10 angstroms– The distance between nitrogen

bases is 3.4 angstroms– The distance between each

turn of the helix is 34 angstroms

Secrets of Photo 51• The use of Photo 51 along with other

discoveries lead to the following:– DNA was made up of a sugar, a phosphate

group and 4 nitrogenous bases (adenine <A>, thymine <T>, cytosine <C>, and guanine <G>)

– Chargaff’s Rule applies here:• The same amounts of adenine and thymine are

found in DNA

• The same amounts of cytosine and guanine are found in DNA

• %A=%T

• %C=%G

Modeling DNA

• James Watson and Francis Crick modeling DNA structure

http://www.chemheritage.org/classroom/chemach/pharmaceuticals/watson-crick.html

References (n.d.). X-Ray Diffraction Message posted to

http://www.pbs.org/wgbh/nova/photo51/

(n.d.). Rosalind Elsie Franklin Message posted to http://www.sdsc.edu/ScienceWomen/franklin.html (

n.d.). What is X-Ray Diffraction Message posted to http://www.bioinformatics.nl/webportal/background/xray...

(n.d.). X-Ray DIffraction Message posted to http://science.education.nih.gov/supplements/nih4/tech... (

n.d.). X-Ray Diffraction-FInding the Structure of DNA Message posted to http://www.branta.connectfree.co.uk/x-ray_diffraction.htm

Ardell, D. (2006, Oct. 25). Rosalind Franklin (1920-1958) Message posted to http://www.accessexcellence.org/RC/AB/BC/Rosalind_Fran...

Day, E. & Ross, S. (2004). X-Ray Diffraction Message posted to http://www.nhn.ou.edu/~johnson/Education/Juniorlab/Pre... Diffraction