MadSci Network: Genetics
Query:

Re: If DNA can not be seen then how do scientists know for sure that it exsist

Date: Mon Mar 20 14:51:42 2000
Posted By: Christine Broussard, Post-doc/Fellow, Genetic Disease Research Branch, National Human Genome Research Inst.
Area of science: Genetics
ID: 951754936.Ge
Message:

Hi Danielle,
	While it is true that we cannot see DNA with the naked eye, there are 
many techniques that can be used to visualize DNA.  Electron microscopes can 
be used to look at DNA on a large scale, i.e. the entire molecule.  Chemical 
techniques allow the precipitation of DNA into viscous solutions readily 
seen by the naked eye.  In addition, there are dyes which can bind to the 
DNA and glow when light of a particular wavelength shines on it.
	X-ray crystallography is a technique which solves the structures of 
molecules mathematically based on a pattern of diffraction generated when x-
rays hit a crystal.  The molecule of interest has to be "grown" as very 
small crystals (which can look like quartz under the microscope).  X-rays 
are passed through the crystal and a pattern of diffraction (bending of the 
rays) is generated on film.  Particular structures bend x-rays in different 
ways.  Thus one can identify which structures are present in a particular 
molecule.
	The first person to discover the structure of DNA was a scientist named 
Rosalyn Franklin.  She used X-ray crystallography to learn more about the 
structure of DNA.  A double helix (the normal DNA structure) gives a 
particular pattern of diffraction.  Unfortunately, she died at age 38, 
before the Nobel Prize was given for this discovery.  Though she was never 
recognized for this important discovery, other scientists working on the 
structure of DNA at the same time used her data to solve the double helix.



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