MadSci Network: Molecular Biology

Re: How can I preserve my DNA?

Date: Thu Jan 4 17:27:00 2001
Posted By: Amanda Kahn, Grad student, neuroscience, UCSF
Area of science: Molecular Biology
ID: 977084821.Mb

Hi Dean!

Forgive my asking, but aren't you a little young to be worried about the 
future of your nucleic acids?  

You are correct that our DNA suffers cumulative and irreversible damage over 
time.  For instance, the telomeres which form the "ends" of each linear, 
double-helical human chromosome get smaller with each cell division.  Some 
models of aging have suggested that telomere shortening acts as an intrinsic 
clock for cells; after a certain number of divisions, the cells die.  
Exposure to environmental factors, including UV light or free radicals, can 
also alter DNA.

Getting DNA out of cells isn't too difficult.  Basically, you need to lyse 
the cells, remove the carbohydrates/lipids/proteins/RNA, and isolate the 
remaining DNA.  You can extract bacterial DNA by lysing the cells in an 
alkaline-detergent solution, then using centrifugation and various solvents 
to get rid of proteins.  RNA is removed by treating with RNase enzymes.  For 
mammalian cells, the problem is a little trickier -- the chromosomes are 
long, so you want to treat the DNA gently to avoid shearing.  Many biotech/
chemical companies sell kits which make it easy to extract pure, unscathed 
human DNA, or you can use the simple techniques referenced below.

Here's the rub: while in principle you only need a few cells to get 
sufficient DNA for certain molecular biology techniques, in practice it 
takes a lot of cells to get a visible speck of DNA.  For bacteria, you can 
grow oodles of cells in just 1 mL of medium, so that's not a problem.  For 
human cells, blood (maybe 10 mL or so) is the preferred source.  A GP should 
be able to draw blood in her office quickly and (more or less) painlessly, 
using appropriate techniques.  Only a subset of the cells contained in blood 
will be useful for your purposes, since red blood cells do not contain 
nuclei.  Centrifugation is the preferred method of separating white cells 
from the rest of the blood.

I would not advise any invasive surgical procedures to acquire stem cells 
and the like -- really, you need not have your GP mining for bone marrow or 
liver.  If you're afraid of needles, I suppose you could scrape epithelial 
cells from the inside of your cheek and culture them, but contamination with 
all the nasty bacteria that live inside our mouths would be a potential 

As for storage, DNA stores well in a buffered solution (like TRIS-EDTA) at 
-20 C (a standard freezer temperature).  No liquid nitrogen necessary.

Here's a smorgasbord of DNA extraction tips (how to extract DNA from human 
cells, bacteria, lice, and so forth ....):

Hope this helps, and have fun!
Amanda Kahn

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