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The Nobel Prize and Pond Scum as a Model Organism

By Jeffrey Norris, UCSF Science Cafe | October 16, 2009

A man is a man and a mouse is a mouse, but if you talk to a few biomedical scientists about their research, at least one is likely to spring the term "mouse model" on you.

But there actually are many so-called model organisms. They are used as stand-ins to learn more about what most of us are really interested in - ourselves, our health, our afflictions and how our bodies work. Cost, convenience and how accurately a critter can model particular biological processes shared with humans play a role in the choice of organism employed. The mouse often comes out on top.

But UCSF's Elizabeth Blackburn, PhD, will receive a share of this year's Nobel Prize for Physiology or Medicine for studies she began in the 1970s on a model organism that has just one cell. When Blackburn began the prize-winning work, she was looking to solve a puzzle about DNA and cell division that that was so fundamental, it pertained to protozoans as well as people.

Blackburn sought to discover how cells can overcome a biochemical step during cell division that results in a shortening of the ends of DNA molecules each time a cell replicates its genetic material.

Without something to protect the DNA, one would think that humans would be unable to develop normally, and that protozoans would go extinct as successive generations lost another bit of the genetic blueprint.

It turns out that the DNA in each chromosome has expendable, protective DNA capping it, so that gene-encoding DNA is not lost during cell division. Blackburn was the first to describe this DNA, called a telomere. Later in her own lab, Blackburn worked with Carol Greider, then a graduate student, to identify an enzyme called telomerase, which can lengthen and replenish telomeres in each chromosome within the cell. Telomere length and telomerase now are known to play a part in cancer and in other human diseases.

But why did Blackburn start with Tetrahymena, a single-celled protozoan she often refers to as "pond scum"? Why not study human cells or cells or creature more similar to us?

Read more at Jeffrey Norris, UCSF Science Cafe