October Update

Bought a standard poodle puppy.  Bringing him home October 5, so October will be full of housebreaking, and FUN.

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WONDER OF THE MOMENT

Entries in protein (2)

Tuesday
Sep072010

RNA Miracles: First Genetic Molecule! Who Knew?  

Every new biological discovery opens the door to a world of undreamed of miracles.

         Back when Rosalind Franklin elucidated the structure of DNA and Francis Crick and James Watson figured out how DNA genes might work, no one really knew much about RNA.  Gradually researchers discovered that a molecule christened “messenger RNA” (mRNA) transcribed genes from DNA.  Two other types of RNA then translated the mRNA into proteins. 

         And what was the purpose of these proteins?  In plants, animals, fungi, and various single-celled organisms, some proteins form rigid or moving structures, some provide storage or transport, some fight off infection, and some proteins catalyze the myriad chemical reactions that keep cells alive and doing their jobs.

         So genes turned out to build organisms and run them by this method: DNA makes RNA, and RNA makes protein.

         But this was just the tip of the iceberg.

         For instance, when DNA makes RNA, and RNA makes protein, each step of this process is engineered by proteins (enzymes).  Yet each protein was translated from genes (DNA).  And the genes got transcribed and translated by RNA.  So biologists began thinking that these molecules and this process couldn’t have sprouted from nothing.  Something had to come first.  Was it the DNA?  The RNA?  The protein? 

         Whatever came first had to have two functions.  It had to be able to store the plans for each living organism—genes do this.  And it had to be able to catalyze biochemical reactions in cells—enzymes do this.

         At last, Nobel Prize winners Thomas R Cech and Sidney Altman came upon RNA enzymes that could do both the job of a gene and the job of an enzyme.  Such a molecule was dubbed a “ribozyme.”  Ribozymes may well be the ancestors of both DNA and enzymes made of protein.  After the first ribozymes made it possible for successful cells, or perhaps mere successful molecules, to be duplicated, how might DNA and proteins have come about?

         Even today, there are RNA viruses whose RNA gets “back-copied” into DNA.  Perhaps the first DNA came about in such a way.  And even today many ribozymes join with proteins to modify their catalytic activity.  Perhaps the first protein enzymes came about in such a way.  It’s exciting to imagine such molecular evolutions happening billions of years ago.

         But RNA turns out to have many talents: More on this in my next post.

´╗┐

Thursday
Jul192007

What we didn't expect from the Human Genome Project

The history of DNA research is a tale of patient researchers laboring day after day on myriad tiny problems.  It is a tale of myriad answers leading at last to profound insights.

    This is what happened with the Human Genome Project.  The question the HGP set out to answer was:

• What are all the genes in a human being?

    Before the Project began, geneticists had learned a lot.  They knew that genes work by manufacturing proteins.  They knew that genes do this indirectly:  Enzymes in the cell nucleus unroll and unzip the DNA double helix and copy a target gene into messenger RNA.  The messenger RNA carries the gene’s code to cell parts outside the nucleus to direct protein manufacture.  Finally, geneticists knew that humans have around 100,000 proteins in their bodies.  So researchers expected the HGP to take years and to turn up about 100,000 genes.

    But the geneticists working on the Project, devised new, speedier techniques for decoding DNA.  A lot sooner than anticipated, the whole human genome was known.  And there weren’t 100,000 genes—there were only about 30,000!  Or maybe only 25,000!  A humbling conundrum.

• How do the 100,000 proteins come from only 25,000 genes?

    Before the Human Genome Project, something else had come to light:  When a messenger RNA gets copied from one of our genes, it gets “edited.”  Molecules called spliceosomes cut the RNA message into fragments, remove some of the fragments, and splice the rest back together again.  The spliced message is what actually gets translated into a protein.  But the spliced message isn’t always the same.  The set of fragments that get spliced together can differ.  So that alternative proteins result from the same messenger RNA and therefore from the same gene!

    Is this how 25,000 genes make 100,000 proteins?  How did this incredible system evolve?   Some biologists think the first active catalytic molecules of life were RNA, while others think they were protein.  Intriguingly, spliceosomes have some of both.  Could alternative splicing be connected to the earliest molecules of life?  When we investigate this editing of RNA, are we seeing far back into life’s beginnings, just as we see far back into the beginnings of the universe when we investigate the oldest light we can find with the Hubble Telescope?