EPIGENETIC APOCALYPSE NOW: I warned you.

This is going to be so boring that I will insert the picture LAST, and put you on your honor to read all the way to the bottom before you look at it.

Things you may already know:

                DNA consists of an enormously long sequence of four “bases”,  abbreviated A,C,T, & G.  These are types of organic molecules (nucleic acids) and are very similar, but with important differences.

                A sequence of three bases, called a “codon”, will “code for” an amino acid.  These things we call proteins are nothing more than long strings of amino acids, which naturally assume some characteristic shape.  The shape depends on the sequence and the chemical and electrical properties of the amino acids.
                Proteins are the workhorses of the body.  They can only do their jobs if they have the right shape.

                To make a protein from a DNA blueprint the sequence must first be “transcribed” onto a DNA-like molecule called a messenger RNA (mRNA).  Once transcribed the information is transported to a copying machine (ribosome) and “translated” into a chain of amino acids, which then folds and scrunches to make a protein.  Making a protein from a DNA sequence is called “expressing” it.

                All cells have the complete DNA sequence, but in specialized cell only a few are “expressed”.  You do not, for instance, grow hair in your teeth – although in your dissolute youth you may at times have thought you had.

Things you may not know:

                There are things called “promoters” that initiate “transcription” of a sequence of bases (a gene).  If the promoter is screwed up, the gene doesn’t get expressed properly, or at all.

                mRNA  frequently is modified after being transcribed by things called micro RNAs (miRNA),as well as by other proteins.  miRNAs are  a relatively new discovery, and I predict they will play a large role in cancer research.

                Sometimes the protein coming newly hatched from the ribosome also is modified before going to work.

I must say, the entire process strikes me as so blindingly and unnecessarily complicated that, in a way, it proves natural selection; natural selection by environmental conditions acting on completely random deviations..  It provides good  evidence against Intelligent Design;  if “designed”, the process   resembles a Rube Goldberg contraption slapped together  by a Designer with a peculiar sense of humor.

NOW, some things I think I know and partially understand that I would like to share with you:

                “Epigenetic” means “on top of, in addition to” – stuff like that” –genetics.  It is a science which treats of the ways that gene expression is regulated.  The reason that you do not grow hair in your teeth is because the genes for hair growth are blocked(in your teeth) by things called “epigenetic markers”. 

                An epigenetic marker can consist of something (a molecule) attached to the DNA strand.  Often this is a “methyl” group (one carbon atom attached to three hydrogens and carrying a positive charge.)  If a methyl group gloms onto the promoter for a gene (a specific length of DNA) it may stop that gene from being expressed.  Apparently patterns of methylation can be inherited, and after studying Nessa Carey’s book I even know how – but I know you don’t care, so I will spare you.  Another way that epigenetic markers modify gene expression is called “histone acetylation.”  This calls for more biology – but hang in there, I’m almost done.

Histones are proteins.  They form little knots (“octomers”, called “nucleosomes”) around which the DNA strand can be tightly wound.  Winding is essential; cells are so small you can’t see them, but a typical strand of DNA is six ft. long!  Clearly, to transcribe a stretch of DNA into RNA the knot has to be partially unwound.  The ability of a nucleosome to be unwound can be affected by a process called “acetylation”, which is the addition of an acetyl group to the histone proteins.  (For you would-be chemists and any other masochists, an acetyl group is CH₃CO-).  Apparently acetylation is not inherited.

There are many other kinds of epigenetic markers; Wikipedia will give you an entire paragraph-full of them.  But these are enough.

So why have I put you through all of this (you didn’t just skim, did you?)?  I did it because many novel cancer-fighting methods are based on epigenetics.  Say you have a gene that, when mutated, serves as an oncogene and stimulates cell division.  How to silence it?  Methylation!  Or, acetylate the hell out of the nearby nucleosomes, prevent  unwinding and thus transcription – ergo, no active oncogene.  They are hard at work on epigenetic drugs, and if they succeed they will deserve their BMWs, in my view.

I won’t do this to you again.  I promise.  Well, maybe once or twice more.  You know me; I never lie!

               

Linda and Patches, awake

If there is a cuter picture anywhere, I've yet to see it