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Winemaker’s Bookshelf By Gary Strachan Aha! moment at the molecular level


Contents of Nessa Carey’s short book on epigenetics can take a long time to grasp.


I


've been reading an interesting book lately, The Epigenetics Revolution, by Nessa Carey. ISBN 978-1-84831-315-6 (ePub) or 978-184831-292-0 (print). It's only a short book, 188 pages, but it was a slow read because I had to keep rereading parts of it to grasp the material.


Carey has done a masterful job of tracing the development of molecular genetics. She gets her points across by using examples as familiar as the biography of Audrey Hepburn, a Harry Potter movie, and the genetics of tortoise shell cats. The fascinating part of epigenetics is that we can now relate many familiar phenomena to their underlying molecular events.


My formal courses in genetics ended in the mid 1970s. The “Central Dogma” of Watson and Crick was state of the art knowledge. All of the codes which define the processes of life are contained within DNA templates deep within each cell. These codes are transcribed onto short lengths of RNA, which are fed into a small machine, the ribosome. The messages on messenger RNA (mRNA) are translated into amino acid sequences, which become the functional proteins of living cells. When we developed rapid methods for DNA analysis it became clear there was far too much DNA in the average cell to account for the number of proteins in a functioning plant or animal. There were long repetitive sequences that didn't seem to do anything except take up space. They were dubbed “junk DNA,” because nobody knew why they were there.


The Central Dogma offers no explanation of the control of DNA expression that results in production of the various cell types and tissues of a functioning organism. Each cell


British Columbia FRUIT GROWER • Fall 2014 21


type contains the same DNA but the expression of that DNA differs. What controls the


development of a leaf instead of a root of a plant? How does a plant initiate flowers at a certain point in its life cycle?


The modification of DNA expression in organisms without affecting the fundamental inherited DNA passed from parent to offspring is the science of


epigenetics. In a complex organism with millions of cells, this produces cells of different tissues such as roots, leaves, and fruit in a plant, all coded from identical DNA but selectively expressed. The


fundamental biochemical control of epigenetic expression is almost identical throughout the whole range from yeast to complex organisms


such as plants or people. This is where junk DN takes over. It's common knowledge that all life


forms on earth store their genetic information in various sequences of the four DNA bases: adenine (A), thymine (T), guanine (G), and cytosine (C) and that these sequences are the templates to manufacture cellular proteins. Enzymes made of protein are the workhorses of life. They facilitate all the chemical reactions that enable plants and animals to develop and operate. Less known is that the protein structures (mostly enzymes) for all organisms are closely related. The amino acid sequences of the


functioning proteins are almost identical to proteins of yeast, plants and animals.


It is intuitive that enzymes with the same function would be common between different species but is


there any relatedness between the thousands of enzymes required for a single-celled organism and the millions of enzymes of complex


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