The Feb. 17 issue of Current Biology1 has a Q&A magazine feature on the genetic code. After dismissing some myths about it being universal, consisting of only 20 amino acids and obligated to only three codons (there are some minor exceptions to these mostly-true principles: see 04/30/2003), the authors tackle the big question: where did it come from?I heard about a ‘frozen accident’�One of the first proposals, in 1968, for the origin of the code, was Francis Crick’s ‘frozen accident’ model. But the discovery of alternative codes showed that the code is not frozen. And similar codons are assigned to similar amino acids, indicating that the code is not an accident.So, how did the code evolve?There are several theories that try to explain the origin of the code. Most can be classified in one of three major groups.Chemical: posits that direct chemical interactions between amino acids and their cognate codons/anticodons influenced codon assignment. Studies of binding of RNA aptamers to amino acids showed that, for at least some amino acids – arginine, tyrosine and isoleucine – such chemical interactions do exist. These theories fail to explain the assignment of codons that do not show direct interactions to their cognate amino acids.Historical: proposes that an initially smaller code grew by incorporation of new amino acids. For example, new amino acids may have captured codons from their metabolic precursors, contributing to the assignment of similar amino acids to similar codons.Selection: suggests that the code was selected to minimize the phenotypic effects of point mutations. The code’s organization supports this: nonsynonymous substitutions often lead to replacement of an amino acid by one chemically similar, causing little disruption in the protein.Accumulating evidence for these models suggests that they are not mutually exclusive. Rather, the code probably evolved by an interplay among some or all of them. Direct interactions of short RNA molecules and amino acids may have fixed the assignment of certain codons, while subsequent assignments may have been driven by history and selection.(Emphasis in original.)1Andre R.O. Cavalcanti and Laura F. Landweber, “Magazine: Genetic Code,” Current Biology Vol 14, R147, 17 February 2004.They just violated Occam’s razor. They also violated the rule that three wrongs don’t make a right. The “Chemical” theory is the old biological predestination idea that Dean Kenyon abandoned. If RNA happens to bind to three amino acids better than the 17 others, that does not explain how they subsequently linked via peptide bonds to form a polypeptide with any catalytic activity. Amino acids do not have the ability to link up by themselves. Getting just one element of the complex protein machinery that can translate DNA and construct a protein is astronomically improbable, to put it mildly (see our online book).The “Historical” theory is hysterical, because it personifies amino acids. One cannot ascribe purposeful processes to chemicals. No cheating with natural selection, either; it cannot even begin to a player unless an accurate system of self-replication is already working.The “Selection” Theory also personifies the chemicals: the code was selected to minimize … point mutations” Enough of this passive-voice nonsense. Who selected it, and why would he/she/it want to, if not to optimize the system? The sentence makes perfect sense in intelligent design theory, but is bizarre otherwise. No cheating with natural selection here, either. The authors committed one more foul: card stacking. All their theories assume naturalistic evolution. They left out the only theory that explains the observations without violating Occam’s razor: intelligent design. (Visited 41 times, 1 visits today)FacebookTwitterPinterestSave分享0
Share Facebook Twitter Google + LinkedIn Pinterest Brrrrrr!I consider myself a fairly cold tolerant person. I spend my early winters outside for many hours a day in the Christmas tree fields in all kinds of weather. I grow facial hair. I wear flannel, stocking caps and coveralls. I cut many cords of firewood and I really do truly enjoy winter, snow and cold weather. I handled (and even enjoyed) winter’s worst this season, but these chilly March winds and damp conditions made me yearn for warmer spring days ahead.It seems as March wears on each year, I am ready for spring to arrive just a little sooner. My daughter and I were discussing the continually unpleasant weather in early March. I passed along some sage wisdom from my youth: “They always used to say if March came in like a lion it would go out like a lamb.” But after multiple appearances of the early March lion, my daughter and I are still eagerly waiting on the late March lamb.I know we are not the only ones ready for spring. Enduring a seemingly endless March is longstanding Midwestern tradition. Here are some other March weather insights from year’s gone by from the Farmers’ Almanac to take note of as we head into spring:• A dry March and a wet May? Fill barns and bays with corn and hay.• As it rains in March, so it rains in June.• March winds and April showers? Bring forth May flowers.• So many mists in March you see, so many frosts in May will be.• Is’t on St. Joseph’s day (19th) clear,So follows a fertile year;Is’t on St. Mary’s (25th) bright and clear,Fertile is said to be the year.In a recent podcast, Joel Penhorwood shared the “The 11 seasons of Midwestern states” that he’d found online that may be more accurate for the Ohio weather we have been seeing in recent years. Here are the 11 seasons one can expect in Ohio: Winter, Fool’s Spring, Second Winter, Spring of Deception, Third Winter, Mud Season, Actual Spring, Summer, False Fall, Second Summer (1 week), and Actual Fall.In the estimation of our podcast group consisting of myself, Dale Minyo, Ty Higgins and Joel, we had Fool’s Spring back in February, which was followed by a fairly definitive Second Winter through early March. The wonderful sunshine and temperatures in the 50s for the Spring of Deception took place the last couple days of the Ohio Beef Expo and the day after (and to me this also always seems to coincide with some of the best of March Madness basketball watching). As I write this, temperatures have plummeted back into the 30s and there is a miserable mix of freezing rain and a bone-chilling breeze for a truly awful Third Winter, setting us up for yet another Mud Season.Looking forward, Jim Noel with National Oceanic and Atmospheric Administration National Weather Service Ohio River Forecast Center is predicting the coming weeks to be influenced by La Niña.“La Niña, cooling of the eastern equatorial Pacific Ocean waters, remains in place and is classified as a weak La Niña. This means many other things will ultimately impact our weather and climate since it is weak, but it will contribute to our pattern. Indications are this could linger into spring and possibly summer before ending. Regardless of when it ends, it tends to impact weather patterns in the atmosphere longer, sometimes up to three to six months later. So there will be a contribution to our climate pattern into at least the planting season if not growing season,” Noel said in the OSU Extension CORN Newsletter. “December to February will go down as slightly warmer and wetter than normal. Even though we had really cold periods in there, the very warm second half of February wiped all the winter cold away. Snowfall will go down in many areas as not too far from normal, a bit above or below depending on where you live. The main snow message was the snow kept coming and going away during winter.”The cooler weather of March looks like it will spill over into April.“The outlook for April calls for cooler and wetter than normal conditions with the last freeze normal or slightly later than normal. Expect 4-inch soil temperatures to track normal or slightly behind schedule,” Noel said. “After a slightly cooler and wetter spring (delayed planting?), there is growing risk of a turn to hotter and drier, during the summer growing season. However, within that preferred pattern, there is the risk of complexes of storms to provide intense short-term heavy rainfall and floods within a drier than normal pattern.“What this all means is this year the risk will be elevated for extreme weather and climate shifts which challenge outdoor activities such as gardening and farming.”The strength and duration of the La Niña will also be worth watching as we move through the growing season.“Research NOAA/NWS/Ohio River Forecast Center has done with Ohio State University and published at the National Weather Association Annual Meeting in 2008 showed La Niña years tend to be some of the most challenging for crops in Ohio,” Noel said. “Often times corn and soybean yields end up being at or below trend line. Corn is impacted more than soybeans.”I only have a few days of firewood left at the house (I do have a couple of truckloads of cut and seasoned wood elsewhere that I was planning on saving for next year). Unless I dip into next year’s supply, it seems that if the cold weather hangs on much longer I’ll have to fire up the propane furnace. I truly love all of Ohio’s 11 seasons — yes, even Mud Season. They each have their own appeal. But, like most of you, I am eagerly awaiting warmer days, planting season and the triumphant arrival of Actual Spring.