Dr. Bortrum
05/01/2015
Anniversaries and Cells Chatting
CHAPTER 56 Communications and Junctions
At last! Our winter of repeated snow and ice storms is over and spring has sprung. The flowers and trees are in full bloom and I have already carded three rounds of golf at our local par-3 course. For us in the northeastern USA, it's hard to believe that this past March was the hottest March in the years of record keeping dating back to the 19th century. Editor Brian Trumbore called my attention to a graphic put out by NOAA showing the temperature profiles around the globe and our northeastern area was one of a handful of colder than normal regions on an Earth crammed with hotter than normal temperatures.
As I began writing this column some weeks ago, I saw an item in the news about a 66-year-old fellow, escaped convict Clarence David Moore, who had just turned himself over to authorities after nearly 39 years of being on the lam. The reason for turning himself in? He wanted the health care! Coincidentally, within a few minutes of running across that news item, I logged on to an email from The Electrochemical Society (ECS). The email contained a reference to another, more reputable Moore, Gordon Moore, of the famed Moore's Law originally proposed by him 50 years ago in a paper published in April, 1965. Moore stated that the number of electronic components on a silicon chip would double every year (later revised to 18 months or two years). This "law" has in a real sense driven the semiconductor industry until today there are literally billions of transistors on a silicon chip, with the price per transistor dropping to a tiny fraction of a cent. For better or worse, this achievement has spawned the communications-happy world we live in today.
Speaking of communications reminds me of an article in the May issue of Scientific American titled "Cellular Small Talk" by Dale Laird, Paul Lampe and Ross Johnson. Over the years, I've often been intrigued by articles on trees or plants "communicating" with each other. For example, I recall reading somewhere that certain trees, when attacked by insects chewing up its leaves or digging into its bark, emit a chemical signal of some sort that warns other trees in the area of the threat or the tree might start making a chemical that attracts predators that eat the insects threatening the tree's existence. It's as though the tree has some sort of intelligence to ward off its enemies. The Scientific American article discusses how communication takes place on the cellular level.
Gordon Moore's law is based on devices employing p-n junctions. Until I read the Scientific American article, I had never heard of a "gap junction" or of molecules called "connexins" (my spellchecker also hasn't heard of connexins). When a cell meets another cell, the surfaces of the cells flatten where they bump together. Naturally, when you bump into someone, you want to talk to them. Same thing with cells. How do they talk with one another? By exchanging ions or small molecules of certain compounds . How do these ions or compounds get through the interface where the cells are in contact? A logical way would be to form a channel or channels between the cells. This is where connexins come into the picture. Connexins, as pictured in the article, remind me somewhat of a hairpin but more complicated in shape with a curly section.
If six connexins get together in that flattened section of the cell they form an elongated structure with a more or less hexagonal hole in the middle. The hole is called a "hemichannel" and if a hemichannel from one cell lines up with a hemichannel from the other cell, a complete channel is formed through which ions and small molecules can flow between the two cells. The cells can talk to each other. More than one of these channels form the gap junction between the cells.
Now comes the mindboggling stuff. Take the heart, which contains billions of cells. A single gap junction between two of the heart's cells can contain some ten thousand channels! We've said that each channel involves two hemichannels, each with six connexins. That means we have about 120,000 connexin molecules in each gap junction! But wait, we're not finished. In our heart, our cells are not just talking to one other cell. They're in contact with other cells so there's more than one gap junction for each cell. So, we have our heart with all these zillions of gap junctions. We're finished, right? Would you believe that half those gap junctions are replaced every two hours and chances are in the course of a day essentially all of the cardiac gap junctions are torn down and new ones are formed.
I won't attempt to discuss other aspects considered in the article but suffice to say that studies have shown there are many different types of connexins and that mutations in connexins can be related to various diseases. When I started writing these columns and, for most of my scientific career, the scientists that impressed me most were theoretical physicists and quantum mechanicians. However, in my later years I've stood in awe of those who study life and the biological and chemical processes and characteristics that are involved in living creatures. A simple living cell is an incredibly complex entity. I liked the last sentence of the article : "What exactly are cells whispering to one another and how do these molecular secrets govern the assembly and operation of complex creatures - including ourselves?"
Of course, concerning life, a fundamental question is how did life begin? Naturally, I was intrigued when I saw the title of an article by Robert Service in the March 20 issue of the journal Science - "Origin-of-life puzzle cracked". For life to begin and procreate the premise is that there must have been something akin to DNA or RNA in order to pass along the codes for life to continue. In order to get life going and keep it going there had to be nucleic acids (RNA and/or DNA), amino acids and lipids. It's been a question as to whether and how these three types of compounds could have arisen in the primordial "soup" on Earth back billions of years ago. A favored scenario is that it was RNA that was first involved in the process. John Sutherland at the University of Cambridge and colleagues showed in 2009 that at least a couple of the building blocks for forming RNA could be formed from acetylene and formaldehyde, two relatively simple compounds.
Skeptics complained that acetylene and formaldehyde weren't that simple and where did they come from. This criticism prompted Sutherland and colleagues to see if they couldn't produce acetylene and formaldehyde from even simpler compounds. Now they report in the journal Nature Chemistry that if you take hydrogen cyanide (HCN) and hydrogen sulfide (H2S) reacting under ultraviolet (UV) light with various catalysts and under different conditions, the precursors to RNA, amino acids and lipids can be formed. The hydrogen cyanide could have come from comets striking Earth. Note that the Rosetta mission recently detected hydrogen cyanide on the comet above which it is orbiting and where Rosetta's lander is down on the surface. Sutherland points out that the various compounds may not have formed in the same
Finally, this seems to be a good year for anniversaries. I've mentioned Moore's Law's 50th. I noted in an earlier column that this year marks the 100th anniversary of Einstein's general relativity theory. The Hubble Space Telescope has been in orbit sending back those spectacular pictures for 25 years. On a sobering note, we just "celebrated" the 40th anniversary of the final days of the Vietnam war. I had the feeling that I may have an anniversary of sorts this month and went to the Bortrum archives on this site. Sure enough, I posted my first column on May 12, 1999 so I've been writing these columns for 16 years. It's been an exciting time in the field of science what with such things as the detection of hundreds of new planets, deciphering of DNA and finding its junk is not junk, new findings of intelligence in birds, the Higgs boson, oceans on moons of planets in our solar system, etc., etc. And could a recent study on the effect of ultrasound on Alzheimer-like symptoms in mice possibly translate eventually to a cure for Alzheimer's in humans? I should live so long!
Next column, hopefully, on or about June 1.
Allen F. Bortrum
