Monday, October 24, 2005
Left Handed Crystals
Part of the reunion, one of the better ones, is what they call classes without quizzes--50 minutes of current Professors covering a topic of interest to them. Having been an English major with a minor in classics, I decided to go to a chemistry lecture about the origin of life. It was fascinating and you (or at least I) had to concentrate a bit to keep up with the chemistry Professor, Richard N. Zare, who is so smart they let him be a physics Professor too.
One of the cool things was when he passed around Quartz crystals which displayed mirror symmetry, that is, one was left handed and one was right handed in the twist of its formation. They were both of a simple chemical formula, SiO2, and absolute identical chemically--so why the different shape? Nearly half the quartz crystals in the world are right handed and the rest are left handed. What that meant to the Professor was that the starting point for the spin, the left or right handedness was absolutely random, but once it got started, the whole crystal had the twist. Self-organizing simple chemical compounds. One definition of life is self-organizing, self-replicating complex organic chemical compounds. Professor Zare's definition of life was that if you stepped on it and it stopped moving, it had, until recently, been life.
Here's how a very good Christian, Jonathan Sarfati, explains this stuff about right and left twist of compounds vital to life:
These two forms are non-superimposable mirror images of each other, i.e.: they are related like our left and right hands. Hence this property is called chirality, from the Greek word for hand. The two forms are called enantiomers (from the Greek word for opposite) or optical isomers, because they rotate the plane of plane-polarised light.
Nearly all biological molecules must be homochiral (all molecules having the same handedness. Another term used is optically pure or 100% optically active) to function. All amino acids in proteins are 'left-handed', while all sugars in DNA and RNA, and in the metabolic pathways, are 'right-handed'.
A 50/50 mixture of left and right-handed forms is called a racemate or racemic mixture. Racemic polypeptides could not form the specific shapes required for enzymes, rather, they would have the side chains sticking out all over the place. Also, a wrong-handed amino acid disrupts the stabilizing a-helix in proteins. DNA could notstabilizedised in a helix if even a small proportion of the wrong-handed form was present, so it could not form long chains. This means it could not store much information, so it could not support life.
So in review, the reason for the emphasis on the handedness was that DNA, RNA and many proteins have a helix that's right twisting. All of the amino acids in proteins twist left. No one really knows why that is, but it could be important.
Professor Zare felt that the origin of life took place in hot wet rocks for several reasons, the best of which is that the chemical substrate for RNA and DNA is a sugar joined with phosphorus, or more accurately with phosphate (PO4 to 3-), which does not occur often in liquid and almost never as a gas. So life almost certainly did not start on Earth (assuming it did) in the air and probably did not start in some warm shallow sea. HMMM. Completely the opposite of what was common knowledge even a few years ago.
More questions raised than actually answered but interesting and humbling. Like I said, classes without quizzes are a good part of the reunion.
One of the cool things was when he passed around Quartz crystals which displayed mirror symmetry, that is, one was left handed and one was right handed in the twist of its formation. They were both of a simple chemical formula, SiO2, and absolute identical chemically--so why the different shape? Nearly half the quartz crystals in the world are right handed and the rest are left handed. What that meant to the Professor was that the starting point for the spin, the left or right handedness was absolutely random, but once it got started, the whole crystal had the twist. Self-organizing simple chemical compounds. One definition of life is self-organizing, self-replicating complex organic chemical compounds. Professor Zare's definition of life was that if you stepped on it and it stopped moving, it had, until recently, been life.
Here's how a very good Christian, Jonathan Sarfati, explains this stuff about right and left twist of compounds vital to life:
These two forms are non-superimposable mirror images of each other, i.e.: they are related like our left and right hands. Hence this property is called chirality, from the Greek word for hand. The two forms are called enantiomers (from the Greek word for opposite) or optical isomers, because they rotate the plane of plane-polarised light.
Nearly all biological molecules must be homochiral (all molecules having the same handedness. Another term used is optically pure or 100% optically active) to function. All amino acids in proteins are 'left-handed', while all sugars in DNA and RNA, and in the metabolic pathways, are 'right-handed'.
A 50/50 mixture of left and right-handed forms is called a racemate or racemic mixture. Racemic polypeptides could not form the specific shapes required for enzymes, rather, they would have the side chains sticking out all over the place. Also, a wrong-handed amino acid disrupts the stabilizing a-helix in proteins. DNA could notstabilizedised in a helix if even a small proportion of the wrong-handed form was present, so it could not form long chains. This means it could not store much information, so it could not support life.
So in review, the reason for the emphasis on the handedness was that DNA, RNA and many proteins have a helix that's right twisting. All of the amino acids in proteins twist left. No one really knows why that is, but it could be important.
Professor Zare felt that the origin of life took place in hot wet rocks for several reasons, the best of which is that the chemical substrate for RNA and DNA is a sugar joined with phosphorus, or more accurately with phosphate (PO4 to 3-), which does not occur often in liquid and almost never as a gas. So life almost certainly did not start on Earth (assuming it did) in the air and probably did not start in some warm shallow sea. HMMM. Completely the opposite of what was common knowledge even a few years ago.
More questions raised than actually answered but interesting and humbling. Like I said, classes without quizzes are a good part of the reunion.
# posted by Roger Fraley @ 7:29 PM 
