@12:30, Tom’s instincts are right: saying DNA is ‘right handed’ and proteins are ‘left handed’ is all down to arbitrary ad-hoc conventions, sometimes with a hand-based mnemonic. For DNA, it’s actually the same convention as ‘righty tighty, lefty loosey’ for screws. For amino acids it’s a completely arbitrary thing based on the (also arbitrary) chemical priority of the molecules in a certain arrangement. Historically molecular chirality was assigned based on how the compound would rotate the polarisation of a beam of light, which goes back to the helical right-hand rule used for DNA, but this doesn’t match up with the molecular structural chirality that’s now used.
*Also* the laws of physics are actually non-chiral: the weak force only interacts with particles one way round. So there’s the intriguing, if implausible, possibility that this was what tipped the chiral balance in the development of life on earth.
The ‘righty tighty’ rule for helices in turn probably comes from the fact that the supinating motion of the hand is somewhat stronger than the pronating motion. So there’s some biological determination there, at least.
Thanks for the year’s experience and some basic statical nous and critical analysis which I hope I have absorbed! Have really enjoyed this and hope you have a great holiday. All the best, John.
@12:30, Tom’s instincts are right: saying DNA is ‘right handed’ and proteins are ‘left handed’ is all down to arbitrary ad-hoc conventions, sometimes with a hand-based mnemonic. For DNA, it’s actually the same convention as ‘righty tighty, lefty loosey’ for screws. For amino acids it’s a completely arbitrary thing based on the (also arbitrary) chemical priority of the molecules in a certain arrangement. Historically molecular chirality was assigned based on how the compound would rotate the polarisation of a beam of light, which goes back to the helical right-hand rule used for DNA, but this doesn’t match up with the molecular structural chirality that’s now used.
*Also* the laws of physics are actually non-chiral: the weak force only interacts with particles one way round. So there’s the intriguing, if implausible, possibility that this was what tipped the chiral balance in the development of life on earth.
The ‘righty tighty’ rule for helices in turn probably comes from the fact that the supinating motion of the hand is somewhat stronger than the pronating motion. So there’s some biological determination there, at least.
Thanks for the year’s experience and some basic statical nous and critical analysis which I hope I have absorbed! Have really enjoyed this and hope you have a great holiday. All the best, John.
Yesterday I’ve listened to episodes on Asteroids and Nuclear Winter, this episode is excellent addition to end the trilogy