Parity Code And DNA

jnana writes "There's an interesting article in Nature about error-correcting parity code in DNA. It seems that there are enzymes that check for even-parity nucleotides (according to a 0 and 1 assignment scheme in the article) and recognize odd-parity nucleotides as errors. The authors argue that this parity scheme is the reason that adenine, thymine, cytosine, and guanine became the building blocks of nucleotides instead of other types of purines and pyrimidines that must have coexisted with them."

Comments

Parity schmarity

[nebbian]

This sounds to me of another case of "If you look for something hard enough, then you'll find it". In actual fact there is no parity checking there at all.

Parity checking (in computers) involves adding up the number of 1's in a byte, and putting another bit on the end purely as a form of error control. In even parity there are always an even number of 1's in the (byte + paritybit).
In the article they've figured out that cytosine has 1 donor, and guanine has 2 donors. Then they invent the whole parity thing by letting cytosine equal 1 and guanine equal 0, and when you add all the numbers together you get an even number of 1's. Sounds like circular reasoning to me.
If there was a regular parity bit in the DNA to make sure that an even number of G's or A's occur every 8 or so pairs, then fair enough! But what the article is describing isn't the same parity as you get on your serial port.

It's like saying "Let all starfish with 5 arms equal 1, and all starfish with 6 arms equal 0. Add the numbers up and bingo we've got even parity! Nature is a computer!"

Stinks of looking for more funding to me.

natural selection?

[cheezehead]

From the article:

Natural selection picked out the chemical basis of genetic information transfer probably because it was the best of the available options for ensuring fidelity in reading and copying information.

Assuming that they mean "selection" as in an evolutionary sense, I fail to see how this can be true. Isn't the whole genetic chemistry (ATCG, DNA, etc.) necessary before any selection can take place at all? In other words, isn't this a chicken-and-egg problem? You need a self-replicating structure before you can have reproduction, which is necessary for selection (right?). Or are we to believe that there was once a whole slew of competing chemicals, and our good friends A,T, C, and G won the grand prize because they had a 'parity check'? But even if you buy into that, where did the repairing enzymes come from? Aren't enzymes encoded by... (drumroll...) DNA? I'm a bit out of my area of expertise here (I ain't no biochemist), but it does seem a bit strange to me...