Anyone know Manfred Eigen's reason for...

...there being four DNA molecules instead of two? In Darwins Dangerous Idea, Dennett mentions that he (Eigen) has an idea as to why but he (Dennett) isn't going to say what it is and we should be able to guess. If I could read this book in the time it takes me to read a novel - and understand it - that might be true for me. All I can guess is that it affords DNA the ability to take the shape it does because of some of the other things in this section of the book.

TheAmazingPinball wrote

...there being four DNA molecules instead of two? In Darwins Dangerous Idea, Dennett mentions that he (Eigen) has an idea as to why but he (Dennett) isn't going to say what it is and we should be able to guess. If I could read this book in the time it takes me to read a novel - and understand it - that might be true for me. All I can guess is that it affords DNA the ability to take the shape it does because of some of the other things in this section of the book.

Because with four molecules you can fit more data in less space. It's kinda like if I gave you the choice to write a book in binary code (using only one or zero as letters) or just regular letters. Obviously by using regular letters you can fit more information in less space.

Or we could go the theistic route and say four is a magic number... oooohhhhh!

No way! That's what I thought of first! I was thinking it'd have to be twice as long to code that way. Then I started thinking about binary too and it's just 1's and 0's. I started second guessing myself thinking that I must be wrong because binary would be inferior and not used if you could fit more with four. However, the binary reader is different from the DNA reader. Plus C goes with G and T goes with A which, not really knowing a hell of a lot about this stuff, made me think that that would be essentially the same information storage-wise as just two. But then this is all in a physical space and the shapes of these molecules carry information too. Unless I am misunderstanding that.

My understanding was that since adenine (A) forms a base pair with thymine (T), and guanine (G) forms a pair with cytosine (C), that there are only 2 "values" on DNA, AT or GC. If there were 4 molecules that could bond to any of the others there would be 10 possible "values" (AA AT AG AC TT TG TC GG GC CC), but this isn't the case.

GaryM wrote

My understanding was that since adenine (A) forms a base pair with thymine (T), and guanine (G) forms a pair with cytosine (C), that there are only 2 "values" on DNA, AT or GC. If there were 4 molecules that could bond to any of the others there would be 10 possible "values" (AA AT AG AC TT TG TC GG GC CC), but this isn't the case.

Yes that is true. So not knowing if it matters which side a molecule is on (AT as opposed to TA), I don't know if it's an information storage issue. And for all I know, since it matters in at least one direction on the x axis it could matter on the y. If it does not matter, then one combination of molecules could be the eqivalent in binary of 01 and the other would be 10. So that would make them equal in terms of information storage.

Now, since (according to Dennett - I haven't read anything else about this so it's my only source) molecular shape carries information too (I may have misunderstood this point) it would be an information storage issue but by what I am thinking of as a different means.

I'm dog-paddling for my life.

[DrunkMonkey]

The only way you could have two molecules would be if they paired with themselves, like 1-1 and 2-2 so that you could copy the strand and still have the same information. If codons were still 3 bases long, you could only encode 8 different amino acids (2^3) rather than 20 (4^3 minus duplicate codons). If codons were longer, everything would just get really complicated.

[DrunkMonkey]

TheAmazingPinball wrote

Yes that is true. So not knowing if it matters which side a molecule is on (AT as opposed to TA), I don't know if it's an information storage issue. And for all I know, since it matters in at least one direction on the x axis it could matter on the y. If it does not matter, then one combination of molecules could be the eqivalent in binary of 01 and the other would be 10. So that would make them equal in terms of information storage.

Now, since (according to Dennett - I haven't read anything else about this so it's my only source) molecular shape carries information too (I may have misunderstood this point) it would be an information storage issue but by what I am thinking of as a different means.

I'm dog-paddling for my life.

It doesn't matter if it is T-A or A-T because when DNA is replicated, the strands are split and then new strands are built onto them.

A-T

A T
A-T T-A

Yup DrunkMonkey is right. 4 bases (ATGC) in codons of 3 is the smallest number necessary to code for the 20 odd amino acids. He is also correct about replication but that only applies during cell mitosis (reproduction). For protein production only one of the two sides is used and only that side never the other. The reason is that one side will end up reading as nonsense or stop codons before anything is produce.

[DrunkMonkey]

GradualStudent wrote

Yup DrunkMonkey is right. 4 bases (ATGC) in codons of 3 is the smallest number necessary to code for the 20 odd amino acids. He is also correct about replication but that only applies during cell mitosis (reproduction). For protein production only one of the two sides is used and only that side never the other. The reason is that one side will end up reading as nonsense or stop codons before anything is produce.

I was wondering about that as I typed my post. I knew that it must read off of one side, but I didn't know how it worked. I should go read more of my textbooks.