In all life, and even in viruses, genetic information is always looking to replicate itself. I understand this. DNA carries information and seeks to replicate. Check. I have it down. The thing is, what is the physics behind this? DNA is made up of atoms; what is it about the quantum structure of DNA that makes it tend toward "reproduction" (even though more mass is not actually created)? i.e, what is it about the physics of DNA that allows it to "carry information" and makes it "want" to replicate?
Not really. That's a convenient way to describe how life functions, but it's not how the molecules actually work. I suggest you start at the wikipage for DNA replication. In a nutshell, DNA gets copied by enzymes into more DNA, or into RNA. RNA is then "read" by an enzyme and turned into proteins. The way DNA stores information is in the bases that make up the "rung" parts of the DNA "ladder". These bases (4 of them), have different chemical properties that can enhance the affinity of enzymes around them to bind it. For instance, certain sequences of DNA, called promoter regions, greatly increase the rate at which a transcription bubble will form. This is due to thermodynamics- the threshold of energy for binding is lowered due to the interactions between a certain sequence of bases and certain enzymes. In the case of RNA, which is the stuff that's actually used to build proteins, sets of three bases at a time, called codons, call for amino acids, the building blocks of proteins. Why do some amino acids only bind certain codons and not others? Again, because of thermodynamics. The energy required to bind some codons is much lower than others, so only certain enzymes bind and that way the correct protein is built. Why use DNA & RNA? DNA is quite stable for a large organic molecule, but presumably harder to read, since it is kept double stranded and bunched up inside the nucleus much of the time. It might be safer to make copies of it and move the copies rather than reading directly from the DNA itself. Or it could just be a product of evolution- more on that in a bit. RNA has an extra oxy group attached, which makes it very reactive, and quite unstable. This is alright for a short term messenger molecule, but trying to store info on it for long would be bad. It also has the ability to cleave itself, meaning that it can cut itself up. Even double stranded RNA is considerably more reactive, due to those oxy groups that DNA lacks (hence DEOXYribonucleic acid- the D in DNA). As for evolution and why RNA is read to make protein and not DNA, there's a growing body of evidence that proto-life consisted of self replicating, self reactive RNA molecules, that could perform both the functions of DNA (info storage) and of enzymes (copying and protein production). Over time, the RNA got better at recruiting proteins, and gave rise to cellular life- RNA reactions in little soap bubbles. DNA may have been a convenient, and safe, way to store information in relatively hostile environments. Early earth had a lot of UV radiation before an ozone layer was formed due to photosynthesis creating an O2 atmosphere. Making a couple copies of RNA from DNA, then reusing those RNA strands to make lots of protein may have reduced the amount of time DNA was exposed when it was opened up and "read". Alternatively, it could simply be that the RNA reading enzymes that make proteins- I'll give them their proper name- ribosome- were so well developed by that time, switching to a DNA reading enzyme would be entirely too costly to fitness. Ribosomes are the most conservative sequence of genomic information across all known life forms- you can synthesize proteins encoded on human DNA in jellyfish, mice, pigs, fungus, or bacteria. They evolved very down low on the family tree, and haven't changed much since then, all things considered.
Please note, I am no physicist, but.... Is there any need to involve quantum physics to explain DNA replication? I doubt there is. I can’t see any quantum effects at play and would think that “traditional” physics and chemistry is all that is required.
Another important thing to remember is base pairing. That is there are 4 bases but an adenine on one chain is always paired with a thymine on the other chain and guanine is always paired with cystosine. So each single chain contains full information on the sequence. This immediately leads to the possibility of DNA replication.
....because replication of double stranded DNA is semi-conservative – one strand acts as the template for the synthesis of a new strand.
Thanks for the answers, but I already knew all of that. What I am asking is WHY does this base pairing and all these factors work in the way they do?
Well, judging by your first post, you DIDN'T know any of that. You seemed to have a very rudimentary understanding of the process. But why does it work the way it does? Thermodynamics. The hydrophobic nucleotide cores of DNA helps keep the strands together in an aqueous environment, while the base pairing that occurs (A matching T, G matching C) does so because A and T base pairing is thermodynamically more stable than A and G base pairing or T and C.
No one knows. Older and more knowledgeable scientists will tell you this, young ones who know less but like to think they know everything will try to answer. We don't know why DNA does what it does, we know some things about the behavior of what it does, and what it is. But not the "why". It took a guy on an acid trip to figure out the double helix and how it was structured. Literally he was very high on LSD when he discovered it.
I believe you are referring to the discovery/invention of the PCR chain reaction for duplicating strands of DNA to make usable quantities for identification purposes. That insight occurred while he was engaged in a LSD trip, he says. The DNA helical structure was discovered without usage of mind-altering drugs, I believe.
