What If .. ?

What if cells started out without DNA? Sure, cells today are full of the stuff, but suppose that in the beginning, you just had these things that were just bags of metabolism? The basic dual-lipid-layer type cell membrane, enclosing a bunch of enzymes that run the Krebbs cycle or something? These early cells wouldn't have to do much, presumably they'd be floating in an environment rich enough in nutrients, all they'd have to do is just absorb them. Presumably also, the enzymes would be scarce enough, relative to the nutrients, that the entire environment wouldn't just metabolize itself out. All these DNA-less cells would have to do is absorb nutrients, expel waste products, grow, and when the surface area to volume ratio gets too low for efficient transfer, divide. Seems like something like that could form an ecosystem that could last a long time, if circumstances were right.

Then maybe, the odd bit of RNA or DNA could get trapped in some of these cells. It might not even do anything useful for the cell. Until the cell has an enzyme to duplicate it, you wouldn't even see the genetic material get amplified from division to division (though presumably, the enzymes to run the metabolism would already be getting reproduced, or daughter lines would just die when they ran out of these metabolic enzymes). Anyway, at some point, you'd find a cell containing both DNA (or RNA) and an enzyme that could duplicate it. Even if the DNA sequence produced no useful products for the cell, the cell would have to regulate, i.e., be able to switch on/off the reproduction of this DNA. Why? Assume there's no regulation. Either (A) the DNA isn't reproduced and some daughter lines cease to carry it, or (B) it is overproduced, and could kill the cell by virtue of just popping it .. sort of like a virus would do (hmm..), or (C) the cell could just get extremely lucky and produce just the right amount.

The reason I think metabolism preceeds genetics is just that, metabolic cycles are so much simpler compared to the processes involved in getting DNA duplicated, and especially when you consider that, unless some self-regulation is built in, getting it duplicated in the right amounts will be impossible, it just seems liklier that the simpler item came first. You can even see it as an evolutionary process, operating not at the level of DNA, but on the level of DNA: primeval DNA sequences that can't self regulate their own production either (a) fizzle out or (b) over produce and kill the cell, and so these don't tend to proliferate as time unfolds. Suddenly finding oneself in possesion of such unruly DNA is a sort of detrimental mutation, not within DNA, but at the level of "what the heck kind of chemistry should a cell include, anyway?".

On the contrary, a cell that finds itself host to DNA that can properly self-regulate at worst can be said to harbour a benign parasite, or you could call it a symbiosis, or you could view it as the birth of DNA based evolution, even if that genetic material isn't doing anything else useful for the cell, besides not killing it. Because, once well-behaved DNA exists like that, it's only a matter of time and useful mutation before that DNA starts doing something really useful for the cell, like producing more efficient enzymes for metabolizing different nutrients, or regulating the expression of enzymes to match changing conditions, and so on, in short, taking the bzillion or so steps necessary to become something that looks like a modern bacterium.