Back in 2001, I proposed that the original cells, used to seed this planet, contained the ability to form “viretes.” The basic idea is that the virete would function something like a gamete, but instead of transmitting genetic information across time to future generations, it would transmit genetic information across space to facilitate the survival of the founding group (see my discussion on cross-talk ) by connecting them. Here is how I put it back in 2001:
Actually, I have been toying with the idea that viruses were designed (keeping in mind that I view viruses as non-living, life-dependent phenomena and not organisms). I would speculate that viruses were originally designed to allow the designed cells to cross-talk extensively. More specifically, I envision cells designed with the program to disperse part of their genetic constitution laterally through a life-cycle-like stage that involved replicating and packaging genetic material for dispersal. In short, I speculate that what we now know as ‘viruses’ were originally a designed sex-like mechanism for unicellular organisms, important for establishing a foothold on a sterile planet (I call them viretes). Possible expressions of this mechanism might include:
a. A cell suicide program coupled to the packaging of genetic material for dispersal.
b. An endospore-like program, where instead of forming a spore around the replicated DNA, the DNA is packaged in virus heads which in turn are packaged into a “release” cell.
c. Controlled exocytotic release.
I would further speculate that such sex-like mechanisms may have been important in the early stages of the designed founder effect allowing the heterogeneous cells to adjust, as a consortium, to an unfriendly environment. During this adjustment phase (analogous to the latent phase in a bacteria growth curve), the cells shuffled their material and hit upon global-adaptive state whereby the importance of such transfer was decreased. We still see “rusty remnants” of this state carried on by the vestiges of transposons, natural transformation, and yes, viruses.
Well, almost 10 years later, it’s looking like I was on to something:
Let’s return to Lake’s new hypothesis about the origin of double-membrane bacteria:
Here, by analysing the flows of protein families, I present evidence that the double-membrane, Gram-negative prokaryotes were formed as the result of a symbiosis between an ancient actinobacterium and an ancient clostridium.
Since actinobacteria and clostridia might represent cells very similar to the original cells, let’s have a look at them. First, consider actinobacteria.
I’m not sure how I missed this one. Recall that only one of a million randomly generated codes was more error-proof that the genetic code used by life. Well, in turns out the frequency of amino acids used by all three domains of life is much the same. And when you factor for this frequency of amino acid use, the genetic code is actually much better than “one in a million”:
We found that taking the amino-acid frequency into account decreases the fraction of random codes that beat the natural code. This effect is particularly pronounced when more refined measures of the amino-acid substitution cost are used than hydrophobicity. To show this, we devised a new cost function by evaluating in silico the change in folding free energy caused by all possible point mutations in a set of protein structures. With this function, which measures protein stability while being unrelated to the code’s structure, we estimated that around two random codes in a billion (10^9) are fitter than the natural code. When alternative codes are restricted to those that interchange biosynthetically related amino acids, the genetic code appears even more optimal.
[Gilis D, Massar S, Cerf NJ, Rooman M. 2001. Optimality of the genetic code with respect to protein stability and amino-acid frequencies. Genome Biol. 2(11):RESEARCH0049]
The Seeding Story and Spawning Story have a different story to tell. The former begins with a consortium of sophisticated, complex cells while the latter begins with a simple self-replicating molecule able to co-opt from a huge assortment of potentially useful chemicals in the thick prebiotic broth. Does it really make sense to think such two radically different starting points cannot leave any traces that would help us distinguish between the two?
Posted in LUCA, seeding
Tagged LUCA, seeding
Your body depends on a continuously moving stream of blood in order to stay alive. Why? Because it is the blood which carries the oxygen needed to fuel the electron transport chain in the mitochondria of all your cells. The continuous movement of the blood, thanks to the heart, coupled with the continuous supply of oxygen to the blood, thanks to the lungs, means all of the body cells have the ability to continuously generate ATP by their mitochondria. And that ATP is needed to run the variety of molecular machines inside the cells.
But the liquid portion of the blood, the plasma, can only dissolve and carry about 3% of the body’s oxygen demand. The other 97% of the oxygen must be carried by the blood transport protein, hemoglobin. Hemoglobin is composed of four amino acid chains known as globin, each one with a red pigment molecule known as heme embedded inside. The heme binds on ionized form of iron, which in turn is where the oxygen binds. Every red blood cell is packed with hemoglobin, thus oxygen.
What this all means is that your large, complex, multicellular body exists because of the globin protein. It is the globin, with its ability to bind, hold, and release oxygen that facilitates its existence.
Aha! I had a couple of essays saved from a few weeks back……
Most arguments about the origin of life are sucked into the domain of the Traditional Template. In other words, we are once again treated to the old arguments whereby people dispute whether or not it was possible for geochemical processes to spawn biological processes. But I think it is more interesting to approach this topic while looking for clues – facts about the world we might expect to find if a given hypothesis is true.
The Seeding Story and Spawning Story have a different story to tell. One begins with a consortium of sophisticated, complex cells while the other begins with a simple self-replicating molecule able to co-opt from a huge assortment of potentially useful chemicals in the thick prebiotic broth. Does it really make sense to think such two radically different starting points cannot leave any traces that would help us distinguish between the two?
As I just argued, if the Earth was seeded with single-celled organisms that were rationally designed, we can safely assume the cells were designed in such a way that the chances for a successful seeding were enhanced. We can safely assume this because beings intelligent enough to design a cell that front-loads evolution would design cells that were likely take root on the ancient Earth.
A strategy that I proposed would be using a hetergenous consortium of cells that were connected by a deeper unity. I outlined my logic in that introductory posting, but let me add to it.
Posted in seeding