How did the first cell develop?

Ok…I’m trying to understand how life could had evolved from non-living material. I accept that it did somehow, but the mechanism by which it could had came about seems mind boggling.

What sequence of events must had occured in order to arrive at the first cell capable of repoduction and survival? What came first and what came last?

Was it necessary to develop the RNA (or DNA) prior to formation of a cell membrane? Was it necessary to have ribosomes before the RNA (DNA)?

When did reproduction come in to the scene (probably asexually initially)? And how would reproduction be possible without DNA or telemeres?

If everything that has to happen has to happen pretty much at that same time, it seems nigh impossible that life would ever had gotten started. The reproduction part is the part that is really throwing me for a loop. I don’t see how reproduction could had taken place without many other processes already being developed. But without reproduction, all of those processes would had to have been developed in a single organism first.

Any help?

No one knows for sure, but the best guess is that life was around in the form of replicating molecules long before anything resembling a cell came around. Does that shed a little light on the question?

…And it’s currently believed that that replicating molecule was a lot like RNA.

In the early-Earth oceans where life (presumably) originated, it wasn’t too important to have differentiated cells, with membranes or walls to separate themselves from the rest of the world. Back then, the entire ocean had a composition much like the interior of a cell.

The highest probability is that cells developed in some tidal pool rich in nutrients, fed by sunlight, tidal variations, and time time time.
Time = millions of years or more.

It also helps to think about mitochondria as evolving by themselves and incorporated into a cell (a little cell used by a big cell so to speak).

It has been a few years, but when I was in school, the most logical hypothesis that I encountered was that within the primordial ooze that sparked life, random interactions of ions, proteins, and other molecules (replicating and not) resulted in changes within the ooze that surrounded certain groupings of the flotsam and jetsam. These changes, through time, caused gradients of saturation levels of things like water, and crude nutrients/wastes. The differentiation continued and eventually led to the development of basic structures that were precursors to membranes. Once symbiotic relationships start to develop between the flotsam and jetsam and ooze (that is seperated from the rest of the ooze by a crude membrane), amoeba-like blobs start to morph in and out of existance, picking up random bits and smaller amoeba-like blobs, or being swallowed into larger ones. Structures that would later become chlorophyl and motochondria may have formed in this way. In the presence of selective pressures (temperature, availability of resources), competition, survival of the fittest…plus enough time and viola…you have a cell.

If you put some phospholipids in water and shake them up, they’ll form cell membrane-like structures called mycells (or micells, depending on who you talk to).

For an excellent discussion on the subject, read “At Home in the Universe” by Stuart Kauffman.

God did it.

Replication was definitely the first step. Indeed, it is a determining factor of life.

In an environment with the composition and conditions the primordial earth is thought to have had, compounds like amino acids, nucleotides, and other simple organic molecules can be spontaneously formed. This has been demonstrated in the lab. It is also known (or strongly suspected – it’s been a while since I had this class) that certain RNAs possess self-replicatory abilities. Now, if, in a global ocean filled with a soup of these organic preliminaries for millions of years, just one of these self-replicating RNAs develops – and remember that an RNA is just a polymer of simple organic molecules – then you’re set. It will, by definition, replicate, and soon you’ll have an ocean full of these suckers.

And they don’t have to be particularly good at their job, either. At this early stage, they have no competitors or predators, so if they only do a fairly good job of replicating themselves, their population will grow larger. And, of course, since they’re so poor at their job, there will be mistakes in the replication. Most of the mistakes will be much worse at their job, but a small few will be better. Once again, by definition of their nature as replicators, those that do a better job of reproduction will come to dominate the environment. And as things start to get more complex, you can start incorporating other aspects. As has been mentioned, it is a natural process of phospholipids to form membranes. No work has to be done to achieve this, it is a natural low energy state. So replicator RNAs can start incorporating lipid membranes with very little work, they just have to start utilizing something already present in the environment. Also, amino acids are naturally present, and could be utilized by the RNAs to make proteins – molecules that are much more flexible and efficient at catalyzing reactions for the replicators. Eventually, most of the replication jobs are handed off to the proteins (although RNAs are still vital components in replication – rRNA, tRNA, etc.), and the genetic material changed from RNA to DNA, a more stable material. Then about a zillion other complicated chemical processes have to occur to form your modern cell, which is why, although it’s expected that life formed 3.5 billion years ago, complicated organisms didn’t form until 550 million years ago. I.e., for three billion years, life was made of simple cells working out the complicated steps necessary to accomplish things like photosynthesis, the Krebs cycle, the electron transport chain, the genetic code, etc. and etc. and etc. Before even attempting to do simple things like slap a few cells together into an organism. Modern cells are truly remarkably complicated and intricate machines.