Molecule formation (amino acids ) and life

Factual Questions
1

Its my understanding that the amino acids were the first to form and are the building blocks of life on earth (Am I right ?). Here are my questions related to this :

1> So why amino acids - what is so special about them ? Are there other molecules that could have originated life ? I know carbon can form chains but so can Silicon. Could we have had silicon based life forms if conditions were different ?

2> Is it necessary to have complex molecules to have intelligence or life ? How small can the molecules be as we know it today for the simplest life forms - say viruse

2

Not really. We really don’t know what molecules were in the first living things. I think the most preferred theory now is that the key component was some sort of nucleic acid, but probably not DNA as we know it today: maybe RNA or something chemically similar.

Amino acids are formed relatively easily under the sort of conditions believed to have prevailed on the early Earth, though, and they are the building blocks of proteins, which are certainly a key component of all living things today (well, a few viruses don’t contain protein, but viruses are, arguably, not really alive), and proteins are a pretty versatile sort of molecule, that can do lots of things, so it is a possibility that the first self-replicating molecules that gave rise to life were proteins, made from amino acids, and the nucleic acids got involved later.

They are the components of proteins which, as already noted, are a key component of all the living things we know about, and do most of the “work” involved in keeping a cell alive.

As noted above, maybe nucleic acids such as RNA. Maybe it could be done with other types of organic (carbon) compounds that we don’t know about, but there are no obvious likely candidates.

It is conceivable, but not very likely. Although it does better than the other elements in this regard, silicon is probably not capable of forming molecules as large, complex and various as we know that carbon can.

Yes. The macromolecules in viruses, that make them alive (if they are alive) are of the same general type (nucleic acids and proteins) and complexity as those in other living organisms, such as human beings. The virus will have fewer actual molecules in it, and fewer types of protein and nucleic acid molecule, but the molecules themselves are of the same order of complexity.

It is questionable whether viruses are truly alive, because they cannot reproduce by themselves without a living cell of a more complex type of organism to infect (and they do very little except infect cells and then reproduce). The first living things cannot have been viruses, or much like viruses. Viruses are a later development that must have evolved after cellular life had established itself.

3

Than you njtt for the detailed answer. It answers many of my questions and I still do not understand what is special about amino acids, so let me ask it a different way : What other molecules could do the same job as amino acids ?

4

Well, you can’t make proteins without amino acids because if something is not made of amino acids it is not a protein, by definition.

Your question should be, I think, what other sorts of molecules could do the jobs done by proteins? The answer is, we really don’t know (but possibly none). Proteins are extremely versatile and play very many roles in a living cell.

It is conceivable that in some alien type of life there might be another sort of organic (carbon based) molecule, apart from proteins, that could do the same sorts of jobs that proteins do in the living organisms we know about, but we do not know what those other sorts of molecules might be. Proteins (and nucleic acids) are the only sorts of molecules that we know about that will do the jobs they do. However, the possible types of large organic molecules are endless, so there might be something that we have never yet seen that might work (or maybe not).

5

I would like to dig a level deeper than that. Say for example - Soaps do the job they do because for soap to work, you need a long molecule with one end attracted to oil and the other end attracted to water - so salts of fatty acids, Sodium tri-poly phosphate etc work great as soaping agent. So whats it about Amino acids / Nucleic acids that make them so good for their jobs ?

6

Proteins don’t do just one job, they do thousands of different jobs. There are twenty different amino acids (there could potentially be more, but life-as-we-know-it really only uses 20) that can be assembled in any order into long, long chains to make different proteins with a huge variety of chemical and physical properties. We do not know of any other class of molecules with that sort of versatility, and which could also be encoded into an organism’s genetic inheritance in the way that protein structures are encoded in DNA.

What DNA does, basically, is to store the blueprints for making the proteins we need to live, and RNA’s job is to ensure they actually get made. They are useful molecules for life because they can encode a lot of information reliably.

7

About a decade ago, there were two camps: RNA first and Protein first. Both camps had very good arguments why the other side had to be wrong.

My (wild) guess is that it was something else first, or at least, amino acids and proto-proteins along with that something else. More recently, there was some optimism about the slimy surface of clay as having good properties for early life to develop (rather than some “primordial soup”). But I never heard enough details on that, at least, nothing dumbed down to my level.

The bottom line is that currently, there is not a good scientific theory or even a plausible hypothesis for the origin of life. Much to the delight of creationists, of course, but if you pin your hopes on what we don’t know, they’ll be dashed if we figure it out.

It’s really tough to imagine life working without a cell membrane, and it’s tough to imagine a cell membrane that would preceed life. But it’s possible that natural (nonorganic) bubbles could form that could provide some kind of interior/exterior division.

There are countless chicken-and-egg problems. I’m hoping someone here is really up on the latest, as origins is a fascinating topic. Unfortunately it’s filled with many dead ends and few live ones.

8

I think I understand the op’s question a little bit better. The structure of an amino acid is special in the sense that you have your generic-found-in-living-things acid, carboxylic acid group. And you also have the same thing in the form of a base, being a amine group. If you ask someone who has never studied chemistry or biology, they may think that an amino acid is an oxymoron because you have both a proton acceptor and a proton donor in the same molecule. Specifically at a physiological pH, both the proton acceptor and the proton donor are ionized, creating a Zwitterion.

This causes amino acids to be extremely versatile, allowing it to do jobs and connect to other molecules (amino acids usually) that would be difficult. And to answer your other question, the only molecule that can do the same thing would have to be a zwitterion at physiological pH and also be simple in structure enough to be stable inside of a living machine.

9

Thank you Almost Perfect. That was a perfect reply to what I was looking for.

10

The Phospholipid bilayer is thought to have once been a single phospholipid layer, and phospholipids are fatty acids.

Fatty acids are relatively simple and sometimes naturally occurring chemicals. Because these molecules can have one end that is attracted to water, and another end that is repelled by water, they can form discrete layers, all facing the same way.

In my college biology course, the most current theories at the time were that naturally occurring acids, in conjunction with the action of water droplets forming and evaporating in certain environments, led to things like lipid layers which completely surrounded water molecules. Such layers would be permeable to other chemicals but would generally retain water.

As such, it was a non-organic and naturally occurring “blob” of water that could contain other chemicals.

By itself, that does nothing and is not life. But it is possible for such a thing to form naturally, without any biological process.

Within this protective layer, is possibly the only place on earth that the complex chemical reactions required by RNA and DNA-based life could safely happen, an environment which was at least somewhat naturally homeostatic.

Those blobs of acids and water, would serve as a vehicle for amino acids to interact.

Amino acids are also simple structures and are naturally occurring, simply because their structures are made of common chemicals found on earth, and they’re naturally capable of forming into those structures simply by being in proximity to one another.

Given a combination of amino acids which can form proteins and occur naturally, given non-organically formed fatty acid layers encased in water, and given enough time and exposure to different environments and chemicals, it’s possible a single chemical formed naturally that reacted to form more complex chemicals out of other amino acids to make proteins.

It’s still a far cry from being alive, because the chemical would also need to be able to replicate itself, as well as there would probably need to be some mechanism for generating lipid layers around the primordial cell.

However, even I can see where the building blocks of a cell could form independently, and then come together through non-organic processes. How that turns into nucleic acids and how the more complex elements of the cells formed, that involves a bit too much chemistry for me to follow it.

I’m not even sure I fully understand this layer of current theory, but to me, if you can explain where lipids come from, demonstrate how they form layers that are attracted to or repelled by water, demonstrate where amino acids come from, and put this all in an aqueous solution, I can see the basic building blocks coming together.

None of this spontaneously turns into life without some missing pieces, but it covers a lot of ground I thought was completely improbable before learning about it.