Originally posted November 12, 2010
Asteroids? Lightning? Hydrothermal Vents? Minerals? Fancy Gold Reactors?
November 12, 2010
I’m sitting here and I don’t know how to start this article. For whatever reason, I am feeling anxious. Who knew that writing for all of your relatives could be so nerve-wracking. (My mom is one of 17 kids … so seriously, I think I might actually be related to all of these people.) The anxiety I am experiencing is caused by the release of proteins by my body. It may be just this specific protein but it’s more likely that the feeling of anxiety is brought on by the release of lots of different proteins.
Proteins are big, complicated molecules, made up of building blocks called amino acids. Proteins make up our muscles. Proteins help us digest food. Proteins help us see. Proteins play a primary role in everything we do. To give you an idea of how complicated proteins are, I thought I’d invite a couple of proteins over to our post:
“Hi! I’m a protein. I do things. I make amino acids that your body can stitch together to make more proteins.” (pdb code: 1MAP – for those cool kids in the know)
“Hi! I’m a protein. I do things too. I make proteins. I take all sorts of amino acids and put them together as per the instructions of your DNA.” (pdb code: 1SFO)
“Well, um, hi Mr. and Mrs. Protein. Uh where the heck did you guys come from?” No, seriously. Look at those monstrous molecules. How in the world did they ever come into existence? These certainly are not methane (CH4) or nitrogen (N2). This is a really interesting question with no clear answer as to how proteins started to come into being. At least with evolution we have a fossil record. No such luck when it comes to the chemistry for how proteins first started to come together.
Hominid skull fossils. The fossil evidence showing evolutionary advances is present as opposed to the chemical evolution in the creation of proteins. (There’s no controversy surrounding human evolution, right?) (Image source)
So, the first basic question is, “Where do amino acids (protein building blocks) come from?” To answer this, scientists need to be able to recreate the conditions (atmospheric composition, temperature, pressure, etc.) that were on earth before any organisms (plants, animals, bacteria, archaea) started to evolve. Turns out that, for amino acids, this is an easy question to address. Amino acids are found in all sorts of places that you would not expect to find them. If you’ve got some carbon-based molecules, some nitrogen and some oxygen, with the right kind of energy sources, you are bound to get some amino acids. Amino acids have been found in meteorites. Scientists have been able to make amino acids from dust surrounded by ice crystals – mimicking conditions you would find in space – (here and here. subscription required – sorry). You can even heat the bejeebers out of some un-intimidating molecules enclosed in a gold tube and produce amino acids.
The trickier question is in trying to determine how these molecules went from being just amino acids to linking up and making big, functional proteins. Again, scientists need to be able to recreate the environment of pre-creepy-crawly earth in order to come up with a reasonable explanation for why amino acids started linking up to form proteins.
One answer may come from the research of Robert Hazen of the Carnegie Institute for Science. (An excellent articleby Helen Fields in the Smithsonian Magazine profiles Dr. Hazen and his work.) Hazen thinks that minerals (quartz, diamond, calcium carbonate, hematite, etc) were the key in bringing amino acids together so that they could react to form proteins. It turns out that the surface of calcite (calcium carbonate/limestone) is great at absorbing amino acids. This will bring the amino acids close enough to react with one another. However, it is still unknown what conditions are necessary to promote protein synthesis in this kind of environment. And, if scientists can coax out some “bio”-synthesis, they would still need to determine if the methods needed to do so seem plausible.
So, while these ubiquitous rocks may have been enough to bring amino acids together, scientists are still looking to find reasonable conditions that can develop this:
The amino acid valine.
and some other stuff … into this
[WARNING!! Science in progress …]
(I can’t help it … my kids are cute)
Mind that gap!
Hazen and other researchers like him are ultimately detectives, trying to put together clues that uncover the way that Nature works. It is clear to see how exciting working in a field like this can be. An engaging problem with endless possibilities, the chemistry of “how” we came to be will be inspiring scientists for a long time to come.
-mrh