Alternate chemistries of life and updates

After months of working on it, our paper is finally submitted. Now all we have to do is wait for the rejection (I’m kiddingūüė¨).

In other news, ES3001 Astrobiology began last week. I’d say its going well. Last week was good; this week I thought was questionable. I’m disappointed because Tuesdays lecture didn’t go as smoothly. I thought I was ready, but I found myself stuttering and I rushed through the material. I hope to do better on Thursday. The bright side of rushing on Tuesday is that it leaves me more time on Thursday when we discuss alternate chemistry of life. This was a topic a lot of them had interest in, so I’m hoping to use the extra time to fluff it up a bit using the papers mentioned in the book.

With that in mind, lets talk about the chemistry of life!

Carbon as a backbone of life

Lets start with the basics.

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CHNOPS are the six major elements life uses. Of course, life uses other elements in other ways, but these are the main ones we care about.

Carbon of course is the back bone of life. Carbon is ideal because it forms stable bonds with a number of elements, but these bonds, while stable, are still sufficiently weak to allow for them to break when needed. It can form double and triple carbon bonds which encourages increased diversity in the type of molecules it forms. Of course, it can also form long chains, or polymers, as life is prone to do.

Silicon is often considered an alternate to carbon. It lies below Carbon in the 14th column of the periodic table which allows it share several characteristics with carbon. Silicon is more reactive than carbon. That is to say, the bonds break more easily and require less energy. It has a nature to share and accept more electrons than carbon, and can form more bonds. This means the diversity of molecules it can form is even higher thna carbon. However, all this makes the bonds very polarized.

All in all, the lack of stability may make life harder to maintain itself because the compounds are less stable. Silicon is also larger, so some things become harder like ring compounds or double/triple bonds as with carbon. Finally, it forms rocks with oxygen.

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A more likely chemistry with silicon might be a hybrid with carbon, called Silanes. They are made up complex silicon and hydrogen bonds which can substitute of organic groups allowing for more stability, but they are not very common in natural world.

However, the biggest problem with silicon is the availability of oxygen which is one of the most abundant elements in the solar system.

Other sources have their own problems too. Germanium is the same as Si. Halogens (Cl/F) too unreactive. Metals form weaker ionic bonds (opposed to covalent). Then oxygen and boron are too readily bonded to carbon which is abundant.

Water as the solvent of life

Life needs a solvent because the molecules of life need a liquid to react in. Something that can allow for high enough concentrations but also allow them to move around easily. Obviously, water meets this requirement. Its polar; the easiest way to think about it is like a magnet. It makes it easy to dissolve salts and organics which are useful to life.

It also has the benefit of taking a lot of heat to change its temperature (this changes for different liquids). It makes it more stable and useful in controlling temperature (i.e. evaporate cooling by sweat). Of course, water is also special because ice floats. If it sank, it would allow lakes to freeze much more quickly, killing life.

Life could use other solvents. They each have their own caveats. I don’t have a lot of time to expand on this, so I will leave it with a table. I may come back to it to elaborate when I have more time.

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Phosphorus in DNA and possible alternatives.

My apologies, this is another thing I don’t have time to discuss very much. However, phosphorus is a key part of DNA where phosphate links together sugars to form the backbone of DNA. This backbone is what the bases or letters of life link to. Some have suggested the earliest forms of life used Arsenic, but that its less stable to hydrolysis.