Sunday, December 5, 2010

Alternate Biochemistry

This topic was suggested to me by my awesome friend Thaddaeus Buser who is studying marine biology in Alaska.

Cool for four reasons: First of all, Someone reads my blog?! Awesome! Secondly, DUH. Aliens and extremophiles are my favorite thing to nerd out about…of COURSE I want to learn about hypothetical alien biology. Also, right in the middle of my research for this blog THIS hit the news. Relevant. Finally, remember that meatball looking cave alien in Star Trek the original series? That was my favorite alien in all of sci fi! It was called the Horta and a huge theme of that episode was that is was not carbon based, it had alternate biochemistry.

God, and that scene when Spock mind-melds with it and feels all it’s pain and suffering makes me want to cry every time. The only clip of it I could find on youtube has a bunch of fart sounds over it. Way to ruin a beautiful moment of cross-species connection, youtube jackass.

Here it is if you are curious.
But you should probably watch the episode Devil in the Dark sans fart sounds if you haven’t already.

Anyway, I’ll try to break this down with my meager knowledge of biology…

Life (as we know it) requires at least one cell. Cells need four things:
-carbohydrates (provide the cell energy)

-lipids (also called fats. They store energy and make up structures like the cell wall )

-proteins (the machines that do all the work of the cell. They are made up of amino acids, one of which is pictured here. )

-nucleic acids (DNA is a nucleic acid. It’s the master blue print that tells the proteins what to do.)

There is no need to fully understand what those diagrams mean, I certainly don’t. But I do know that the letters stand for elements and I see lots of C’s for carbon.

All four of these things have one element in common: Carbon. It’s what forms their backbones.

There are a few good reasons why life seems to have chosen carbon over any other element.

First of all, carbon’s main gig is forming compounds and carbon is good at what it does.

Here’s why:

Elements can bond with other elements via sharing electrons. All atoms want to have eight electrons in their outer shells and carbon only has four. That means it’s going to want to get close to other atoms and share electrons with them so that everyone has eight.

Having four slots for other atoms to go into makes carbon very versatile. It will bond with all kinds of stuff; hydrogen, oxygen, nitrogen…whatever, it’s not picky.  It helps that carbon is just the right size to nestle into lots of different kinds of molecules without pushing too much stuff out of the way.

Carbon will also readily bond with other carbon atoms to form long chains or rings. The bonds in these structures are strong and stable and carbon atoms can keep being added on to give you as big and complex a molecule as you need. 

This is important because it means we can make lots of different kinds of proteins which have all kinds of different functions. Remember, on the most basic level, proteins are what is doing all the work your body does and proteins with different arrangements of atoms will have different functions.

Here is a cool video I found of proteins doing lots of different jobs. My favorite parts are at 2:48 – 3:09 when they are all forming some kind of chain and then the severing protein comes and breaks it and at 3:41 when the motor protein comes walking by. It really walks along like that!

But seriously, proteins are the reason we can digest food, fight off illnesses, store memories, move our arms and legs…ect. Our body has about 50,000 different kinds all made up of carbons assembled into different combinations.

 And a final reason for basing life on carbon: there’s a lot of it. It’s the fourth most abundant atom in the universe because it’s easily made in the cores of stars.

 Welp, sounds like carbon is the right one for this job. But could any other atoms do the same sorts of things carbon does? Could life be based on something other than carbon?

Silicon might do the trick. Check it out, it’s right there underneath carbon on the periodic table.

 It’s in that spot because they both have 4 valence electrons…4 slots for other atoms to fill, so it will react (form bonds) with lots of the same stuff that carbon reacts with.

Just like carbon, silicon will form long chains with other silicon atoms. These are called silicates (the silicon analogy to carbonates). So a silicon based life form would have proteins that are made up of silicates instead of carbonates.

If silicon were to be the basis for a life form, lots of the molecules we know and love would be changed a little. For example, the carbon reactions take place when humans take in food and air would be silicon reactions. Allow me to explain: chemicals break apart and make new bonds inside our bodies to turn food into energy and air into whatever we get from oxygen (I don’t actually know, will someone tell me?). Our uh, “exhaust” gasses are carbon dioxide (We breathe it out. It’s a carbon and two oxygens: C02) and methane (FARTS. It’s one carbon and four hydrogens: CH4). Silicon can form very similar molecules: Silicon Dioxide (A silicon and two oxygens: SiO2) and Silane (A silicon and four hydrogens: SiH4). If a silicon based life form metabolized in similar ways that we do, by that I mean…eat food (as we know it) and breathe oxygen, then silicon dioxide and siliane would be some of it’s waste products in the same way that carbon dioxide and methane are our waste products.

Silane is what silicon based life forms might theoretically fart out, then. It’s what’s called pyrophoric, which means it will spontaneously burst into flames in the air! Can you imagine if that’s what farts were like??! It would be way harder to get away with, that's for sure. 

Silicon dioxide is what they might exhale. The thing about silicon dioxide, though, is that it’s a solid at earthly temperatures. It’s pretty too! Look:

It’s melting point is at 1,650 degrees Celsius, or 3,000 degrees Fahrenheit…HOT. So, silicon based life would either “exhale” a solid crystal, which might prove to be a bit of a respiratory problem, or maybe they would exist somewhere where the temperature is much hotter so the silicon dioxide could be in gas form. 

Here’s a cool picture of what the authors of the book, Extraterrestrials, A Field Guide For Earthlings thought that silicon based life might look like.

There are lots of used copies of this book on Amazon for a penny. I ordered one just cause I’m hoping it has lots of cool pictures. I’ll let you know if it’s worth the penny.

Following the reasoning that life is all about having four bonds, every element that is in the same column as carbon could theoretically be a basis for life.

However, there are some pretty serious problems with some of them.

Germanium, being the next one down, is a good place to start. Germanium COULD, theoretically, act like carbon. By that I mean, there is a germanium analogy to methane and carbon dioxide (germane and germanium dioxide), and germanium can also form long chains with itself. The pitfall is that germanium is RARE. Which makes sense, I mean…I never hear about germanium in anything, do you? This poses a problem because life needs LOTS of atoms. The likelihood of enough germanium atoms being in one place at one time to assemble into a cell, let alone a creature with trillions of cells, is pretty small.

However, germanium based life might be possible in the future! Heavy elements are fused in the cores of stars. As more and more stars die and new ones are born, the universe is getting more and more metallic. Maybe someday there will be enough germanium around to base life on it. Maybe life will slowly evolve to be based on heavier and heavier elements! Or maybe, due to the present state of the universe, we are in an era of life that will never occur again. Who knows?   

The next ones down the column: tin, lead and ununquadium (yes, that’s it’s name!) have the same abundance problems as germanium. There just isn’t that much of them around. Also, it’s hard to imagine how a life form based on such bulky elements would get around. I mean, think about being made of tin or lead…it would pose a pretty serious moving problem, wouldn’t it? I would think it would require lots of energy to move your body because it would be very heavy. Sounds like a pretty inefficient life form to me.

It has also been suggested that life could be based on nitrogen or phosphorus because these two atoms have the tendency to form long chains just like carbon. I couldn’t find out as much about these elements as a basis of life. The fact that no one has really done any google-able research on it makes me think that it’s probably not very likely, but I would love to hear about it from someone who knows more about biochemistry than me.

All in all, carbon seems to be the atom best suited for life, so it’s really no surprise that all the life we have ever heard of is carbon-based. Furthermore, it’s quite likely that carbon is the only element that can fill this role. I’ve heard people argue that it’s arrogant to assume that all life in the universe must be similar to life on Earth, but I really hate that argument. Here’s why: if we don’t make that assumption then we really don’t have much to go on. What are we supposed to be looking for if not what we know works? Perhaps life could be totally different than us elsewhere in the universe, but how would we recognize it if we saw it? And if we are going to make the argument that the basic chemicals of life are unnecessary, why not make the argument that most things attributed to life as we know it are unnecessary? For example, why should life require cells? I mean, when you think about it…our definition of “life” is pretty vague and sticky. Anything that is able to create offspring that are slightly mutated in order to better survive its' environment counts. Or more specifically, anything that evolves via natural selection. Using that definition of life, is a computer virus life? It certainly mutates and evolves. Is a crystal life? It grows and “reproduces” with altered offspring.

Life, it’s nature, it’s origin…everything about it, is obviously a major source of contention amongst the human race. I think religion is probably the most poignant example I can give here. But whatever you believe, I think it’s safe to say that no one understands life completely. All we can really do is speculate. Which is awesome because it’s a great chance to use those wonderful imaginations we’ve been blessed with!

Ok, well that’s enough nerding out for now. See you next time!


  1. "...PAIN...SUFFERING...the children...I AM THE GUARDIAN"

    Seriously, one of these days I'm going to throw a Classic Star Trek party and you will be the guest of honor.

  2. yeah!! You are the one who got me into it in the first place...