Fascinating: Ethanol is an alcohol

People have been drinking alcohol for a very, very long time. Ever since our very early forefathers learned the magic of fermentation, they’ve been churning out the stuff in its different forms. I suspect some of you reading this right now are drinking.

“Shots! Shots! Shots!”

According to the World Health Organization, the world drinks an equivalent of 6.1 liters of pure alcohol per person (as of 2005).  We enjoy them in copious quantities; sometimes too much, that the same report says that alcohol is responsible for 2.5M deaths a year.

That’s just half a liter. So imagine twelve times that. 

 As you may or may not know, there is more than one kind of alcohol (but you know that already). But ethanol is what we consume (and not other common alcohols like antifreeze, isopropyl alcohol, or methanol). Why is that? Thank or blame the enzyme alcohol dehydrogenase. It is responsible for helping you enjoy the buzz alcohol provides.

(Nice to know: Enzymes are proteins that speed up the rates of chemical reactions.)

Alcohol dehydrogenase is responsible for the conversion of ethanol (CH3CH2OH) to acetaldehyde (CH3CHO) in your liver. This reaction is shown below:

CH3CH2OH + NAD+ -> CH3CHO + NADH + H+.

(Nice to know: NAD+ is a coenzyme, they help in making the magic happen.)

This reaction produces acetaldehyde. Sounds harmless, problem solved? No, not really. Acetaldehyde is in fact more dangerous than ethanol. Why would the human body do that? Maybe because (you probably guessed it) there’s another another enzyme to convert acetaldehyde to something less harmful. Aldehyde dehydrogenase converts acetaldehyde (CH3CHO) to acetic acid (CH3COOH). If you have no idea what acetic acid is, try drinking a cup of vinegar.

Do it. Seriously.

Did you do it?  Congratulations, now you know what acetic acid is.  (On a related note, why would you drink a cup of vinegar just to prove this point?) Harmless, and in fact goes well with a lot of different kinds of food.

So in summary:

For all you science nerds. 

(Image from chemcases.com)

So now that alcohol has been converted to something harmless, you can now spend the rest of the day nursing your hangover.

Alcohol does wonders for the animal kingdom.

An interesting and fatal consequence of this process is what happens when you drink other types of alcohols. Methanol (CH3OH) is very similar to ethanol (CH3CH2OH) except that it has one less carbon.  You would think that would be unimportant, but the human body is a stickler for details. When ingested,  alcohol dehydrogenase being a dutiful enzyme that it is, converts methanol to formaldehyde.  Aldehyde dehydrogenase then converts formaldehyde to formic acid. You become blind, and maybe you die.

God forbid if this happens to you, get to a hospital quickly. On the way, drink lots of vodka. Ethanol competes with methanol for access to the alcohol dehydrogenase, preventing the formation of formaldehyde and formic acid.

Moral of the story: stick to the right kind of alcohol. Now go and enjoy a drink responsibly.

PS. Don’t drink and drive and more importantly, don’t walk home drunk (“…on a per-mile basis, a drunk walker is eight times more likely to get killed than a drunk driver.” Levitt and Dubner, SuperFreakonomics)

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References:

http://www.who.int/substance_abuse/publications/global_alcohol_report/en/index.html

http://www.users.csbsju.edu/~hjakubow/classes/rasmolchime/99ch331proj/alcoholdehydro/index.htm

http://www.pdb.org/pdb/101/motm.do?momID=13
http://www.alcohol-facts.net/history.jpg
http://pubs.niaaa.nih.gov/publications/aa72/aa72.htm
http://chemcases.com/alcohol/index.htm