This is a complex molecule so I'm not going to insist on the IUPAC name. You can supply a common name as long as it is unambiguous (be careful!). This time it's not sufficient to just give me the name of the molecule. You also have to briefly explain what it does and where you can find it, including the "species." The functional explanation has to be a biochemical explanation.
Post your answer in the comments. I'll hold off releasing any comments for 24 hours. The first one with the correct answer wins. I will only post correct answers to avoid embarrassment.
There could be two winners. If the first correct answer isn't from an undergraduate student then I'll select a second winner from those undergraduates who post the correct answer. You will need to identify yourself as an undergraduate in order to win. (Put "undergraduate" at the bottom of your comment.) Every undergraduate who posts a correct answer will have their names entered in a Christmas draw. The winner gets a free autographed copy of my book! (One entry per week. If you post a correct answer every week you will have ten chances to win.)
After today, you have only one more chance to win an autographed book.
Some past winners are from distant lands so their chances of taking up my offer of a free lunch are slim. (That's why I can afford to do this!)
In order to win you must post your correct name. Anonymous and pseudoanonymous commenters can't win the free lunch.
Winners will have to contact me by email to arrange a lunch date.
UPDATE:The molecule is β-D-glucopyranosyl-5-hydroxymethylcytosine. This is a modified base found in T4 bacteriophage and its relatives. The modification is required to protect phage DNA from E. coli host restriction endonucleases.
The winner is Bill Chaney.
Nov. 2009: Jason Oakley, Alex Ling
Oct. 17: Bill Chaney, Roger Fan
Oct. 24: DK
Oct. 31: Joseph C. Somody
Nov. 7: Jason Oakley
Nov. 15: Thomas Ferraro, Vipulan Vigneswaran
Nov. 21: Vipulan Vigneswaran (honorary mention to Raul A. Félix de Sousa)
Nov. 28: Philip Rodger
Dec. 5: 凌嘉誠 (Alex Ling)
1. Yes, I know it's Wednesday. I was too busy on Monday to post a molecule.