The Last Lecture
Today we finished up by looking at the transamination reaction between alanine and alpha keto glutarate. The lesson was, as always, to show that complicated biological processes can typically be reduced to a series of elementary organic reactions.
To get your own copy of the biochemical processes wall poster that I showed in class, go to
this web site and click on the link at the bottom.
Keys have been posted.....
I have placed keys to exams 1, 2, and 3 to the right to go with the key to exam 4. Remember, Meaghen will have final exam review sessions on Saturday (1:30 - 3:30) and Sunday (6 - 8) in the Althouse lounge.
There is also a set of practice multiple choice questions.
Nucleic Acids
As we work our way to the end of the semester we are looking at bits and pieces of various topics. Today we looked at how ribose (or deoxyribose), sugars and ATP as a phosphoric acid equivalent can be used to make nucleic acids. It is just stringing together a number of known reactions.
Meaghen will hold two group study sessions this weekend: Saturday from 1:30 - 3:30 and Sunday from 6 - 8. Both sessions will be held in the Althouse lounge.
The class ended with a brief tutorial on polonium poisoning.
Pyridine, an Odd Aromatic Compound
Today we talked about pyridine, a somewhat strange aromatic compound. Pyridine is essentially a benzene ring with an sp2-hybridized nitrogen replacing one of the carbon atoms. With six ring electrons, the system is aromatic but the lone pair of electrons on the nitrogen is NOT part of the aromatic system. This gives pyridine more basicity than aromatic amines. However, since the orbital holding the lone pair is an sp2, with more s-character than the sp3-hybridized orbitals of aliphatic amines, pyridines hold the lone pair closer to the nuclei and are therefore less basic than aliphatic amines.
It is possible to perform EAS reactions on pyridine, with the electrophile ending up on the carbon with the largest partial negative charge (two carbons from the nitrogen, you can think of it as a sort of "meta" position). The reaction is typically of poor yield, as the nitrogen lone pair has a tendency to interact with the electrophile, not giving it a good opportunity to react with the ring.
A better reaction is the NAS (Nucleophilic Aromatic Substitution) of 2-halo pyridines. The electronegativity of the nitrogen allows for stabilization of the anionic intermediate, making the process viable.
