Talk:Polymer
|
|
Proteins are not polymers. The amide linkages of protein molecules have pendant groups that do not repeat and as such are not chains of repeating monomer units. The chain lengthening process for polyamides is also far more sophisticated and exact than is the polymerization of monomers. tRNA shuttle amino acids to growing polypeptides according to the template DNA strand, while addition polymerization is governed primarily by statistical considerations and is driven by large concentration gradients. Industrial polymerization catalysts do not offer the fantastic control over the polymer chain sequence that the cellular machinery does over the polypeptide sequence, and likely never will. For these reasons, the classification of proteins (or polypetides) as polymers is misleading and inaccurate.
-KC
That is really a matter of definition. A more broad term sometimes used is macromolecule. Some people prefer to save the term polymer for chains similar to what we can create synthetically and prefer to put species such as proteins and DNA into the larger category of macromolecules. I don't think it is fair to pull proteins out of the polymer category strictly because of their propagation method. Polymeriization includes many different propagation methods, some providing more control over the propagation than others. Certain forms of living polymerization may soon allow us to control specific addition to polymer chains in similar fashion to the protein construction. In fact, a lot of research is going into making our own proteins. I believe that currently it is possibly, but incredibly slow (i.e. a few monomer units per hour). That being said, there are some other reasons to classify non-polymer macromolecules. Exactly what those are is still a good discussion.
TM
Personally I think the analogy between biopolymers and regular polymers is fine. Other biopolymers, such as starches (polymerized sugars) or the isoprenoids (see isoprene for a classic polymeric unit in a biological context), seem neglected in this article and the remarks on proteins are such that the author believes all proteins are enzymes or transport proteins. Not all are. Some are purely structural proteins, and the notion of active region (isn't the more precise term an active site?) versus structural region is meaningless in this context. Of course, structural proteins are often evolutionarily scavenged enzymes (classic example being the crystallins of the eye, which tend to be derived from various and sundry proteases), so maybe it isn't all that important ;) Dwmyers 18:03, 18 Sep 2003 (UTC)
Proteins are polymers, they're just block copolymers with many different monomers, and very small blocks :) TM - we can already synthesise custom polypeptides, eg via the polystyrene tethered approach of the Merrifield synthesis (http://www.schoolscience.co.uk/content/5/chemistry/proteins/Protch4pg1.html) (for which the 1984 Nobel Prize was awarded). Iridium77 00:17, 9 Mar 2004 (UTC)
Although vandalism is bad and I do not like, I must admit I laughed out loud when I read "dog shit is a common polymer that people like to eat". Well done, whoever put that, it was quite funny (at least I thought so) but don't do it on wikipedia please... Borb 22:49, 8 Apr 2005 (UTC)
Nylon
If memory serves correctly the nylon example is inaccurate - the more reactive acid chloride is used and hydrogen chloride gas the byproduct. --ThomasWinwood 00:12, Apr 19, 2005 (UTC)
There are actually different routes to synthesize nylon. The example where the polyamide is synthesized with the acid chloride is called the "Schotten-Baumann" reaction. It's a form of "interfacial polymerization", also known as a "two phase reaction". It's extremely fast - the reaction rate is 104 to 108 times faster than the mechanism suggested on the page. But, acid chlorides are rather expensive, so its usually used when there are no other routes for synthesis available. However, I think the way the reaction is outlined on the page is misleading, and more work can be done in terms of illustrating the displacement and elimination of the small molecule correctly. HappyCamper 04:13, 19 Apr 2005 (UTC)