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I need some help in what is a monomer?
There are four principal biological macromolecules which is protein, lipids, carbohydrate or nuclei
acid. A macromolecule is a giant molecule formed by joining a smaller molecule, usually by a
condensation reaction. Of these four types of molecules the carbohydrates is not always a polymer.
Am I on the right track.? Then what is a monomers of each of the three macromolecules that are
Looking forward to your reply.
read your chemistry book
There are more ways to make a polymer out of monomers than just condensation reactions, though in living systems, condensations are ubiquitous. In some sense all of the things you mention—proteins, nucleic acids, lipids, and carbohydrates—either are, or can be, polymers of something. In the case of proteins, amino acids are the monomers which are polymerized into peptides and proteins; individual nucleotide triphosphates are the monomers for DNA or RNA (nucleic acids); the term “carbohydrate” can be applied to both monomer and polymer—nobody says chemists are easy to get along with—individual sugars like glucose or galactose or ribose etc. are the monomers while pectin or starch or O- or N-linked glycopeptide carbohydrate moieties are polymers. Lipids are a bit more problematic depending on how you consider them. Some lipids can be constructed from “acetates” but the results are very plastic and it would be hard to identify the “monomer” in those cases. But things like the steroids or carotenes are built up from a five-carbon unit called isoprene, and, if you mentally break up the structure, you can usually recognize the five-carbon repeating units.
Lipids are not generally regarded as polymers, despite I totally see the reason behind your post, blcr11. Even some books i've read say "unlike large carbs and proteins lipids are large molecules that are not polymers". Some lipids are indeed polymers without doubt. Examples that come to mind are the plant lipids suberin and cutin.
I don't disagree with you MrMistery. I call lipids "problematic" in that sense. Some, as you say, are obvious polymers. Others are clearly made up of identifiable "monomeric" subunits which, in the case of the isoprenoids, for example, are even formed by repeated condensation reactions sequentially adding one five-carbon unit at a time (up to six, at which point the squalene molecule starts to cyclize and form the sterols). So no, typically you don't consider the lipids to be polymers, but under some circumstances you could.
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