The Macromolecules

The Macromolecules - The Macromolecules The four major...

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The Macromolecules The four major classes of macromolecules are carbohydrates, lipids, proteins, and nucleic acids. Most macromolecules are polymers, built from monomers Three of the four classes of macromolecules—carbohydrates, proteins, and nucleic acids—form chainlike molecules called polymers. ° A polymer is a long molecule consisting of many similar or identical building blocks linked by covalent bonds. ° The repeated units are small molecules called monomers. ° Some of the molecules that serve as monomers have other functions of their own. The chemical mechanisms that cells use to make and break polymers are similar for all classes of macromolecules. Monomers are connected by covalent bonds that form through the loss of a water molecule. This reaction is called a condensation reaction or dehydration reaction. ° When a bond forms between two monomers, each monomer contributes part of the water molecule that is lost. One monomer provides a hydroxyl group (— OH), while the other provides a hydrogen (—H). ° Cells invest energy to carry out dehydration reactions. ° The process is aided by enzymes. The covalent bonds connecting monomers in a polymer are disassembled by hydrolysis, a reaction that is effectively the reverse of dehydration. ° In hydrolysis, bonds are broken by the addition of water molecules. A hydrogen atom attaches to one monomer, and a hydroxyl group attaches to the adjacent monomer. ° Our food is taken in as organic polymers that are too large for our cells to absorb. Within the digestive tract, various enzymes direct hydrolysis of specific polymers. The resulting monomers are absorbed by the cells lining the gut and transported to the bloodstream for distribution to body cells.
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° The body cells then use dehydration reaction to assemble the monomers into new polymers that carry out functions specific to the particular cell type. An immense variety of polymers can be built from a small set of monomers. Each cell has thousands of different kinds of macromolecules. ° These molecules vary among cells of the same individual. They vary more among unrelated individuals of a species, and even more between species. This diversity comes from various combinations of the 40–50 common monomers and some others that occur rarely. ° These monomers can be connected in a great many combinations, just as the 26 letters in the alphabet can be used to create a great diversity of words. Carbohydrates serve as fuel and building material Carbohydrates include sugars and their polymers. The simplest carbohydrates are monosaccharides, or simple sugars. Disaccharides, or double sugars, consist of two monosaccharides joined by a condensation reaction. Polysaccharides are polymers of many monosaccharides.
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This note was uploaded on 08/08/2009 for the course BIO 1406 taught by Professor Gomez during the Spring '09 term at Collin College.

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The Macromolecules - The Macromolecules The four major...

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