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CHAPTER 5 - THE STRUCTURE AND FUNCTION OF MACROMOLECULES Introduction Cells join smaller organic molecules together to form larger molecules. These larger molecules, macromolecules , may be composed of thousands of atoms and weigh over 100,000 daltons. The four major classes of macromolecules are: carbohydrates, lipids, proteins, and nucleic acids. A. Polymer principles 1. Most macromolecules are polymers Three of the four classes of macromolecules form chainlike molecules called polymers. Polymers consist of many similar or identical building blocks linked by covalent bonds. The repeated units are small molecules called monomers . Some 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 via a condensation reaction or dehydration reaction . One monomer provides a hydroxyl group and the other provides a hydrogen and together these form water. This process requires energy and is aided by enzymes. The covalent bonds connecting monomers in a polymer are disassembled by hydrolysis . In hydrolysis, as the covalent bond is broken a hydrogen atom and hydroxyl group from a split water molecule attaches where the covalent bond used to be. Hydrolysis reactions dominate the digestive process, guided by specific enzymes. 2. An immense variety of polymers can be built from a small set of monomers Each cell has thousands of different 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 other rarer ones. These monomers can be connected in various combinations, like the 26 letters in the alphabet can be used to create a great diversity of words. Biological molecules are even more diverse. B. Carbohydrates - Fuel and Building Material Carbohydrates include both sugars and polymers. The simplest carbohydrates are monosaccharides or simple sugars. Disaccharides, double sugars, consist of two monosaccharides joined by a condensation reaction. Polysaccharides are polymers of monosaccharides. 1. Sugars, the smallest carbohydrates serve as a source of fuel and carbon sources
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Monosaccharides generally have molecular formulas that are some multiple of CH 2 O. For example, glucose has the formula C 6 H 12 O 6 . Most names for sugars end in - ose . Monosaccharides have a carbonyl group and multiple hydroxyl groups. If the carbonyl group is at the end, the sugar is an aldose, if not, the sugars is a ketose. Glucose, an aldose, and fructose, a ketose, are structural isomers.
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This note was uploaded on 12/14/2009 for the course BIOCHEM bIO taught by Professor Professor during the Spring '09 term at École Normale Supérieure.

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