chapter05 - Chapter 5. THE STRUCTURE AND FUNCTION OF...

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Chapter 5 . THE STRUCTURE AND FUNCTION OF MACROMOLECULES. Small molecules have unique properties arising from the orderly arrangement of its atoms. The major groups of biologically important molecules are carbohydrates, lipids, proteins and nucleic acids. Usually they are very large containing thousands of atoms: macromolecules. Macromolecules are giant molecules formed by the union (bonding) of smaller molecules. They consist of hundreds of thousands of atoms. This is another level of biological organization. POLYMERS Most macromolecules are polymers. These are long chains formed by linking small organic molecules called monomers. Polymerization is the linking together of monomers to form polymers. It takes place through dehydration reactions. 1. Condensation is the chemical process by which monomers are linked together. A molecule of water is removed: dehydration synthesis . Each of the two monomers forming the bond contributes one part of the water molecule, the hydroxyl group [–OH] and the hydrogen [–H]. 2. Hydrolysis is the chemical process by which polymers can be degraded into monomers. A molecule of water is broken into H and OH and added to the broken bonds. Each molecular product receives a hydroxyl group or a hydrogen. Hydrolysis is the reverse of condensation (dehydration synthesis). A infinite number of polymers can be built from a limited number of monomers. Each class of polymer (e. g. lipids, proteins, etc.) is formed from a specific set of monomers. Proteins (polymer) are made of thousands of amino acid units (monomer). The uniqueness of organisms depends on the unique arrangement of the same monomers. Macromolecules are constructed from only 40 to 50 common monomers and some others that occur rarely. CARBOHYDRATES Carbohydrates include sugars and their polymers. Carbohydrates contain carbon hydrogen and oxygen in a ratio of 1:2:1 or [CH 2 O] n .
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Monosaccharides are simple sugars. They serve as sources of energy and carbon atoms. Normally containing 3 to 7 carbon atoms. A hydroxyl group is bonded to each carbon except one. That carbon is double bonded to an oxygen atom forming a carbonyl group; depending on the position of the carbonyl group, the sugar is an aldehyde (aldose sugars) or a ketone (ketose sugars). Glucose is an aldose and fructose a ketose. Most sugar names end in -ose . Dissaccharides are made of two monosaccharide units. Two monosaccharide rings joined by a glycosidic linkage , a covalent bond formed between two monosaccharides by a dehydration reactions. They can be split by the addition of water, hydrolyzed. Maltose is formed by linking two glucose monomers and sucrose by linking one glucose and one fructose. Glucose linked to galactose produces lactose, the sugar in milk.
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This note was uploaded on 02/05/2011 for the course BIO 311C taught by Professor Satasivian during the Spring '08 term at University of Texas at Austin.

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chapter05 - Chapter 5. THE STRUCTURE AND FUNCTION OF...

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