01_Biomolecules - Biomolecules - 1 - BIOMOLECULES CONCEPTS...

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Biomolecules - 1 - BIOMOLECULES CONCEPTS CHECK LIST INTRODUCTION There are four major classes of biomolecules: carbohydrates, lipids, proteins, and nucleic acids. Monomers can be polymerized into long polymers. Polymers can be classified as homopolymers (made from many identical monomers) or heteropolymers (made from combinations of different monomers. Much of the variation in the structure and properties of polymers is due to the use of different monomers. Most polymerization reactions are condensation (dehydration) reactions that release a molecule of water as each monomer is added. Polymers can be disassembled by hydrolytic reactions that consume water. Most biological macromolecules are polymers formed by polysaccharides, proteins, and nucleic acids. CARBOHYDRATES Carbohydrates include the simple sugars (monosaccharides) and their polymers (disaccharides, oligosaccharides, and other polysaccharides). Monosaccharides (esp. glucose) are major cell nutrients and monosaccharides (together with their breakdown products) are used for making many other types of molecules within cells. Monosaccharides are classified according by the number of carbon atoms and the chemical nature of the carbonyl group (aldoses and ketoses). Monosaccharides can form many different structural and geometric isomers, each with unique characteristics. Most monosaccharides form alternative ring structures when placed in aqueous solution. Alpha and beta glucose are structural isomers that differ in the arrangement of the hydroxyl group at C1. Disaccharides and oligosaccharides consist of two or a few monosaccharides respectively, each monomeric unit joined to another by a glycosidic linkage. Storage polysaccharides such as starch and glycogen are used by plants and animals respectively for storing energy in the form of glucose units that can be released by hydrolysis for use as a cellular fuel and for synthesizing many other types of molecules. Starch and glycogen are helical molecules. Amylose and amylopectin are the two main forms of starch. Amylose is a linear molecule, whereas amylopectin and glycogen are branched. Structural polysaccharides perform support functions in organisms. The hydrolysis of cellulose requires cellulases, enzymes that are lacking in most organisms. A herbivore is able to digest cellulose by virtue of cellulases released by microorganisms present in its gut. Starch, glycogen, and cellulose are homopolymers of glucose, whereas chitin is a homopolymer of N-acetylglucosamine (GlcNAc).
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Biomolecules - 2 - LIPIDS Lipids are organic molecules that are more soluble in nonpolar solvents than in water. Lipids include fatty acids, glycerides, fats, oils, waxes, steroid hormones, and most nonprotein membrane components, including phospholipids and cholesterol.
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01_Biomolecules - Biomolecules - 1 - BIOMOLECULES CONCEPTS...

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