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CHAPTER 5 THE STRUCTURE AND FUNCTION OF MACROMOLECULES The topic of macromolecules lends itself well to illustrate three integral themes that permeate the text and course: 1 . There is a natural hierarchy of structural level in biological organization. 2. As one moves up the hierarchy, new properties emerge because of interactions among subunits at the lower levels. 3. Form fits function. I. Polymer Principles A. Most macromolecules are polymers Polymer = (Poly = many; mer = part); large molecule consisting of many identical or similar subunits connected together. Monomer = Subunit or building block molecule of a polymer Macromolecule = (Macro = large); large organic polymer - Formation of macromolecules from smaller building block molecules represents another level in the hierarchy of biological organization. - There are four classes of macromolecules in living organisms: 1. Carbohydrates 2. Lipids 3. Proteins 4. Nucleic acids Most polymerization reactions in living organisms are condensation reactions. Polymerization reactions = Chemical reactions that link two or more small molecules to form larger molecules with repeating structural units. Condensation reactions = Polymerization reactions during which monomers are covalently linked, producing net removal of a water molecule for each covalent linkage. - One monomer loses a hydroxyl (-OH), and the other monomer loses a hydrogen (-H). - Process requires energy. - Process requires biological catalysts or enzymes. Hydrolysis = (Hydro = water; lysis = break); a reaction process that breaks covalent bonds between monomers by the addition of water molecules. - A hydrogen from the water bonds to one monomer, and the hydroxyl
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bonds to the adjacent monomer. - Example: Digestive enzymes catalyze hydrolytic reactions which break apart large food molecules into monomers that can be absorbed into the bloodstream. B. An immense variety of polymers can be built from a small set of monomers Structural variation of macromolecules is the basis for the enormous diversity of life. - There is unity in life as there are only about 40 to 50 common monomers used to construct macromolecules. - There is diversity in life as new properties emerge when these universal monomers are arranged in different ways. II. Carbohydrates: Fuel and Building Material A. Sugars, the smallest carbohydrates, serve as fuel and carbon sources Carbohydrates = Organic molecules made of sugars and their polymers - Monomers or building block molecules are simple sugars called monosaccharides . - Polymers are formed by condensation reactions. - Carbohydrates are classified by the number of simple sugars. 1. Monosaccharides Monosaccharides = (Mono = single; sacchar = sugar); simple sugar in which C, H, and O occur in the ratio of (CH 2 O) - Are major nutrients for cells; glucose is the most common - Can be produced (glucose) by photosynthetic organisms from CO 2 , H 2 0, and sunlight - Store energy in their chemical bonds which is harvested by cellular respiration - Their carbon skeletons are raw material for other organic molecules.
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