Review Question 1 How many molecules of water are needed to completely hydrolyze a polymer that is 10 monomers long? 9

Review Question 2 After you eat a slice of apple, which reactions must occur for the amino acid monomers in the protein of the apple to be converted into proteins in your body? Amino acids are incorporated into proteins in your body by dehydration reactions

CARBOHYDRATES

Carbohydrates Serve as fuel and building material Include both sugars and their polymers (starch, cellulose, etc.)

Sugars Monosaccharides Are the simplest sugars Contain a single chain of carbon atoms with hydroxyl groups They also contain carbonyl (aldehyde or keytone) groups Can be combined into polymers

Examples of monosaccharides Triose sugars (C3H6O3) Pentose sugars (C5H10O5) Hexose sugars (C6H12O6) H C OH H C OH HO C H H C OH C O HO C H H C O Aldoses Glyceraldehyde Ribose Glucose Galactose Dihydroxyacetone Ribulose Ketoses Fructose Figure 5.3

Monosaccharides May be linear Can form rings OH 4C 3 2 H C OH HO C H H C O C 1 2 3 4 5 6 OH 4C 6CH2OH 5C H OH 2 C 1C 3 C 2C 1 C CH2OH HO 3 2 (a) Linear and ring forms. Chemical equilibrium between the linear and ring structures greatly favors the formation of rings. To form the glucose ring, carbon 1 bonds to the oxygen attached to carbon 5. Figure 5.4 The first (1) carbon is the carbon that has the carbonyl group attached to it.

α glucose vs. β glucose 50% of the time when glucose forms rings, alpha glucose is formed as opposed to beta glucose

Oligosaccharides – contain two or three monosaccarides attached by covalent bonds called glycosidic linkages Disaccharides Consist of two monosaccharides Are joined by a single glycosidic linkage

Figure 5.5 CH2OH O H H OH HO OH H2O Dehydration reaction in the synthesis of maltose. The bonding of two glucose units forms maltose. The glycosidic link joins the number 1 carbon of one glucose to the number 4 carbon of the second glucose. Joining the glucose monomers in a different way would result in a different disaccharide. Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose. Notice that fructose, though a hexose like glucose, forms a five-sided ring. (a) (b) H HO H OH OH O CH2OH H2O 1 2 4 1– 4 glycosidic linkage 1–2 glycosidic linkage Glucose Fructose Maltose Sucrose Figure 5.5

Polysaccharides Polysaccharides Are polymers of sugars with several hundred to several thousand monosaccharide subunits held together by glycosidic linkages Serve many roles in organisms

Storage Polysaccharides Chloroplast Starch Amylose Amylopectin 1 m (a) Starch: a plant polysaccharide Figure 5.6 Starch Is a polymer consisting entirely of glucose monomers Is the major storage form of glucose in plants

Two types of Starch Amylose Amylopectin Straight chain polymer of α (alpha) glucose Has 1-4 glycosidic linkages Amylopectin Branched chains of α glucose and β glucose Has 1-4 glycosidic linkages in the main chains and 1-6 glycosidic linkages at the branch points

Glucose Storage in Animals Glycogen Consists of glucose monomers Similar to Amylopectin (has 1-4 and 1-6 glycosidic linkages), but there are more branches in glycogen Stored in muscle and liver

(b) Glycogen: an animal polysaccharide Mitochondria Giycogen granules 0.5 m (b) Glycogen: an animal polysaccharide Glycogen Figure 5.6

Structural Polysaccharides Cellulose Is a polymer of glucose Has different glycosidic linkages than starch The main structural polysaccharide in plants and plant cell walls

Cellulose is a straight chain polymer of β glucose with 1-4 glycosidic linkages (c) Cellulose: 1– 4 linkage of  glucose monomers H O CH2OH OH HO 4 C 1 (a)  and  glucose ring structures (b) Starch: 1– 4 linkage of  glucose monomers  glucose  glucose Figure 5.7 A–C

Unlike amylose and amylopectin (starches), cellulose molecules are neither coiled nor branched Plant cells 0.5 m Cell walls Cellulose microfibrils in a plant cell wall  Microfibril CH2OH OH O Glucose monomer Parallel cellulose molecules are held together by hydrogen bonds between hydroxyl groups attached to carbon atoms 3 and 6. About 80 cellulose molecules associate to form a microfibril, the main architectural unit of the plant cell wall. A cellulose molecule is an unbranched  glucose polymer. Cellulose molecules Figure 5.8

Cellulose is difficult to digest However, it does contribute to “roughage” in the diet  fibre Cows have microbes in their stomachs to facilitate this process Figure 5.9

Chitin, another important structural polysaccharide Is found in the exoskeleton of arthropods Can be used as surgical thread (a) The structure of the chitin monomer. O CH2OH OH H NH C CH3 (b) Chitin forms the exoskeleton of arthropods. This cicada is molting, shedding its old exoskeleton and emerging in adult form. (c) Chitin is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals. Figure 5.10 A–C