- (a)(i) Lactose: Constituent monomers are glucose and galactose. One role in living organisms: carbohydrate source in mammalian milk.
- (a)(ii) Sucrose: Constituent monomers are glucose and fructose. One role in living organisms: form in which sugars are transported in plants.
- (b) The bond that joins two monosaccharides in a disaccharide is a glycosidic bond.
- (c)(i) In the hydrolysis of lactose, the missing component in the left-hand box (galactose) is a six-carbon sugar with an aldehyde group at C1 and hydroxyl groups on other carbons; the right-hand box (glucose) is also a six-carbon sugar with an aldehyde group at C1 and hydroxyl groups on other carbons, differing in stereochemistry at C4.
- (i) The chemical reaction that joins monosaccharides together to form an amylose molecule is a condensation reaction (dehydration synthesis).
- (ii) One structural difference between amylose and glycogen is that amylose is a linear polymer of glucose linked by α(1→4) glycosidic bonds, while glycogen is highly branched with both α(1→4) and α(1→6) glycosidic bonds.
- (iii) Two ways in which the structures of amylopectin and glycogen make them suitable for energy storage are: (1) their branched structure allows for rapid enzymatic access and release of glucose units during hydrolysis, and (2) their compact, coiled structure minimizes space occupied per unit of stored glucose.
- (iv) Amylase catalyzes the hydrolysis of starch into maltose. The structure of starch consists of amylose (linear chains of glucose linked by α(1→4) glycosidic bonds) and amylopectin (branched chains with α(1→4) and α(1→6) glycosidic bonds).
- (v) A cellulose molecule differs from starch in that cellulose is composed of β-glucose units linked by β(1→4) glycosidic bonds, forming straight, rigid chains that can hydrogen-bond with adjacent chains to form strong microfibrils, whereas starch is composed of α-glucose units linked by α(1→4) and α(1→6) glycosidic bonds, forming helical or branched structures that are more easily digested.
Parent Tip: Review the logic above to help your child master the concept of chemistry of carbohydrates worksheet.
