UCM Chapter 11 Biochem

monosaccharides

• simple sugars

• building blocks

• aldehydes are called aldoses

• ketones are called ketoses

ketoses

aldose

nomenclature of carbohydrates

• Trioses – 3 carbon sugars (C3H6O3)

• Tetroses – 4 carbon sugars (C4H8O4)

• Pentoses – 5 carbon sugars (C5H10O5)

• Hexoses – 6 carbon sugars (C6H12O6)

• Heptoses – 7 carbon sugars(C7H14O7)

2^x = possibly # of sugars

x= # of chiral centers

• highest # chiral carbon defines chirality

glyceraldehyde

glucose

galactose

mannose

ribose

fructose

dihydroxyacetone

cyclic structures of monosaccharides

• Sugars with 4 or more carbons exist primarily in cyclic forms

• Aldehydes react with alcohols to form hemiacetals

• Ketones react with alcohols to form hemiketals

• Five and six member rings are the most common

anomeric carbon

starch

Homopolymer consisting of only glucose units • energy reservoir in plants • source of carbohydrates for humans • two polysaccharides occur in starch: amylose and amylopectin

amylose

• long unbranched chains of D-glucose residues • linked with α(1,4) glycosidic bonds • typically several 1000 glucose units • form long tight helices

amylopectin

branched homopolymer of glucose • contains α(1,4) and α(1,6) glycosidic linkages • branch points occur every 20-25 units • few 1000s to a million units

glycogen

carbohydrate storage molecule in vertebrates • greatest abundance is in muscles and the liver • contains α(1,4) and α(1,6) glycosidic linkages (same as amylopectin) • branch points occur more regularly • more compact for better storage

cellulose

composed of D-glucose units linked by β(1,4) glycosidic linkages • structural role in plants • most abundant organic molecule on Earth • we lack the enzyme to hydrolyze the β(1,4) linkages