B.3.1 Describe the structural features of monosaccharides
- monosaccharide means "one sugar"
- all contain a C=O (carbonyl group) and at least two -OH (hydroxyl groups)
- empirical formula is CH2O
B.3.2 Draw the straight-chain and ring structural formulas of glucose and fructose
Straight Chain
- candidates responsible for drawing only D-isomers (not L)
Straight Chain
Ring Structure
- there exists alpha and beta isomers of glucose and fructose
- alpha-glucose exists when the -OH group on carbon 1 and carbon 2 are on the same side in ring structure, and beta-glucose exists when the -OH group on C1 and C2 are on opposite sides
- for fructose, there is first the distinction between fructopyranose rings (which are hexagonal in shape), and fructofuranose rings (which are pentagonal in shape)
- the difference between pyranose and furanose is that with pyranose, 5 of the 6 carbons are directly part of the hexagonal ring shape, whereas with furanose only 4 of 6 carbons are directly part of the pentagonal ring shape
- the alpha forms exist when the CH2OH group is on the same side as the -OH of carbon 3, and the beta forms exist when the CH2OH and -OH group of carbon 3 are on opposite sides
B.3.3 Describe the condensation of monosaccharides to form disaccharides and polysaccharides
Examples:
- monosaccharides combine to form disaccharides via a condensation reaction
- a hydroxyl group from one monosaccharide and a hydrogen from the other detach and form water as a byproduct
- carbon 1 on one monosaccharide linked to carbon 4 on the other
- called glycosidic linkage
Examples:
- monosaccharides: glucose, fructose, galactose
- disaccharides: maltose (a-glucose + a-glucose), sucrose (a-glucose + a-fructose), lactose (b-glucose + b-galactose)
- polysaccharides: starch (a-glucose), glycogen (a-glucose), cellulose (b-glucose)
B.3.4 List the major functions of carbohydrates in the body
- glucose is an energy source
- when we have excess glucose that our body doesn't immediately need to burn away, it is stored in energy reserves as glycogen
- carbohydrates are also precursors for other biologically important molecules, such as glycoprotein sequences linked to antibodies
B.3.5 Compare the structural properties of starch and cellulose, and explain why humans can digest starch but not cellulose
- both are polysaccharides formed from glucose units
- starch has 2 different forms: amylose is a straight chain polymer with alpha-1,4 linkages while amylopectin is a branched polymer with both alpha-1,4 and alpha-1,6 linkages
- cellulose has beta-1,4 linkages
- both starch and cellulose require enzymes to be broken down, but the enzyme that catalyzes cellulose, which is cellulase, can't be found in humans
B.3.6 State what is meant by the term dietary fibre
- dietary fibre is mainly plant material that is not hydrolyzed by enzymes secreted by the human digestive tract but may be digested by microflora in the gut
- e.g.) cellulose, hemicellulose, lignin, and pectin
B.3.7 Describe the importance of a diet high in dietary fibre
- dietary fibre may be helpful in the prevention of conditions such as diverticulosis, irritable bowel syndrome, constipation, obesity, Crohn's disease, hemorrhoids, and diabetes mellitus