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Biology 12 McIntyre. Biological Macromolecules: Carbohydrates See Chap 1.2 in your text: Biology 12. Carbohydrates. Major source of energy from our diet Most abundant organic compounds in nature Serve both as structural compounds and as energy reserves to fuel life processes
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Biology 12McIntyre Biological Macromolecules: Carbohydrates See Chap 1.2 in your text: Biology 12
Carbohydrates • Major source of energy from our diet • Most abundant organic compounds in nature • Serve both as structural compounds and as energy reserves to fuel life processes • Alpha glucose, a six carbon sugar (C6H12O6) is the immediate energy source to cells • Composed of the elements C, H and O in a 1:2:1 ratio. Empirical formula is (CH2O)n • Millions of tons produced by plants & algae every year by via photosynthesis • saccharide and the suffix ose refer to sugar. i.e. glucose or monosaccharide.
Types of Carbohydrates • Monosaccharides • Oligosaccharides Contain 2 or 3 monosaccharide units • Polysaccharides Contain many monosaccharide units
Monosaccharides • Carbohydrate monomers are called monosaccharides. • distinguished by the carbonyl group they posses and the number of atoms in their carbon backbone. • carbonyl groups: aldehyde or ketone aldehyde ketone
…Monosaccharides • Distinguished by the number of atoms in their carbon backbone. • Three carbons = Triose • Four carbons = Tetrose • Five carbons = Pentose • Six carbons = Hexose
aldehyde ketone
…Monosaccharides • The two simplest monosaccharides are… • dihydroxyacetone (a triose with a ketone group) and… • glyceraldehyde (a triose with an aldehyde group)
…Monosaccharides • Aldoses are monosaccharides with an aldehyde group and many hydroxyl (-OH) groups. • Ketoses are monosaccharides with a ketone group and many hydroxyl (-OH) groups.
Learning Check Identify each as tetrose, pentose or hexose, and as aldose or ketose A B
Solution to Learning Check A B aldose, hexose ketose, pentose
…Monosaccharides:linear vs. ring structures • Monosaccharides with five or more carbons are linear molecules in the dry state, but readily form ring structures when dissolved in water.
…Monosaccharides: linear vs. ring structures • When glucose dissolves in water, the hydroxyl group on carbon 5 reacts with the aldehyde group at carbon 1 to form a closed, six-membered ring. • When this occurs, there is a 50% chance that the hydroxyl group at carbon 1 will end up below the plane of the ring. • Glucose with hydroxyl group below ring α-glucose (α = alpha). • Glucose with hydroxyl group above ring β-glucose is formed (β = Beta).
Learning Check Is this α-glucose or β-Glucose?
Solution to Learning Check α-glucose! Hydroxyl group is below plane of molecule
Oligosaccharides • sugars containing two or three simple sugars attached to one another by covalent bonds called glycosidic linkages. • Oligosaccharides include disaccharides, a sugar made of two monosaccharides. • Some disaccharides include.. • Sucrose glucose + fructose • Lactose glucose + galactose • Maltose glucose + glucose • these monosaccharides are monomers
Glycosidic linkages • Glycosidic linkages are bonds formed by condensation reactions, in which the H atom comes from a hydroxyl group on one sugar and the –OH group comes from a hydroxyl group on the other. Both the examples below are 1,4 glycosidic linkages because the bond occurs between the 1st and 4th carbons.
Polysaccharides • AKA complex carbohydrates • Several hundred to several thousand monosaccharide subunits held together by glycosidic linkages. • Some are chains, some are branched
…Polysaccharides • Amylose is an unbranched α-glucose polymer held together by α-glucose 1,4 glycosidic linkages • Amylopectin is a branched α-glucose polymer composed of a main chain with glucose molecules attached by α 1–4 glycosidic bonds and branch points formed by α 1–6 glycosidic linkages
… Polysaccharides • Starch is a polysaccharide made of 20% amylose and 80% amylopectin by mass. • Plants produce more carbohydrates than they need. They use enzymes to link excess glucose molecules and store it as insoluble starch granules.
… Polysaccharides • Humans and other heterotrophs break down starch into glucose and use it for energy in cellular respiration. • A small amount of the glucose can be converted to glycogen, another polysaccharide, and stored in the liver and muscles. • Glycogen is similar to amylopectin but it has more branches.
… Polysaccharides • Cellulose is a straight chain polymer of β-glucose held together by β 1–4 glycosidic linkages. • Hydroxyl groups at the 1 and 4 positions in β-glucose cause every other monomer to be inverted for the glycosidic linkage to form.
Learning Check • Why is every other monomer inverted in cellulose?
Solution to Learning Check • Cellulose is formed using β-glucose, where the hydroxyl group on the 1stcarbon is ABOVE the plane of the molecule. • Compare β-glucose and α-glucose…everyother β-glucose is flipped so the hydroxyls on the 1st and fourth carbon match up.
… Polysaccharides • Cellulose has a straight shape. This allows hydrogen bonds to form between the hydroxyl groups of parallel molecules. Why does this make cellulose suitable for cell walls?
Galactose D-galactose
Cyclic Structures • Monosaccharides with 5-6 carbon atoms form cyclic structures • The hydroxyl group on C-5 reacts with the aldehyde group or ketone group
Haworth Structure for D-Isomers The cyclic structure of a D-isomer has the final CH2OH group located above the ring.
Haworth Structure for D-Glucose • Write –OH groups on the right (C2, C4) up • Write –OH groups on the left (C3) down • The new –OH on C1 has two possibilites: down for anomer, up for anomer
Haworth Structure for D-Glucose -D-Glucose-D-Glucose
Learning Check 3 Write the cyclic form of -D-galactose
Solution C3 -D-galactose
JFF(Just for fun) Track your diet for the day. Roughly how much was represented by “carbs”? Surprising…..isn’t it??
