Kaplan MCAT Biology Ch. 14: Carbohydrates
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sportyperson246 on June 28, 2012
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39 terms
Terms | Definitions |
|---|---|
 carbohydrates are compounds that contain | C, H, and O in form of polyhydroxylated aldehydes or ketones, Cn(H2O)n |
| monosaccharide | single carbohydrate (simple sugar) |
| disaccharide | two sugars |
| oligosaccharides | short carb chain |
| polysacs | long carb chains |
| monosaccharide | -simplest units -# of carbons they possess; num. prefix and suffix -ose (ex: triose, tetrose); begins w/ C close to carbonyl (c-1) -simplest: glyceraldehyde -polyhydroxlyated aldehyde (aldose) -simplest ketone sugar (ketose): dihydroyacetone; ketone will receive lowest possible number; ketone group C-2 on MCAT -every carbon (except carbonyl) carry -OH |
| aldose | aldehyde sugar |
| ketose | simplest ketone sugar |
| stereochemistry of monosacs | -used glyceraldehyde --> D(+)and L(-) config -all other monosacs assigned to D and L in relationship to glyceraldehyde -highest # chiral center (farthest from carbonyl) right is D and left is L -same sugars, diff. optical fam (D and L--> enantiomers -nonidentical (nonmirror image) w/in same fam (ketose/aldoses, same # C) --> diastereomers -diastereomers differ only at one chiral center --> epimers |
| glyceraldehyde | http://upload.wikimedia.org/wikipedia/commons/a/a1/D-glyceraldehyde-2D-Fischer.png |
| tetroses | http://www.scientificpsychic.com/fitness/erythrose.gif |
| trioses | http://www.fao.org/docrep/field/003/AB470E/AB470E24.gif |
| dihydroxyacetone | http://upload.wikimedia.org/wikipedia/commons/2/28/Dihydroxyacetone.png |
| D-fructose | http://web.pdx.edu/~wamserc/CH331F97/Egifs/E2_3a.gif |
| D-glucose | http://www.uspto.gov/web/patents/classification/uspc536/c536s1-11-2.gif |
| D-galactose | http://upload.wikimedia.org/wikipedia/commons/5/58/D-galactose.png |
| D-mannose | http://1.bp.blogspot.com/-YH0ZTmm6VX0/T5gNNDJhm2I/AAAAAAAABF4/ptwRkYrNdYw/s200/2+D-mannose.png |
| ring properties | -hydroxyl group (Nu) and carbonyl (electrophile) --> intramolecular rxn --> cyclic hemiacetal (from aldoses) or hemiketals (ketoses) -ring strain --> only cyclic in sol is pyranose (6) or furanose (5) -oxygen becomes member of ring -c-1 becomes chiral (anomeric carbon), compound known as anomers -when w/ water --> spon open and reform -single bond between C1 and C2 rotate freely --> alpha or beta (mutarotation) |
| pyranose | -6 membered ring formed from intramolecular Nu acyl substitution of hydroxyl group (Nu) and carbonyl (electrophile) -chairlike config, min steric hindrance -Fisher Projection --> Haworth (right --> down, left --> up) -from 6 carbon aldose or seven carbon ketose -OH is either alpha (trans) or beta (cis) |
| furanose | 5 membered ring formed from intramolecular reaction of hydroxyl group (Nu) and carbonyl (electrophile) -from 5 carbon aldose or 6 carbon ketose |
| anomer | cyclic stereoisomer that differ about new chiral carbon |
| anomeric carbon | -carbon that's chiral in ring structure of sugar -attached to two oxygen (O in ring and OH) |
| alpha | OH is down, trans to CH2OH substituent |
| beta | OH is up, cis to CH2OH substituent |
| mutarotation | -a or b config after ring exposed to water -occurs more rapidly when catalyzed w/ acid or base -mix both in eq. concentration -process of one anomer changing into the other anomer by opening and reclosing -alpha --> less favored due to OH axial --> steric strain |
| anomerization | forming one another or another from the straight-chain sugar |
| Monosac rxns | -ester formation, oxidation of monosacs, glycosidic rxn -since OH, same rxns as simple alcohols |
| Monosac rxns: ester formation | -monosacs --> esters -using acid anhydride and a base (CH3CO)2O -all hydroxyls are esterified |
| Monosac rxns: oxdation of monosacs | -switching between anomeric config, hemiacetal rings spend short period of time in open-chain aldehyde form -aldehydes can be oxidized to carb acids (oxidized aldoses called aldonic acids); reducing agents |
| aldonic acids | oxidized aldoses |
| reducing sugar | -hemiacetal ring -Tollen's (reducing Ag+ to metallic silver) and Benedict's (red ppt of Cu2O) reagent detect presence - positive -ketose also reducing sugar and is pos, but since can't be oxidized to carb acid, it isomerizes to aldoses via keto-enols shifts -more powerful oxidizing agent like dilute HNO3 w/ oxidize both aldehyde and primary alcohol to carb acid |
| glycosidic rxns | hemiacetals + alcohols --> acetals -under acidic conditions -anomeric hydroxyl group transformed into alkoxyl group --> mix of alpha and beta acetal (w/ water as LG) - glycoside -forms glycosidic linkage (C-O) -Sn2, sugar as nucleophile |
| glycoside | result of hemiacetals + alcohols --> acetals |
| glycosidic linkage | resulting C-O from hemiacetals + alcohols --> acetals |
| disacs | -two monosacs join, hydroxides act like alcohol -most common is glycosidic linkage, 1,4 linkage (a - maltose, b - cellobiose), there's also 1,6 and 1,2 -either alpha or beta, depending on orientation of OH group on anomeric carbon -often cleaved in presence aq. acid |
| polysaccharides | -large chains of monosac linked by glycosidic bonds -three most important: cellulose, starch, and glycogen (diff function, same monosac, D-glu) -diff in config about anomeric carbon and position of glycosidic bonds -- bio diff. |
| cellulose | -1-4, B glycosidic bond -components of plants -not digestable by humans (fiber) |
| starch | -digestible by humans -plants store energy -1,4 alpha glycosidic bonds, although occasional 1,6 alpha glycosidic bonds off chain |
| glycogen | -similar to starch, more 1,6 alpha glycosidic bonds (1 every 12 glu) -highly branched compound (dendrimer) |
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