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MCAT - Biology > MCAT Biology Ch14: Carbohydrates > Flashcards

MCAT Biology Ch14: Carbohydrates Flashcards

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1
Q

carbohydrates are compounds that contain

A

C, H, and O in form of polyhydroxylated aldehydes or ketones, Cn(H2O)n

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2
Q

monosaccharide

A

single carbohydrate (simple sugar)

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3
Q

disaccharide

A

two sugars

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4
Q

oligosaccharides

A

short carb chain

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5
Q

polysacs

A

long carb chains

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6
Q

monosaccharide

A
  • 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
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7
Q

aldose

A

aldehyde sugar

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8
Q

ketose

A

simplest ketone sugar

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9
Q

stereochemistry of monosacs

A
  • 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
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10
Q

glyceraldehyde

A

http://upload.wikimedia.org/wikipedia/commons/a/a1/D-glyceraldehyde-2D-Fischer.png

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11
Q

tetroses

A

http://www.scientificpsychic.com/fitness/erythrose.gif

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12
Q

trioses

A

http://www.fao.org/docrep/field/003/AB470E/AB470E24.gif

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13
Q

dihydroxyacetone

A

http://upload.wikimedia.org/wikipedia/commons/2/28/Dihydroxyacetone.png

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14
Q

D-fructose

A

http://web.pdx.edu/~wamserc/CH331F97/Egifs/E2_3a.gif

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15
Q

D-glucose

A

http://www.uspto.gov/web/patents/classification/uspc536/c536s1-11-2.gif

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16
Q

D-galactose

A

http://upload.wikimedia.org/wikipedia/commons/5/58/D-galactose.png

17
Q

D-mannose

A

http://1.bp.blogspot.com/-YH0ZTmm6VX0/T5gNNDJhm2I/AAAAAAAABF4/ptwRkYrNdYw/s200/2+D-mannose.png

18
Q

ring properties

A
  • 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)
19
Q

pyranose

A
  • 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)
20
Q

furanose

A

5 membered ring formed from intramolecular reaction of hydroxyl group (Nu) and carbonyl (electrophile)

-from 5 carbon aldose or 6 carbon ketose

21
Q

anomer

A

cyclic stereoisomer that differ about new chiral carbon

22
Q

anomeric carbon

A
  • carbon that’s chiral in ring structure of sugar

- attached to two oxygen (O in ring and OH)

23
Q

alpha

A

OH is down, trans to CH2OH substituent

24
Q

beta

A

OH is up, cis to CH2OH substituent

25
Q

mutarotation

A
  • 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
26
Q

anomerization

A

forming one another or another from the straight-chain sugar

27
Q

Monosac rxns

A
  • ester formation, oxidation of monosacs, glycosidic rxn

- since OH, same rxns as simple alcohols

28
Q

Monosac rxns: ester formation

A
  • monosacs –> esters
  • using acid anhydride and a base (CH3CO)2O
  • all hydroxyls are esterified
29
Q

Monosac rxns: oxdation of monosacs

A
  • 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
30
Q

aldonic acids

A

oxidized aldoses

31
Q

reducing sugar

A
  • 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
32
Q

glycosidic rxns

A

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
33
Q

glycoside

A

result of hemiacetals + alcohols –> acetals

34
Q

glycosidic linkage

A

resulting C-O from hemiacetals + alcohols –> acetals

35
Q

disacs

A
  • 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
36
Q

polysaccharides

A
  • 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.
37
Q

cellulose

A
  • 1-4, B glycosidic bond
  • components of plants
  • not digestable by humans (fiber)
38
Q

starch

A
  • digestible by humans
  • plants store energy
  • 1,4 alpha glycosidic bonds, although occasional 1,6 alpha glycosidic bonds off chain
39
Q

glycogen

A
  • similar to starch, more 1,6 alpha glycosidic bonds (1 every 12 glu)
  • highly branched compound (dendrimer)

MCAT - Biology (16 decks)

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