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MCAT Biochem > Carbs > Flashcards

Carbs Flashcards

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MCAT flashcards
1
Q

monosaccharides

A
  • trioses, tetroses, pentoses, and hexoses
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2
Q

carbs that contain aldehyde group as their most oxidized functional group

A

aldoses

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3
Q

carbs that contain ketone group as their most oxidized functional group

A

ketoses

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4
Q

what would a 6C sugar with an aldehyde group be called

A

aldohexose

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5
Q

simplest aldose

A

glyceraldehyde

O=CH
|
HCOH
|
CH2OH

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6
Q

The aldehyde carbon, C1, can participate in…

A
  • glycosidic linkages
  • sugars acting as substituents via this linkage are called glycosyl residues
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7
Q

simplest ketose

A

HOCH2C(=O)CH2OH

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8
Q

carbonyl carbon of ketose

A
  • C2
  • can participate in glycosidic bonds
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9
Q

D-fructose

A

know structure

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10
Q

D-glucose

A

know structure

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11
Q

D-galactose

A

know structure

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12
Q

D-mannose

A

know structure

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13
Q

number of stereoisomers w common backbone

A

2^n

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14
Q

epimers

A
  • special subtype of diastereomers that differ in configuration at exactly one chiral center
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15
Q

monosaccharides contain…

A
  • hydroxyl group nucleophile
  • carbonyl group electrophile
  • therefore aldoses can become hemiacetals and ketoses can become hemiketals
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16
Q

only cyclic molecules stable in solution due to ring strain

A

pyranose (6 membered)
furanose (5 membered)

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17
Q

mechanism of hemiacetal or hemiketal formation

A

1) nu attack of second to last hydroxyl group upon electrophilic carbonyl carbon
2) anomeric carbon becomes chiral and the oxygen is protonated

alpha and beta anomers

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18
Q

Fischer ~> Haworth

A
  • when we convert monosaccharides from straight-chain Fischer projection to Haworth projection, any group on the right in the Fischer projection will point down
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19
Q

mutarotation

A

exposing hemiacetal rings to water cause cause cycling between open and closed form

C1-C2 substituents can rotate freely, either alpha or beta anomer can be formed

unequal proportions at equilibrium bc axial position for hydroxyl groups is unfavored and not stable

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20
Q

monosaccharides contain…

A

alcohols and either aldehydes or ketones

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21
Q

hemiacetal open ring oxidation

A

when hemiacetal rings are open they can be oxidized to form aldonic acids (the CA version)

aldoses are considered reducing agents since they can be oxidized

22
Q

reducing sugar

A

any monosaccharide with a hemiacetal ring

23
Q

hemiacetal closed ring oxidation

A

yields a lactone, a cyclic ester w a carbonyl group persisting on the anomeric carbon

24
Q

which reagents can be used to detect the presence of reducing sugars?

A

Tollen’s reagent and Benedict’s reagent

25
Q

Tollen’s reagent

A

must be freshly prepared

start with AgNO3, which is mixed w NaOH to produce Ag2O

this is dissolved in ammonia to produce [Ag(NH3)2]+ which is the actual Tollen’s reagent

26
Q

Benedict’s reagent

A

aldehyde of aldose sugar is readily oxidized

indicated by red Cu2O precipitate

27
Q

to test specifically for glucose…

A

use glucose oxidase

28
Q

why do ketose sugars produce positive Tollen’s and Benedict’s tests?

A
  • although ketones cannot be oxidized directly to CAs, they can tautomerize to form aldoses under basic conditions via keto-enol shifts
  • while in aldose form they can react w Tollens or Benedict’s reagents to form carboxylic acid
29
Q

alditol

A

aldehyde group of aldol reduced to alcohol

30
Q

deoxy sugar

A

hydrogen that replaces hydroxyl group on the sugar (deoxyribose)

31
Q

phosphorylation of glucose

A

phosphate group is transferred from ATP to glucose

32
Q

esterification of glucose

A

carb reacts w pyridine and (CH3CO)2O at 0°C to form ester

33
Q

glycoside formation

A
  • hemiacetal react w alcohols to form acetals
  • the anomeric hydroxyl group is transformed into an alkoxy group yielding a mixture of alpha and beta-acetals with H2O as an LG
  • the resulting C-O bonds are called glycosidic bonds and the acetals formed are glycosides
  • react sugar w ethanol and HCl to form glycosides and H2O
34
Q

breaking a glycosidic bond…

A

requires hydrolysis

35
Q

disaccharides and polysaccharides forms as a result of…

A

glycosidic bonds between monosaccharides

36
Q

disaccharides

A
  • glycosidic linkage is nonspecific in that the anomeric carbon of a cyclic sugar can react w any hydroxyl group on any other sugar molecule
37
Q

sucrose

A

know structure

38
Q

lactose

A

know structure

39
Q

maltose

A

know structure

40
Q

polysaccharides

A

long monosaccharide chains linked together by glycosidic bonds

41
Q

a polysaccharide composed entirely of one monosaccharide…

A

homopolysaccharide

42
Q

a polymer made up of more than one type of monosaccharide…

A

heteropolysaccharide

43
Q

cellulose, starch, and glycogen…

A
  • all composed of D-glucose
  • differ in configuration about the anomeric carbon and the position of glycosidic bonds
44
Q

cellulose

A
  • main structural component of plants
  • homopolysaccharide of D-glucose
  • linked by B-1,4 glycosidic bonds
  • we do not have cellulase and therefore cannot digest cellulose
  • hence why fruits and veggies are good fiber
45
Q

starches

A
  • polysaccharides more digestible by humans
  • linked a-D-glucose monomers
  • plants predominantly store starch as amylose (a-1,4 glycosidic polymer)
  • amylopectin, begins as a-1,4 glycosidic polymer and has a-1,6 glycosidic bonded branches
46
Q

iodine starch testing

A
  • Iodine fits into the helical structure of amylose to test for starch
47
Q

B-amylase

A
  • cleaves amylose at the nonreducing end of the polymer (end w acetal) to yield maltose
48
Q

a-amylase

A
  • cleaves randomly along the chain to yield shorter polysaccharide chains, maltose, and glucose
49
Q

amylopectin is broken down by…

A
  • debranching enzymes
50
Q

glycogen

A
  • carb storage unit in animals
  • a-1,6 glycosidic bonds (1 for every 10 glucose molecules whereas amylopectin is 1 in every 25)
  • highly branched
  • branching optimizes the energy efficiency of glycogen and makes it more soluble in solution, thereby allowing more glucose to be stored in the body
  • allows enzymes that cleave glucose from glycogen like glycogen phosphorylase to work on many sites within the molecule simultaneously
51
Q

glycogen phosphorylase

A
  • cleave glucose from nonreducing end of glycogen and phosphorylating it, producing G1-P

MCAT Biochem (12 decks)

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