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MCAT Biochem > Carbs > Flashcards

Carbs Flashcards

(51 cards)

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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

Study These Flashcards
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

Study These Flashcards
A

any monosaccharide with a hemiacetal ring

23
Q

hemiacetal closed ring oxidation

Study These Flashcards
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?

Study These Flashcards
A

Tollen’s reagent and Benedict’s reagent

25
Tollen’s reagent
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
Benedict’s reagent
aldehyde of aldose sugar is readily oxidized indicated by red Cu2O precipitate
27
to test specifically for glucose…
use glucose oxidase
28
why do ketose sugars produce positive Tollen’s and Benedict’s tests?
- 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
alditol
aldehyde group of aldol reduced to alcohol
30
deoxy sugar
hydrogen that replaces hydroxyl group on the sugar (deoxyribose)
31
phosphorylation of glucose
phosphate group is transferred from ATP to glucose
32
esterification of glucose
carb reacts w pyridine and (CH3CO)2O at 0°C to form ester
33
glycoside formation
- 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
breaking a glycosidic bond…
requires hydrolysis
35
disaccharides and polysaccharides forms as a result of…
glycosidic bonds between monosaccharides
36
disaccharides
- 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
sucrose
know structure
38
lactose
know structure
39
maltose
know structure
40
polysaccharides
long monosaccharide chains linked together by glycosidic bonds
41
a polysaccharide composed entirely of one monosaccharide…
homopolysaccharide
42
a polymer made up of more than one type of monosaccharide…
heteropolysaccharide
43
cellulose, starch, and glycogen…
- all composed of D-glucose - differ in configuration about the anomeric carbon and the position of glycosidic bonds
44
cellulose
- 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
starches
- 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
iodine starch testing
- Iodine fits into the helical structure of amylose to test for starch
47
B-amylase
- cleaves amylose at the nonreducing end of the polymer (end w acetal) to yield maltose
48
a-amylase
- cleaves randomly along the chain to yield shorter polysaccharide chains, maltose, and glucose
49
amylopectin is broken down by…
- debranching enzymes
50
glycogen
- 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
glycogen phosphorylase
- cleave glucose from nonreducing end of glycogen and phosphorylating it, producing G1-P

MCAT Biochem (12 decks)

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