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MCAT Biochem > Biochem #4 > Flashcards

Biochem #4 Flashcards

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MCAT flashcards
1
Q

carbohydrates containing 3 carbons

A

monosaccharides

trioses

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2
Q

carbohydrates containing 4 carbons

A

monosaccharides

tetroses

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3
Q

carbohydrates containing 5 carbons

A

monosaccharides

pentoses

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4
Q

carbohydrates containing 6 carbons

A

monosaccharides

hexose

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5
Q

monosaccharide carbohydrates containing aldehyde as the most oxidized group

A

aldoses

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6
Q

monosaccharide carbohydrates containing ketone as the most oxidized group

A

ketoses

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7
Q

D and L do not always means that they rotate optical light ____

A

in a certain direction

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8
Q

how to tell D vs. L

A

D has the OH on the highest numbered chiral center on the right ad L has it on the left.

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9
Q

stereoisomers

A

optical isomers: compounds that have the same chemical formula; these molecules differ from one another only in terms of the spatial arrangement of their component atoms.

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10
Q

absolute configuration

A

determined by the particular three-dimensional arrangement of the groups attached to the chiral carbon.

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11
Q

Fischer projection

A

two-dimensional drawing of stereoisomers.
o Be familiar with the following stereoisomers:
 Enantiomers: same sugars, different optical families (D and L-glucose)
 Diastereomers: two sugars that are in the same family (both are either ketoses or aldoses, and have the same number of carbons) that are not identical and are not mirror images
• Epimers: a special subtype of diastereomers that differ in configuration at exactly one chiral center (Ex: D-arabinose and D-ribose)

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12
Q

D- and L-glucose are

A

enantiomers

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13
Q

epimer

A

a special subtype of diastereomers that differ in configuration at exactly one chiral center (Ex: D-arabinose and D-ribose)

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14
Q

number of stereoisomers of a molecule with 4 chiral centers

A

16

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15
Q

hemiacetal

A

intramolecular reaction of aldose

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16
Q

hemiketal

A

intramolecular reaction of ketose

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17
Q

due to ring strain, the only cyclic molecules that are stable in solution are _______ and _____

A

 Due to ring strain, the only cyclic molecules that are stable in solution are six-membered pyranose rings or five-membered furanose rings

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18
Q

anomeric carbon

A

the name of the carbonyl carbon that becomes chiral in the process of ring formation. It is the one attacked by the hydroxyl group.

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19
Q

anomers

A

both formed from the intramolecular attack, one alpha and one beta.
• Ex: in glucose
o Alpha: -OH on C1 trans to CH2OH
o Beta: -OH on C1 cis to CH2OH

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20
Q

Hawthorn projection

A

useful method for describing the three-dimensional conformations of cyclic structures.
o FischerHawthorn: any group on the right in the Fischer projection will point down.
o Chair configuration is actually more accurate (with substituents in axial or equatorial positions to minimize steric hindrance)

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21
Q

downright, up lefting

A

for fischer to hawthorn

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22
Q

mutarotation

A

The spontaneous change in configuration about C-1, ring opening and closing.
o Occurs in water, happens more rapidly when catalyzed with an acid or bas

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23
Q

monosaccharides

A

contain alcohols and either aldehydes or ketones.

o These functional groups undergo normal functional group reactions.

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24
Q

lactone

A

when oxidation of the aldose occurs when it is in ring form.

carbonyl group on the anomeric carbon

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25
Q

describe reagents used to detect the presence of reducing sugars

A

 Tollens’ reagent: reduced to form a silvery mirror when aldehydes are present.
 Benedict’s reagent: red precipitate when aldehyde group of an aldose is readily oxidized.
 Ketose sugars can tautomerize to form aldehydes and then be reduced, giving positive tests.
• Tautomerization: the rearrangement of bonds in a compound, usually by moving a hydrogen and forming a double bond.
• This specific case, ketone group picks up a hydrogen and the double bond moves onto adjacent carbons, forming an enol (a compound with a double bond to an alcohol group)

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26
Q

Tautomerization

A

the rearrangement of bonds in a compound, usually by moving a hydrogen and forming a double bond.

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27
Q

deoxy sugar

A

contains a hydrogen that replaces a hydroxyl group on the sugar (carbohydrate found in DNA)

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28
Q

esterification of carbohydrates

A

replace all of the OH with the ester being reacted

@0C and pyridine

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29
Q

acetal formation of hemiacetal reacting with oxygen

A

only replace the anomeric OH with the alcohol being added.

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30
Q

glycosidic bond

A

involves anomeric carbons.

Glycosidic bonds are the covalent chemical bonds that link ring-shaped sugar molecules to other molecules. They form by a condensation reaction between an alcohol or amine of one molecule and the anomeric carbon of the sugar and, therefore, may be O-linked or N-linked

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31
Q

glycoside formation

A

when a hemiacetal reacts with an alcohol to form an acetal.

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32
Q

dissacharides

A

formed when glycosidic bonds are formed between hydroxyl groups on two monosaccharides.
o Linkage is named based on which carbons are involved.
o Important disaccharides include sucrose, lactose, and maltose.

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33
Q

polysaccharides

A

long chains of monosaccharides linked together by glycosidic bonds

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34
Q

what do cellulose, starch, and glycogen have in common?

A

glycogen (all composed of D-glucose). Differ in configuration about the anomeric carbon and the position of glycosidic bonds.

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35
Q

cellulose

A
  • Homo, made up of Beta-D-glucose molecules linked by B-1,4 glycosidic bonds
  • Humans cannot digest cellulose, we lack cellulase, good source of fiber.
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36
Q

starch

A

more digestible, broken down by enzymes and used as an energy source.
• Linked alpha-D-glucose monomers.
• Plants store starch as amylose, a linear glucose polymer linked via alpha-1,4 glycosidic bonds.
• Amylopectin: starts off like amylose but then has branches caused by alpha 1,6 glycosidic bonds.
• Beta and alpha amylase: cut at different points in the chain to break it down.
o Beta: cleaves amylose at the nonreducing end of the polymer.
o Alpha: cleaves randomly

37
Q

glycogen

A

carbohydrate storage unit in animals.
• Similar to amylopectin but it has more 1,6 glycosidic linkages.
• The branching optimizes it, better storage.
• Glycogen phosphorylase: functions by cleaving glucose from the nonreducing end of a glycogen branch and phosphorylating it, producing glucose 1-phosphate.

38
Q

what is the name of a 6 carbon sugar with a ketone group as its most oxidized group?
what is the name of a 5 carbon sugar with an aldehyde group as its most oxidized group?

A

ketohexose

aldopentose

39
Q

the aldehyde carbon can participate in____ linkages

A

glycosidic

40
Q

how to name D vs. L carbohydrates

A

depends on the location of the hydroxyl on the highest number chiral center carbon

  • if OH is on the right, “D”
  • if OH is on the left, “L”
41
Q

enantiomers

A

nonidentical, nonsuperimposable mirror images of each other. EVERY chiral center is different.

42
Q

how to calculate the number of stereoisomers?

A

2^n where n is the number of chiral centers

43
Q

how is the optical rotation of a sugar determined? From D and L confiugurations?

A

No, it is determined experimentally and is not compliant with the D and L configurations

44
Q

Do all D isomers have R configuration?

A

No

45
Q

+ optical rotation

A

postive rotation

46
Q
  • optical rotation
A

negative rotation

47
Q

in a fischer diagram, horizontal lines are ____, going ___ the page

A

wedges, out of

48
Q

in a fischer diagram, vertical lines are ____, going ___ the page

A

dashes, into

49
Q

the same sugars, in different optical families, are _____

A

enantiomers

50
Q

two sugars that are in the same family (both ketoses or aldoses and have the same number of Carbons), are _____

A

diastereomers

51
Q

a special subtype of diastereomers that differ in configuration at exactly one chiral center are called ____

A

epimers

52
Q

what is the enantiomer of D-gluocse?

A

L-gluocse

53
Q

how many carbons are in the more stable rings of carbohydrates?

A

5 (furanose) or 6 (pyranose)

54
Q

compare the alpha anomer and the beta anomer of gluocse?

A

alpha: the OH group on C-1 is axial and down
beta: the OH group on C-1 is equitorial and up

55
Q

any group on the _____ in a fischer projection will point down in a hawthorn projection

A

right

56
Q

during hemiacetal or hemiketal formation, the carbonyl carbon becomes ______

A

chiral

57
Q

compare chair and haworth drawings

A

chair is the diamond thing while haworth is the flat ring

58
Q

what is the name of an oxidized aldose?

A

aldonic acid

59
Q

any monosaccharide with a hemiacetal ring is considered a ____

A

reducing sugar because it can be oxidized.

60
Q

what two methods are used to detect the presence of reducing sugars?

A

Tollens’ reagent and Benedict’s reagent

61
Q

what is the actual Tollens’ reagent?

A

[Ag(NH3)2]+

62
Q

what does Tollens’ reagent do when there are aldehydes present?

A

it is reduced to form a silvery mirror

63
Q

what does Benedict’s reagent do when there are aldehydes present?

A

the aldehyde group of an aldose is oxidized which is indicated with a red precipitate (Cu2O)

64
Q

what is benedict’s reagant?

A

contains cupric Cu+2 ions.

65
Q

do ketose sugars provide positive benedict’s and tollens’ tests?

A

yes, thanks to tautomerization under basic conditions

66
Q

enol

A

double bond and an alcohol group

67
Q

what is a phosphate ester?

A

refer to ATP addition to glucose: H2C-O-PO3

68
Q

hemiacetals react with alcohols to form ____

A

acetals

69
Q

what are the names of acetals formed from hemiacetals reacting with alcohols

A

glycosides

70
Q

what is the leaving group when hemiacetals react with alcohols

A

water

71
Q

compare esterification and glycoside formation

A

esterification: hemiacetal + carboxylic acid (or derivative) and forms an ester (carbonyl with O)
glycoside: hemiacetal + alcohol and forms alkoxy group

72
Q

for metabolic purposes, does it make more sense for carbohydrates to be oxidized or reduced?

A

oxidized so that electron carriers can be reduced, these electron carriers can go on to facilitate processes such as oxidative phosphorylation

73
Q

describe sucrose

A

glucose-alpha-1,2-fructose

74
Q

describe lactose

A

galactose-beta-1,4-glucose

75
Q

describe maltose

A

glucose-alpha-1,4-glucose

76
Q

homopolysaccharide

A

a polymer made up of entirely one monosaccahride

77
Q

heteropolysaccharide

A

a polymer made up of more than one type of monosaccharide

78
Q

what can be used to detect starch?

A

iodine

79
Q

what enzyme is responsible for breaking down glycogen?

A

glycogen phosphorylase

80
Q

what are the two forms of starch we need to know and which is more soluble?

A

amylopectin and amylose
amylopectin is more branched and therefore more soluble: decreases intermolecular interactions and increases contact with environment.

81
Q

does glycogen or amylopectin have more branching?

A

glycogen

82
Q

glycogen branching consists of ____ linkages

A

alpha 1,6

83
Q

enantiomers have ______ optical activities

A

equal but opposite

84
Q

compare the chemical and physical properties of diastereomers

A

they are slightly different

85
Q

racemization

A

moving a solution toward an equal concentration of both enantiomers

86
Q

how do you form an acetal?

A

react a hemiacetal with alcohol

87
Q

beta amylase vs. alpha amylase

A

beta amylase cleavage results in maltose

alpha amylase cleavage results in maltose, polysaccharide chains and glucose (cause it cuts everywhere along the chain)

88
Q

compare cellulose and amylose linkages

A

cellulose used Beta 1,4 linkages

amylose uses alpha 1,4 linkages

89
Q

hemiacetal and hemiketal are monosaccharides in ring form but when alcohol is added they become _____ which is no longer a monosaccharide

A

acetal or ketal

MCAT Biochem (12 decks)

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