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Medicinal Chemistry > Carbohydrates > Flashcards

Carbohydrates Flashcards

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1
Q

the general formula of carbohydrates

A

Cn(H2O)n

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2
Q

monosaccharides

A

single monomer

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3
Q

disaccharides

A

2 covalently linked monosaccharides

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4
Q

polysaccharides

A

many-covalently linked monosaccharides by O- glycosidic bonds

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5
Q

what do monosaccharides contain

A

a carbon chain, an aldehyde/keton, and hydroxyls on each carbon atom except the carbonyl.

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6
Q

aldopentose

A

5 carbon saccharide with an aldehyde group

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7
Q

keto hexane

A

a 6-carbon saccharide with a ketone group

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8
Q

how do we establish a chiral center?

A

we resort to Fischer projections to establish the configuration of the chiral center by comparison with D- or L- glyceraldehyde

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9
Q

how do we determine if a carbohydrate is D or L?

A

based on the configuration of the chiral C furthest away from the aldehyde/ketone

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10
Q

d-glucose

A
  • known as dextrose
  • building block of the disaccharides sucrose and lactose and of polysaccharides such as cellulose and glycogen
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11
Q

d-galactose

A
  • aldohexose with the formula C6H12O6
  • obtained from lactose found in milk
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12
Q

galactosemia

A

a condition where the enzyme needed to convert D-galactose to D-glucose is missing. galactose accumulates in the blood and tissue which can lead to cataracts, mental retardation, and liver disease

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13
Q

d-fructose

A

ketohexose with the formula C6H12O6
obtained as one of the hydrolysis products of sucrose

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14
Q

d-ribose

A
  • an aldopentose with the formula C5H10O5
  • component of RNA
  • has 3 chiral centres
  • reduced form is 2 deoxy-D-ribose which is part of DNA
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15
Q

mutarotation

A

takes place in the formation of cyclic forms of monosaccharides. nucleophilic attack from the -OH causes the carbon atom to undergo a change in hybridization from sp2 to sp3.

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16
Q

anomers

A

isomers with different chirality at the carbon atom that in the open-chain form is a carbonyl

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17
Q

alpha anomer

A

the OH group is pointing down

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18
Q

beta anomer

A

the OH group is pointing up

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19
Q

mutarotation in fructose

A

makes the glycosylation in glucose and galactose possible

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20
Q

what structure do saturated 6-membered rings assume?

A

a half-chair conformation due to sp3 hybridisation

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21
Q

which form of monosaccharides can undergo oxidation?

A

open-chain

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22
Q

oxidation of monosaccharides with aldehydes

A

if there is an aldehyde group with an adjacent hydroxyl group it can be oxidised to a carboxylic acid by an oxidizing agent such as Benedicts solution

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23
Q

oxidation of monosaccharides with ketones

A

ketoses should not undergo oxidation but intermolecular arrangements make monosaccharides oxidizable.

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24
Q

reduction of monosaccharides

A

the carbonyl group can be reduced to the corresponding agents

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25
Q

reducing agents used for the reduction of monosaccharides

A

Pd + H2 or NaBH4 or enzymatically with the NADH cofactor as a hydride donor

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26
Q

describe the condensation of 2 monosaccharides to form a disaccharide

A
  1. one monosaccharide provides the hemiacetal in the form of anomeric carbon
  2. one provides a hydroxyl
  3. reaction leads to a stable acetal releasing a water molecule
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27
Q

the bond between 2 monosaccharides

A

glycosidic bond which can have a configuration of alpha or beta

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28
Q

maltose

A

has an alpha (1,4) glycosidic bond

29
Q

lactose

A

glucose + galactose
found in breastmilk
hydrolyzed by the enzyme lactase

30
Q

sucrose

A

-consists of a-D-glucose and b-D-glucose
- has an alpha-beta (1->2) glycosidic bond between C1 of glucose and C2 of fructose
cannot undergo mutarotation and cannot be oxidised

31
Q

taste receptors

A

proteins that bind to substances that depolarise the cells and transmit a taste signal through facial and cranial nerves.

32
Q

sweet receptors

A

TAS1R2 and TAS1R3 are found in the palate and the back of the tongue and any molecule that can bind to TAS1 will deliver a sensation of sweetness

33
Q

what cannot the monosaccharide providing the anomeric carbon in the condensation reaction undergo

A

mutarotation

34
Q

what is the glycosidic bond?

A

is an acetal

35
Q

hemiacetal + alcohol

A

nucleophilic substitution. the cyclic hemiacetal can react with other nucleophiles such as NH3 to yield other products

36
Q

N-glycosidic

A

bond between the nitrogenous base and the ribose

37
Q

homopolysaccharides

A

single repeating unit

38
Q

how does heterogeneity arise in homopolysaccharides?

A

from differences in monosaccharides linked together and in the pattern of glycosidic bonds: branching

39
Q

amylose

A

poly alpha 1,4 glucose
linear chains
found in plants
broken down by enzymes called alpha-amylases

40
Q

amylopectin

A

poly alpha 1,4 glucose and alpha 1,6 branches
branching occurs every 30 glucose units
amylopectin associated with amylose via non-covalent hydrogen bonding interactions to form starch

41
Q

cellulose

A

-poly beta 1,4 glucose
- strands of cellulose can establish interchain hydrogen bonds that reduce the solubility and promote the formation of a fibrillar structure
- nondigestible: animals lack the enzyme required for the hydrolysis of the beta 1,4 glycosidic bond

42
Q

glycogen

A

poly alpha 1,4 glucose with a 1,6 branching
more branching than amylopectin
branching every 8-12 residues

43
Q

why is branching important in glycogen?

A
  1. when glucose is needed, monosaccharides are detached at the non-reducing end of the chain
  2. branching offers many ends to the enzymes that catalyze the removal
  3. in a time unit, much glucose is released, and glucose increases quickly
44
Q

hemiacetal+ alcohol

A

acetal + water

45
Q

heteropolysaccharides

A

when more than one type of monosaccharide is used

46
Q

what can heteropolysaccharides function as

A
  1. structural
  2. increasing solubility of proteins
  3. shielding proteins from the immune system
  4. stabilising extracellular proteins
  5. anticoagulants
  6. blood groups
47
Q

glycans

A

polysaccharides associated with other molecules

48
Q

glycosylated proteins

A

glycans associated with proteins to yield glycosylated proteins

49
Q

n-glycosylation

A

glycans are attached to Asn residues that are found in consensus sequences -Asn-non Pro- Ser/Thr

50
Q

o-glycosylation

A

glycans are attached to Ser or Thr residues

51
Q

N-acetyl glucosamine

A

modified sugar

52
Q

which proteins undergo glycosylation?

A

extracellular proteins produced in the cell and then secreted or translocated to the cell membrane

53
Q

glycosylation

A

when a carbohydrate is covalently attached to a macromolecule such as a protein or a lipid

54
Q

Glycosaminoglycans (GAGs)

A

linear polymers of repeating disaccharides

55
Q

what is the composition and mass of GAGs determined by?

A

by the relative activities of processing enzymes

56
Q

when do mucopolysaccharides arise

A

when the activity of breakdown enyzmes is reduced

57
Q

what does a disaccharide of glycosaminoglycan consist of?

A

uronic acid (sugar with a COOH function) and an amino sugar (sugar with an amino group replacing the OH)

58
Q

how can sugars be modified?

A

by formation of sulfate esters

59
Q

where are GAGs synthesised?

A

in the golgi apparatus

60
Q

3 classes of GAGs

A

heparin/ heparan sulfate
chondroitin sulfate/dermatan sulfate
keratan sulfate

61
Q

how are GAGs linked to proteins

A

via O-glycosidic bond or N-glycosidic bond

62
Q

proteoglycans

A

heavily-glycosylated proteins with one or more GAGs attached to the core polypeptide

63
Q

cartilage composition

A

composed of collagen, GAGs and proteoglycans

64
Q

heparin GAG

A

GlcUA/ IdoUA

65
Q

keratan sulfate GAG

A

Gal neutral or sulfate

66
Q

Chondroitin sulfate GAG

A

GlcUA

67
Q

Heparan sulfate GAG

A

GlcUA or IdoUA

68
Q

Dermatan sulfate GAG

A

GlcUA or IdoUA

69
Q

Hyaluronic acid GAG

A

GlcUA

Medicinal Chemistry (10 decks)

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