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BIOL 2421 - Cellular Biochem > 14. glycoconjugates > Flashcards

14. glycoconjugates Flashcards

1
Q

what are glycoconjugates

A

polysaccharides linked to proteins, small peptides, or lipids

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2
Q

are glycoconjugates homoglycans or heteroglycans? why

A

heteroglycans since the polysaccharides are composed of more than one type of monomer

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3
Q

list the three types of glycoconjugates important at the cell surface

A

proteoglycans, glycoproteins, glycosphingolipids

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4
Q

what is the sugar bound to in a glycoprotein

A

protein

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5
Q

what is the sugar bound to in a proteoglycan

A

protein

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6
Q

what is the sugar bound to in a glycosphingolipid

A

lipid

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7
Q

where are proteoglycans located

A

on the cell surface or in the ECM

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8
Q

what are proteoglycans

A

proteins complexed with large polysaccharides called glycosaminoglycans

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9
Q

what are glycosaminoglycans

A

unbranched heteroglycans of repeating disaccharide units

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10
Q

what are the disaccharide components of a glycosaminoglycan

A

one disaccharide in an amino sugar, the other in an uronic acid

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11
Q

list the types of amino sugars present in glycosaminoglycans

A

D-galactosamine or D-glucosamine (or their acetylated formed)

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12
Q

what are uronic acids

A

acidic sugars (a monosaccharide derivative)

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13
Q

how are uronic acids formed

A

when the C6 glucose/mannose/galactose is oxidized to a carb acid

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14
Q

describe the basic structure of a proteoglycan

A

a core protein with glycosaminoglycans attached at Ser residues. The glycosaminoglycans are joined at tetrasaccharide bridges/linkers

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15
Q

T or F: lots of glycosaminoglycans have esterified sulfate groups on their GlcN or GalN

A

true

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16
Q

what is the charge on GAGs and why

A

negative, because there are carb acids in the uronic acid (+ all the sulfate groups)

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17
Q

how do GAGs minimize repulsion of all those negative charges

A

they extend into a rodlike helix, which the carboxylate groups on alternating ends for maximum separation

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18
Q

what is the longest GAG called

A

hyaluronic acid

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19
Q

what type of sugar is hyaluronic acid

A

disaccharide

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20
Q

what are the two monomers of hyaluronic acid

A

glucuronic acid and N-acetylglucosamine

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21
Q

what is the role of hyaluronic acid

A

it forms a viscous non compressible solution to reduce friction in joints

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22
Q

T or F: proteoglycans are highly hydrated

A

true

23
Q

why are proteoglycans highly hydrated

A

they have a bunch of polar groups

24
Q

how do proteoglycans help skin

A

they confer elasticity to skin (as well as other parts)

25
Q

where are proteoglycans located

A

some are in the ECM, some are integral membrane proteins

26
Q

T or F: some proteoglycans can form aggregates to produce enormous assemblies

A

true

27
Q

describe proteoglycan aggregation

A

an aggrecan core protein has multiple glycosaminoglycans joined to Ser residues. This serves as the monomer. monomers join to the central strand of hyaluronic acid

28
Q

describe how defects in glycosaminoglycan synthesis/degradation can lead to disease

A

a defective enzyme leads to a truncated glycosaminoglycan, which produces multiple large bone spurs covered in cartilage

29
Q

what are peptidoglycans

A

heteroglycans attached to very short peptides

30
Q

describe the structure of peptidoglycans

A

composed of alternating residues of N-acetylglucosamine and N-acetylmuramic acid joined by β-(1→4) glycosidic linkages

31
Q

what organism and what part of that organism uses peptidoglycans

A

cell walls of bacterial contain extensive peptidoglycan

32
Q

describe peptidoglycan within bacterial cell walls

A

peptidoglycan polymers are highly cross linked by a transpeptidase enzyme to create huge rigid molecules that define the shape of bacterial cell walls and protect against fluctuation in osmotic pressure

33
Q

what is the role of transpeptidase enzyme in peptidoglycans

A

it’s used to cross link peptidoglycan polymers to create huge rigid molecules within bacterial cell walls

34
Q

what are gram negative bacterial

A

small amounts of peptidoglycan in between inner and outer cell membranes

35
Q

what are gram positive bacteria

A

up to 40 layers of peptidoglycan and no external cell membrane

36
Q

describe the relationship between penicillin and peptidoglycan

A

the antibiotic penicillin binds irreversibly to the transpeptidase active site and blocks peptidoglycan cross-linking

37
Q

how do glycoproteins differ from proteoglycans

A

they’re branched, smaller, and more structurally diverse

38
Q

describe the structure of glycoproteins

A

the carbohydrate is attached at its anomeric carbon through a glycosidic linkage to either the OH of Ser or Thr, or the amine nitrogen of Asn

39
Q

what are glycosphingolipids

A

membrane lipids with a sphingosine backbone and at least one monosaccharide as ahead group

40
Q

which carbon of sphingosine has the hydrocarbon chain attached to

A

C3

41
Q

describe what each carbon in sphingosine is bonded to

A

C1: head group
C2: fatty acid
C3: hydrocarbon chain

42
Q

where are glycosphingolipids commonly located

A

in the outer layer of the plasma membrane

43
Q

what is a cerebroside

A

single sugar head group with no net charge

44
Q

what is a globoside

A

a multisugar head group with no net charge

45
Q

what is a ganglioside

A

a multisugar head group with at least one sialic acid = net negative charge

46
Q

describe how blood type is determined by gangliosides

A

the ganglioside will have the same base, but can have one of three different head groups

47
Q

in regards to ganglioside structure, what is O type blood

A

just the base

48
Q

in regards to ganglioside structure, what is A type blood

A

an extra acetylgalactosamine

49
Q

in regards to ganglioside structure, what is B type blood

A

an extra galactose

50
Q

what happens when you receive blood with a different sugar head group than your own

A

it will be recognized as foreign and attacked by your immune system

51
Q

what is the role of lysosomal enzymes in gangliosides

A

they remove specific sugars one by one from gangliosides until only a ceramide molecule is left with a single H as a head group

52
Q

what happens when lysosomal proteins malfunction

A

they cannot break down glycosphingolipids, leading to many diseases (lipids accumulate in tissues)

53
Q

describe how tay-sachs disease is caused

A

caused by a malfunctioning enzyme that can no longer cleave a ganglioside called GM2. GM2 deposits accumulate in lysosomes causing blindness, paralysis, and death by 3 or 4 years old

BIOL 2421 - Cellular Biochem (21 decks)

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