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CHE 541 > 17 - Carbohydrates > Flashcards

17 - Carbohydrates Flashcards

1
Q

What are some forms of glycans?

A

Oligosaccharides, polymers, mixed polymers, and free glycans

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2
Q

What are the functions of oligosaccharides?

A

Molecular recognition

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3
Q

What are the functions of carbohydrate polymers?

A

Structure, energy storage

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4
Q

What are the functions of carbohydrate mixed polymers?

A

Structure, information

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5
Q

What are the functions of free glycans?

A

Signaling, osmoprotection

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6
Q

What are some examples of biological walls?

A

Cellulose (plants), chitin (fungi), and peptidoglycan (bacteria)

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7
Q

What are some examples of internal molecular recognition?

A

Glycoconjugates on lymphocytes interact with P-selectin on endothelial cells to recruit them to the site of inflammation

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8
Q

What are some examples of extrinsic molecular recognition?

A

Hemagglutinin on influenza virus recognizes glycosylated receptors to allow viral entry

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9
Q

What is a glycoconjugate?

A

A glycan connected to something else (usually a protein)

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10
Q

What chemical interactions are important for carbohydrates and why?

A

H-bonds (lots of hydroxyls)

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11
Q

What are some examples of regulatory roles of glycans?

A

GlcNAc modifications can change protein function, localization, recognition, and stability

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12
Q

How do glycans participate in quality control?

A

Glycosylated nascent proteins in the ER determine folding

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13
Q

What is an aglycan?

A

Something that is not a glycan (protein, lipid, etc.)

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14
Q

What is the general structure of a monosaccharide?

A

A series of chiral hydroxymethylene units

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15
Q

What is an aldose?

A

A monosaccharide with an aldehyde carbonyl group

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16
Q

What is a ketose?

A

A monosaccharide with a ketone carbonyl group

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17
Q

If glucose has 6 carbons and an aldehyde, what is another name for glucose?

A

Aldohexose

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18
Q

How does a monosaccharide go from a linear form to a cyclic form?

A

One of the OH acts as a nucleophile, and the carbonyl acts as an electrophile to create a ring

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19
Q

What determines which hydroxyl will attack the carbonyl in the cyclization reaction?

A

Produce a stable ring (5 or 6 membered ring)

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20
Q

What is the structure of an acetal?

A

-C-(OR),(OR)

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21
Q

What is the structure of a hemiacetal?

A

-C-(OR),(OH)

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22
Q

When the cyclic glycan is formed, what functional group is formed?

A

A hemiacetal

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23
Q

What is the importance of a hemiacetal?

A

It is reactive

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24
Q

Which form of glucose is dominant in solution and why?

A

Cyclic form, because it is more stable as a ring

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25
Q

True or false: glucose only exists as a ring in solution

A

False: the linear and cyclic forms are in equilibrium

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26
Q

What is the anomeric carbon?

A

The carbon from the carbonyl

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27
Q

What is the stereochemistry of the anomeric carbon?

A

It can be either equatorial or axial (depends on nucleophilic attack)

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28
Q

What is the importance of the stereochemistry of the anomeric carbon?

A

It strongly influences structure of monosaccharides modified at this carbon, and therefore biological function

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29
Q

What is the alpha configuration of a glycan?

A

C1 and C5 have the same configuration (R/S)

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30
Q

What is the beta configuration of a glycan?

A

C1 and C5 have the different configuration (R/S)

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31
Q

For glucose, what is alpha?

A

Anomeric carbon is axial

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32
Q

For glucose, what is beta?

A

Anomeric carbon is equatorial

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33
Q

True or false: all alpha is axial, all beta is equatorial

A

False: alpha and beta are relative to the configuration of the C5 carbon

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34
Q

What does furanose look like?

A

Pentagon with an O in the ring

35
Q

What does pyranose look like?

A

Hexagon with an O in the ring

36
Q

What are epimers?

A

Monosaccharide stereoisomers (differ at one position)

37
Q

What are some examples of epimers?

A

Glucose and galactose, glucose and mannose

38
Q

What is a glycosidic bond?

A

The bond between the anomeric carbon on one monosaccharide and the hydroxyl on another

39
Q

What is the importance of the glycosidic bond?

A

It is the most flexible part of the disaccharide structure

40
Q

How are glycans “read”?

A

From nonreducing end to reducing end?

41
Q

What is the reducing end of a glycan?

A

The place with the free anomeric carbon (no glycosidic bond)

42
Q

What is the nonreducing end of a glycan?

A

The place without the free anomeric carbon (glycosidic bond)

43
Q

True or false: all glycans have a reducing end

A

False: if two anomeric carbons are linked together, then there is no reducing end

44
Q

What is the same between cellulose and starch?

A

They both are composed of 1,4-glycosidic bonds

45
Q

What is different between cellulose and starch?

A

They have different stereochemistry (starch is alpha, cellulose is beta)

46
Q

What is the difference in structure between cellulose and starch?

A

Starch twists, while cellulose is in sheets

47
Q

How are glycosidic bonds different from phosphodiester or peptide bonds?

A

They have many different connectivities (regiochemistry) and configurations (stereochemistry)

48
Q

What is unique about glycan biosynthesis?

A

It is not template directed

49
Q

What determines the glycan isoform on a protein?

A

The localization and expression of glycosyltransferases

50
Q

What are the three steps of the biosynthesis of glycoconjugates?

A
  1. Activation of nucleotide sugars (in cytosol)
  2. Transport of nucleotide sugars into ER and Golgi
  3. Transfer of nucleotide sugars to an acceptor (protein, lipid, glycan, etc.)
51
Q

What is the consequence of non-template directed biosynthesis of glycans?

A

A protein can have a heterogeneous mixture of glycans

52
Q

What sugars are used for activation?P

A

UDP/GDP sugars (with the exception of CMP-Sia) (can also have lipid sugars)

53
Q

What enzyme transfers sugars to form oligosaccharides?

A

Glycosyltransferases

54
Q

What reaction do glycosyltransferases catalyze?

A

NDP-sugar donor + substrate acceptor –> NDP + sugar substrate

55
Q

Where does glycosylation occur?

A

In cytosol, ER, Golgi, mitochondria, etc.

56
Q

Where are N-glycoproteins produced?

A

In the ER/Golgi

57
Q

What is the N-glycoprotein linked to?

A

An Asn residue (oligosaccharide-N-Asn-protein)

58
Q

What is the consensus sequence for N-glycosylation?

A

Asn-X-Ser/Thr (attach to Asn)

59
Q

Where are N-glycoproteins often found?

A

On the surface of secreted or membrane proteins

60
Q

How can N-glycoproteins differ?

A

By the branches of glycans present

61
Q

How do ER lectins use N-glycans?

A

They recognize the glycan to promote protein folding

62
Q

What is a lectin?

A

A protein that recognizes a glycan

63
Q

What does CRT and CNX stand for?

A

Calreticulin and calnexin

64
Q

How do CRT and CNX work?

A

They only recognize the terminal glucose in N-glycans

65
Q

What happens to CRT and CNX if there is deglucosylation?

A

The peptide is released (and hopefully folded)

66
Q

How do CRT and CNX recognize if a protein needs to be refolded?

A

If it is re-glucosylated

67
Q

What is the consensus sequence for O-glycosylation?

A

Ser/Thr - O - oligosaccharide

68
Q

What does “O-GalNAc” mean?

A

GalNAc on 1st Ser/Thr residue

69
Q

What is mucin?

A

A highly O-(GalNAc)-glycosylated protein

70
Q

What is the purpose of VNTR in mucin?

A

It is rich in Ser, Thr, and Pro, so it becomes widely O-glycosylated

71
Q

What is the function of mucin?

A

Shield against physical and chemical damage, protect against infection

72
Q

Where does O-glycosylation occur?

A

In the cytosol

73
Q

How does Chagas parasite hide from host cell immunity?

A

It has trans-sialidase enzyme to transfer Sia from host protein, and protect from recognition (avoid recognizing Gal at end of mucin)

74
Q

What is the native configuration of Chagas parasite?

A

It has Gal at the end of its mucin (can be detected by antibodies)

75
Q

Where does O-GlcNAc occur?

A

In cytosol, nucleus, and mitochondria

76
Q

What are some properties of O-GlcNAc signaling?

A

It is reversible, highly dynamic, and competes with other processes

77
Q

How is O-GlcNAc a metabolic sensor?

A
  1. UD for nucleotide metabolism
  2. P for overall energy
  3. Glc for glucose metabolism
  4. N for nitrogen metabolism
  5. Ac for fatty acid metabolism
78
Q

How does O-GlcNAc change the rate of glycolysis?

A

As O-GlcNAc increases, the rate of glycolysis decreases

79
Q

How does O-GlcNAc regulate glycolysis?

A

By decreasing activity of PFK

80
Q

How does O-GlcNAc regulate PFK?

A

It competes for binding for the product FBP at the same binding site (Ser529)

81
Q

How does cancer alter glycosylation?

A
  1. Altered branching of N-glycans
  2. Higher expression of O-linked glycans
  3. Higher surface Sia (malignancy, reduced attachment)
82
Q

How does Tamiflu work?

A

It mimics H-bond interacts to fight the flu

83
Q

What does Tamiflu do?

A

It competes with host sialic acid that the virus needs to release new particles

84
Q

Where is hyaluronic acid found?

A

In the ECM

CHE 541 (20 decks)

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