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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
True or false: glucose only exists as a ring in solution
False: the linear and cyclic forms are in equilibrium
26
What is the anomeric carbon?
The carbon from the carbonyl
27
What is the stereochemistry of the anomeric carbon?
It can be either equatorial or axial (depends on nucleophilic attack)
28
What is the importance of the stereochemistry of the anomeric carbon?
It strongly influences structure of monosaccharides modified at this carbon, and therefore biological function
29
What is the alpha configuration of a glycan?
C1 and C5 have the same configuration (R/S)
30
What is the beta configuration of a glycan?
C1 and C5 have the different configuration (R/S)
31
For glucose, what is alpha?
Anomeric carbon is axial
32
For glucose, what is beta?
Anomeric carbon is equatorial
33
True or false: all alpha is axial, all beta is equatorial
False: alpha and beta are relative to the configuration of the C5 carbon
34
What does furanose look like?
Pentagon with an O in the ring
35
What does pyranose look like?
Hexagon with an O in the ring
36
What are epimers?
Monosaccharide stereoisomers (differ at one position)
37
What are some examples of epimers?
Glucose and galactose, glucose and mannose
38
What is a glycosidic bond?
The bond between the anomeric carbon on one monosaccharide and the hydroxyl on another
39
What is the importance of the glycosidic bond?
It is the most flexible part of the disaccharide structure
40
How are glycans "read"?
From nonreducing end to reducing end?
41
What is the reducing end of a glycan?
The place with the free anomeric carbon (no glycosidic bond)
42
What is the nonreducing end of a glycan?
The place without the free anomeric carbon (glycosidic bond)
43
True or false: all glycans have a reducing end
False: if two anomeric carbons are linked together, then there is no reducing end
44
What is the same between cellulose and starch?
They both are composed of 1,4-glycosidic bonds
45
What is different between cellulose and starch?
They have different stereochemistry (starch is alpha, cellulose is beta)
46
What is the difference in structure between cellulose and starch?
Starch twists, while cellulose is in sheets
47
How are glycosidic bonds different from phosphodiester or peptide bonds?
They have many different connectivities (regiochemistry) and configurations (stereochemistry)
48
What is unique about glycan biosynthesis?
It is not template directed
49
What determines the glycan isoform on a protein?
The localization and expression of glycosyltransferases
50
What are the three steps of the biosynthesis of glycoconjugates?
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
What is the consequence of non-template directed biosynthesis of glycans?
A protein can have a heterogeneous mixture of glycans
52
What sugars are used for activation?P
UDP/GDP sugars (with the exception of CMP-Sia) (can also have lipid sugars)
53
What enzyme transfers sugars to form oligosaccharides?
Glycosyltransferases
54
What reaction do glycosyltransferases catalyze?
NDP-sugar donor + substrate acceptor --> NDP + sugar substrate
55
Where does glycosylation occur?
In cytosol, ER, Golgi, mitochondria, etc.
56
Where are N-glycoproteins produced?
In the ER/Golgi
57
What is the N-glycoprotein linked to?
An Asn residue (oligosaccharide-N-Asn-protein)
58
What is the consensus sequence for N-glycosylation?
Asn-X-Ser/Thr (attach to Asn)
59
Where are N-glycoproteins often found?
On the surface of secreted or membrane proteins
60
How can N-glycoproteins differ?
By the branches of glycans present
61
How do ER lectins use N-glycans?
They recognize the glycan to promote protein folding
62
What is a lectin?
A protein that recognizes a glycan
63
What does CRT and CNX stand for?
Calreticulin and calnexin
64
How do CRT and CNX work?
They only recognize the terminal glucose in N-glycans
65
What happens to CRT and CNX if there is deglucosylation?
The peptide is released (and hopefully folded)
66
How do CRT and CNX recognize if a protein needs to be refolded?
If it is re-glucosylated
67
What is the consensus sequence for O-glycosylation?
Ser/Thr - O - oligosaccharide
68
What does "O-GalNAc" mean?
GalNAc on 1st Ser/Thr residue
69
What is mucin?
A highly O-(GalNAc)-glycosylated protein
70
What is the purpose of VNTR in mucin?
It is rich in Ser, Thr, and Pro, so it becomes widely O-glycosylated
71
What is the function of mucin?
Shield against physical and chemical damage, protect against infection
72
Where does O-glycosylation occur?
In the cytosol
73
How does Chagas parasite hide from host cell immunity?
It has trans-sialidase enzyme to transfer Sia from host protein, and protect from recognition (avoid recognizing Gal at end of mucin)
74
What is the native configuration of Chagas parasite?
It has Gal at the end of its mucin (can be detected by antibodies)
75
Where does O-GlcNAc occur?
In cytosol, nucleus, and mitochondria
76
What are some properties of O-GlcNAc signaling?
It is reversible, highly dynamic, and competes with other processes
77
How is O-GlcNAc a metabolic sensor?
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
How does O-GlcNAc change the rate of glycolysis?
As O-GlcNAc increases, the rate of glycolysis decreases
79
How does O-GlcNAc regulate glycolysis?
By decreasing activity of PFK
80
How does O-GlcNAc regulate PFK?
It competes for binding for the product FBP at the same binding site (Ser529)
81
How does cancer alter glycosylation?
1. Altered branching of N-glycans 2. Higher expression of O-linked glycans 3. Higher surface Sia (malignancy, reduced attachment)
82
How does Tamiflu work?
It mimics H-bond interacts to fight the flu
83
What does Tamiflu do?
It competes with host sialic acid that the virus needs to release new particles
84
Where is hyaluronic acid found?
In the ECM

CHE 541 (20 decks)

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