CH350 > CH 13 > Flashcards

CH 13 Flashcards

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1
Q

What is glycobiology?

A

The study of glycan structure and function, including biosynthesis, diversity, and biological roles of carbohydrates.

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2
Q

What are the three major groups of carbohydrates?

A

Simple sugars (mono-, di-, and oligosaccharides)
Polysaccharides (homo- & heteropolymers)
Glycoconjugates (proteins/lipids with covalently attached glycans)

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3
Q

What are simple sugars and what do they do?

A

Mono-, di-, and oligosaccharides that often serve as metabolic intermediates in energy pathways.

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4
Q

What are polysaccharides and what types exist?

A

Large carbohydrate polymers that can be:
Homopolymers (cellulose, starch, glycogen)
Heteropolymers (chitin, heparan sulfate)

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5
Q

What are glycoconjugates and their roles?

A

Proteins or lipids with covalently attached glycans → essential for cell communication, signaling, immunity, and structure.

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6
Q

What symbols are used to represent monosaccharides in glycobiology?

A

CFG (Consortium for Functional Glycomics) symbols, standard colored shapes used to represent specific sugars.

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7
Q

Name common monosaccharides found in glycoconjugates.

A

Glucose, galactose, mannose, fucose, GlcNAc, GalNAc, and sialic acids (Neu5Ac).

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8
Q

What are N-linked glycans?

A

Glycan chains attached to the nitrogen of Asn residues, built on a core GlcNAc₂Man₃ structure.

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9
Q

What are O-linked glycans?

A

Glycan chains attached to the oxygen of Ser/Thr residues, initiating with GalNAc.

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10
Q

How complex can glycan chains be?

A

Highly branched or linear, with many modified monosaccharides and linkage possibilities (α or β), giving huge structural diversity.

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11
Q

What is the key structural feature of glycans?

A

Monosaccharides linked by glycosidic bonds in α or β conformations.

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12
Q

Where are glycans synthesized in eukaryotic cells?

A

ER and Golgi, using specific glycosyltransferases and nucleotide-activated sugars.

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13
Q

What makes glycans so diverse?

A

Many sugar building blocks
Many linkage positions
α/β stereochemistry
Branching patterns
Thus, glycans encode more structural information than proteins or nucleic acids alone.

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14
Q

What are lectins?

A

Highly specific, low‑affinity glycan-binding proteins used in recognition, immunity, and pathogen interactions.

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15
Q

How are glycans analyzed experimentally?

A

Chemical cleavage
Enzymatic digestion
Liquid chromatography
Mass spectrometry

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16
Q

What are human milk oligosaccharides (HMOs) derived from?

A

Lactose, via enzymatic extension into complex oligosaccharides.

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17
Q

Name two specific HMOs shown in the slideshow.

A

Lacto‑N‑tetraose (LNT)
Lacto‑N‑fucopentaose I (LNFP‑I)

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18
Q

What is the abundance of HMOs in breast milk?

A

They are the third most abundant component after lactose and lipids.

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19
Q

What is the probiotic function of HMOs?

A

Provide a growth advantage to bifidobacteria, which possess glycosidases to metabolize HMOs.

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20
Q

How do HMOs protect infants from pathogens?

A

Serve as soluble decoy receptors, preventing bacteria from binding intestinal epithelial cells.

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21
Q

What is cellulose made of?

A

Repeating disaccharide cellobiose, composed of glucose units linked by β‑1,4 glycosidic bonds.

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22
Q

Why is cellulose so strong?

A

Individual cellulose strands form extensive hydrogen bonds, creating tough fibrils that reinforce plant cell walls.

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23
Q

What is hemicellulose?

A

A branched polysaccharide composed of up to six types of sugar residues; example: xylan.

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24
Q

What is pectin?

A

A homopolymer of galacturonic acid involved in plant cell wall structure and gel formation.

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25
How do cellulose, hemicellulose, and pectin interact?
They form a hydrogen-bonded carbohydrate matrix that provides strength, rigidity, and flexibility to plant cell walls.
26
What is chitin, and where is it found?
A β‑1,4 polymer of GlcNAc (N-acetylglucosamine) found in fungal cell walls and the exoskeletons of insects, spiders, and crustaceans.
27
Why is chitin stronger than cellulose?
The acetamide group on GlcNAc enables even stronger H‑bond networks, increasing structural strength.
28
What is starch composed of?
A mixture of: Amylose (15–20%) Amylopectin (80–85%)
29
What is amylose?
A linear α‑1,4 glucose homopolymer that forms a left‑handed helix stabilized by hydrogen bonds.
30
What is amylopectin?
A branched α‑1,4 glucose polymer with α‑1,6 branches approximately every 15–30 residues.
31
What is glycogen, and how does it compare to amylopectin?
A highly branched glucose homopolymer with α‑1,6 branches every 8–12 residues, making it more compact and more branched than amylopectin.
32
Why does glycogen have so many branches?
To maximize the number of non‑reducing ends, allowing rapid mobilization of glucose during metabolic demand.
33
What protein is found at the center of glycogen granules?
Glycogenin, which initiates glycogen biosynthesis and acts as a structural core.
34
How large can a glycogen particle be?
A single granule can contain ~30,000 glucose units.
35
What are glycoconjugates?
Proteins or lipids modified with covalently attached glycan chains, crucial for recognition, signaling, and adhesion.
36
What are intrinsic glycoconjugate interactions?
Interactions occurring within the same organism, guiding immune recognition, neuronal migration, and cell signaling.
37
What are extrinsic glycoconjugate interactions?
Interactions between host and pathogens, enabling adhesion, mimicry, and infection strategies.
38
Give an example of bacterial glycan recognition.
E. coli FimH binds to glycans on uroplakin in the urinary tract, allowing bacterial adhesion.
39
Give an example of viral glycan recognition.
Viruses bind specific cell‑surface glycans to determine which cells they can infect.
40
How are N‑linked glycans attached?
Through Asn residues, starting with the sugar GlcNAc.
41
What is the core of all N‑linked glycans?
GlcNAc₂Man₃ (two N‑acetylglucosamine + three mannose).
42
How are O‑linked glycans attached?
To Ser/Thr residues, starting with GalNAc.
43
What are glycoproteins primarily involved in?
Cell–cell recognition and signaling on the cell surface.
44
How do glycan structures influence immune recognition?
They act as recognition patterns for lectins and immune receptors, determining self vs. non‑self interactions.
45
What glycan structure is the base for all ABO blood types?
The O antigen, a glycan subgroup found on red blood cell glycoproteins and glycolipids.
46
What enzyme forms the A antigen?
GTA (α‑1,3‑N‑acetylgalactosaminyltransferase), which adds GalNAc to the O antigen.
47
What enzyme forms the B antigen?
GTB (α‑1,3‑galactosyltransferase), which adds Gal to the O antigen.
48
How do GTA and GTB differ structurally?
They differ by only four amino acids; a key residue at position 266 determines sugar specificity.
49
What inheritance pattern do ABO blood groups follow?
Codominance — A and B alleles are both expressed when present.
50
What are the possible blood types of a child from an A‑type parent (GTA/–) and a B‑type parent (GTB/–)?
A, B, AB, or O — each with 25% probability.
51
Why can O‑type blood be given to any recipient?
O RBCs lack A and B antigens → universal donor for RBCs.
52
Why can AB individuals receive any packed RBC type?
They produce no anti‑A or anti‑B antibodies → universal RBC recipient.
53
Why must plasma transfusions be matched differently than RBC transfusions?
Plasma contains antibodies, not antigens; donor antibodies must be compatible with recipient RBC antigens.
54
What are proteoglycans?
Core proteins with multiple long glycosaminoglycan (GAG) chains, usually in the extracellular matrix.
55
What % carbohydrate content do proteoglycans contain?
50–60% carbohydrate.
56
What are common GAGs?
Heparan sulfate, chondroitin sulfate, dermatan sulfate, keratan sulfate.
57
What is the major function of proteoglycans?
Provide structural support, bind growth factors, regulate cell development, and maintain hydrated extracellular matrices.
58
How do proteoglycans differ from glycoproteins?
Proteoglycans = long GAGs, highly charged, mostly in ECM Glycoproteins = shorter oligosaccharides, mainly at cell surface for signaling
59
What are glycoproteins primarily used for?
Cell‑cell recognition, signaling, adhesion, and immune communication.
60
How are N‑linked glycans removed for analysis?
Using the enzyme PNGase F.
61
How are O‑linked glycans released?
By β‑elimination using NaOH + NaBH₄.
62
What analytical methods distinguish glycan size and chemistry?
Liquid chromatography (LC).
63
How does mass spectrometry aid glycan analysis?
It compares observed vs. predicted mass‑to‑charge ratios to identify glycan groups.
64
What are lectin arrays?
Surfaces containing hundreds of lectins that bind specific glycans, used to map glycan patterns with fluorescent samples.
65
What do antibody arrays detect in glycobiology?
Either specific glycoproteins or glycan groups, depending on array type.
66
What is the "biorecognition principle" behind arrays?
Specificity of binding: Lectin ↔ glycan Glycan ↔ protein/lectin Antibody ↔ glycoprotein
67
Why are lectin, glycan, and glycoprotein arrays important?
They allow high‑throughput glycan profiling, essential for studying disease, immunity, infection, and cell biology.
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