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MTC Exam 2 > Glycoproteins and Proteoglycans > Flashcards

Glycoproteins and Proteoglycans Flashcards

1
Q

What is a complex carbohydrate?

A

covalent complexes of - sugars and proteins (proteoglycans and glycoproteins) - sugars and lipids (glycolipids)

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2
Q

What is a glycosaminoglycan?

A

polymers of (-) charged disaccharide repeat units - heparin and heparan-SO4 - hyaluronic acid - bunch of others too

One sugar almost always an amino sugar (hence – glycosaminoglycan), but amino group is acetylated, so no (+) charge

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3
Q

Define proteoglycan

A

proteins with lots of GAG chains hooked onto them - usually complexed with a long hyaluronic acid chain (a GAG itself) - almost all CH2O; not much protein

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4
Q

Define glycoproteins

A

proteins with some oligosaccharide chains attached - mostly protein; not too much CH2O (sometimes quite a bit, though)

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5
Q

Do glycosaminoglycan repeat units have positive, negative or no charge on their outer groups (SO4 and COO)?

A

Negative charges

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6
Q

Describe a proteglycan structure

A

Remember this has a core protein that has glycosaminoglycans attached to it (the brittles on the brush)

Many (-) charged GAG chains (e.g., keratin-SO4 or chondroitin-SO4) linked to a core protein to give a proteoglycan monomer
Negative charges repel – fuzzy “bottle-brush” molecular structure
Many proteoglycan monomers associated with long hyaluronic acid chain to form “proteoglycan aggregates

Looks like this because of all of the negative charges.

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7
Q

State the 5 Proteoglycan/GAG properties and functions.

A

Negative charges of GAG chains repel; extended in solution
slippery/slimy – high viscosity; good lubricant (mucus, joints, &c) (GAGs aka mucopolysaccharides)

resilient - associated water squishes out when compressed, but springs back when decompressed, due to (-) charge repulsion - low compressibility – “shock absorber” - good for synovial fluid in joints, vitreous humor of eye

Mostly on cell surface and extracellular matrix - especially around connective tissues (cartilage, tendon, skin, vessel walls, &c) - lots in bone matrix too - provides structural integrity to cells

Heparin is an anticoagulant – different function from other GAGs - stored in granules in mast cells that line arterial walls - released during injury; prevents runaway clotting?

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8
Q

What do you know about turnover of membrane components?

A

All membrane componentsof all cells(extracellular stuff too)undergo metabolic turnover
Half-life varies widely(minutes – months)
Constantly being replaced,then degraded

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9
Q

Define glycoprotein

A

Protein with oligosaccharide chains attached - mostly protein, a little CH2O - N-terminal aa signal sequence directs nascent GP to ER/Golgi - sugars added in ER and Golgi

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10
Q

Define O-linked glycoproteins

A

CH2O (sugar) chains hooked onto –OH (alcohol group) of Ser, Thr - blood group antigens are best example

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11
Q

Define N-linked glycoproteins

A

CH2O chains hooked onto -NH2 of Asn - most glycoproteins - nature of CH2O chains are molecular zip codes

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12
Q

If sugar chains have high mannose chain what happens to them?

A

mannose-P targets to lysosomes phosphotransferase enzyme and mannose-P receptor involved

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13
Q

If the sugar doesnt have a mannose chains but complex chains what happens to it? Where is it targeted?

A

Targeted to cell surface or extracellular space no mannose-P = outside cell

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14
Q

Give seven functions of glycoproteins

A
  1. CH2O chains are zip codes that target glycoproteins to: - lysosomes (mannose-P/mannose-P receptor required) - plasma membrane or secreted GP (complex CH2O chains)
  2. Half-lives of circulating proteins - removal of sialic acid residue = time to go (liver removes)
  3. Cell surface recognition (lots of different ways) - cell-cell interactions - cell adhesion - contact inhibition (loss = uncontrolled growth – cancers)
  4. Self vs non-self recognition – immune response (later courses)
  5. Blood group antigens (mostly glycolipids on RBC)
  6. Host-pathogen interactions – bacteria, viruses, parasites oftenuse cell-surface GP as binding/entry sites (later courses)
  7. Extracellular matrix and mucins (GI and UG tract lubricants)
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15
Q

Describe the structure of glycosphingolipids/glycolipids/sphingolipids

A

Structures and properties are generally similar to phospholipids (amphipathic)

Consist of long chain hydrophobic fatty acid and long chain amino alcohol called sphingosine with polar head consisting of water soluble sugars. Amphipathic and like to be in membranes.

Note: Lots in nervous system (neurons and myelin), but elsewhere too

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16
Q

What are some diseases associated with glycosphingolipids?

A

Sphingolipidoses - genetic defects in catabolism (lysosomal storage disorders)

Mental retardation often present; usually early death

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17
Q

Just be aware of different types of sphingoplipids

A

Base molecule is sphingosine tail + fatty acid tail. What is attached to O determines what type of sphingolipid it is.

1) if X = H, the molecule is ceramide
2) if X = P -choline, the molecule is sphingomyelin
3) if X = galactose, the molecule is cerebroside (galactosyl-ceramide, an important myelin lipid)
4) if X = galactose-sulfate, the molecule is sulfatide (also a myelin component)
5) if X = glucose, the molecule is glucosyl-ceramide (precursor to gangliosides, globosides)

18
Q

If structure/properties similar to phospholipids, why bother?

A

Who knows? Prefix “sphingo” selected due to “Sphinx-like” properties of these enigmatic lipids

19
Q

Provide 4 functions of sphingolipids

A

1) Structural components of membranes (esp. in nervous system)
2) Different (just a little) from PL – specialized membrane domains – “lipid rafts” (specialized functions)
3) Sources of smaller lipid signaling molecules – “2nd messengers” - modulate activity of protein kinases/phosphatases via signal-transduction cascades (some involved in cell growth and differentiation)
4) Sphingolipid-derived ceramide may initiate apoptosis (programmed cell death) in some cell types

20
Q

What does catabolism involve?

A

Catabolism involves: - internalization of membrane by endocytosis - transfer to lysosomes - hydrolytic degradation by catabolic enzymes

21
Q

Finish this sentence: “Like other membrane components (and extracellular GAGs) sphingolipids are:”

A
  • synthesized and inserted in nascent membrane
  • do their business
  • degraded (metabolic turnover)
22
Q

What is an “Inborn errors of metabolism”?

A

– genetic mutations in enzymes or in “activator proteins”

23
Q

What happens with lipid upstream accumulates?

A

Pathology.

  • altered cell function and/or “choked to death” - accumulation of phagocytes, which choke - normally minor degradative pathways may produce toxic effects

Note: Same is true for extracellular GAGs and surface glycoproteins

24
Q

During inborn errors of sphingolipid metabolism cell and/or function affected depends on:

A
  • localization of accumulating lipid
  • prominence of lipid
  • turnover rate
  • physiological effects of accumulating lipid (sometimes)
25
Q 
KNOW the disease and accumulating lipid for:
Krabbe
MLD
Tay-Sachs
Niemann-Pick A&B
A

Krabbe= cerebroside and psychosine
MLD=sulfatide
Tay-Sachs=ganglioside
Niemann-Pick A&B= sphingomyelin

Individually these diseases are rare but collectively are a clinical concern in pediatrics.

26
Q

Step 1 Question: Krabbe Disease is due to what?

A

Defect in B-galactosidase

27
Q

Step 1 Question: What causes metachromatic leukodystrophy?

A

Defect in arylsulfatase a

28
Q

When you have a disruption of metabolic turnover/degredation of cerebroside and sulfatide what happens?

A

Destruction of CNS myelin

29
Q

During normal catabolism of cerebroside what happens?

A

Galactose is cut off of O by B-galactosidase on the sphingolipid and you end up with ceramide + galactose.

30
Q

What happens when there is a genetic defect in beta galactosidase?

A

Normal catabolism is blocked and catabolism occurs via an alternate pathway in which the fatty acid is cut off forming psychosine (galactose + spingosine…remember fa was cut off) which is toxic and kills myelinating cells. Myelin will fall apart not because of the accumulation cerebroside but because of psychosine.

31
Q

Discuss the function of gangliosides

A

> 60 species - oligosaccharide heads have different sugar composition/sequences
Exclusively on cell surface, esp neurons (6% of GM lipid)
Oligosaccharide head is receptor for: glycosylated hormones toxins (e.g., cholera toxin-invovled in entry into a cell)
Also determinants of: cell-cell recognition/interactions growth and differentiation maybe carcinogenesis too

Very impt in nervous system

32
Q

Describe brief structure of gangliosides

A

It’s a sphingolipid. Cermide base with many sugars attached and on the bottom it has NANA. NANA (N-acetyl neruaminic acid) aka sialic acid defines gangliosides! GM1 is typical ganglioside.

33
Q

Give an example of a ganglioside degredation and lysosomal storage disease

A

Tay-Sachs Disease. This caused by defect in B-Hexosaminidase.

34
Q

What is the hallmark of Tay-Sachs Disease?

A

A cherry red spot in the retina. Note: Ganglioside accumulation in neuronsaround macula makes them gray and opaque.

35
Q

What is characteristic of Type O blood types?

A

No addition attached to the sphingolipid chain. No antigen attached

36
Q

What is characteristic of Type A blood types?

A

There is a N-acetylgalactose moiety stuck on the galactose on the sphingolipid chain. Has A antigen

37
Q

What is characteristic of Type B blood type?

A

Has galactose attached instead of N-acetylgalactose. Has B antigen

38
Q

What is the phenotype and antibodies for the the following:

OO
OA or AA
OB or BB
AB

A

Genotype Phenotype Antibodies
OO O anti-A; anti-B
OA* or AA A anti-B
OB* or BB B anti-A
AB AB neither

A and B are dominant; antigen made if 1 copy is present.

39
Q

Provide the structure of sphingomyelin, the location and a disease associated with sphingomyelin.

A

Sphingomyelin= sphingolipid + phospholipid

There is quite a bit in myelin

Niemann-Pick A & B: There is a defect in sphingomyelinase which inhibits the degradation of sphingomyelin to ceramide and phosphorylcholine (remember you add ceramide to phosphorylcholine to get a sphingomyelin)

40
Q

Vocabulary Review

A

Sphingosine – long-chain amino alcoholCeramide – sphingosine + fatty acid; base of sphingolipids
Lysosomal storage disorders – defects in lysosomal degradation: - undegraded molecules pile up in lysosomes and elsewhere
Cerebroside – Gal-ceramide; major myelin lipidKrabbe’s Ds – defective cerebroside catabolism; toxic psychosine piles up
Sulfatide – sulfated cerebrosideMetachromatic Leukodystrophy – defective sulfatide catabolism
Gangliosides – glycolipids with big sugar heads; sialic acid presentTay-Sachs Ds – defective catabolism of ganglioside
Sphingomyelin – ceramide-P-choline (lots in myelin)Neimann-Pick Ds – defective sphingomyelin catabolism
Mucopolysaccharidoses – defective catabolism of GAGs in lysosomes - Hunter’s and Hurler’s syndromes are 2 examples

MTC Exam 2 (10 decks)

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