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Carbohydrates - Glycosaminoglycans Flashcards

1
Q

Most mammalin cells are located in tissues where they are surrounded by a complex gel-like material, what is this name?

A

EXTRACELLULAR MATRIX (ECM).

  • It is now widely demonstrated that ECM is the substrate on which all tissue cells can adhere, migrate, proliferate and differentiate, and which also influence its survival, shape and function.
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2
Q

What are the three major classes of biomolecules of the ECM?

A
  1. The STRUCTURAL PROTEINS : collagen, elastin
  2. Some SPECIALIZED PROTEINS such as fibrillin, fibronectin and laminin
  3. HETEROPOLYSACCHARIDES : PROTEOGLYCANS
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3
Q

What are the five ECM functions?

A
  1. Binding and packing of tissues (connective tissue)
  2. It is a connector, an anchor and a support for the organs, consequently for the whole body;
  3. Transport of metabolites between capillaries and tissues;
  4. Defense against infection
  5. Repair of injury (via cell proliferation and fiber formation)
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4
Q

What are the HETEROPOLYSACCHARIDES in the organism?

A

HETEROPOLYSACCHARIDES in the organism are the GLYCOSAMINOGLYCANS (GAGs)

These molecules are long linear (UNBRANCHED) polysaccharides containing REPEATED DISACCHARIDIC UNITS

  • Are located not only in ECM, but they are also connected with the extracellular side of the plasma membrane.
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5
Q

What are the constituents of the DISACCHARIDIC UNITS?

A

The constituents of the DISACCHARIDIC UNITS are MODIFIED MONOSACCHARIDES, and these variations transform molecules IN NEGATIVELY CHARGED compounds, thus imparting HIGH VISCOSITY and, consequently, LOW COMPRESSIBILITY to ECM.

  • Moreover, these molecules are particularly suitable to constitute the lubricating fluids, for instance, those present in the joints (synovial fluid).
    At the same time, GAGs area able to provide a structural integrity to cells.
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6
Q

What does the DISACCHARIDIC UNIT contains?

A
  1. ONE AMINO SUGAR, such as :
    N-acetylgalactosamine (GalNAc) or N-acetylglucosamine (GlcNAc)
  2. ONE ACIDIC SUGAR ( uronic acid -> oxidation in C6) such as :
    GLUCURONIC ACID and/or IDURONIC ACID (deriving from the oxidation of idose, an epimer of glucose)
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7
Q

In some GLYCOSAMINOGLYCANS, the amino sugar presents one (or more) of the what?

A

In some glycosaminoglycans, the amino sugar presents one (or more) of the HYDROXYL GROUPS ESTERIFIED BY SULFATE or the amino group ACETYLATED by an ACETYL GROUP.

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8
Q

The combination of these SULFATE GROUPS with the CARBOXYLIC GROUPS of the URONIC ACID RESIDUES, provides to what?

A

The combination of these SULFATE GROUPS with the CARBOXYLIC GROUPS of the URONIC ACID RESIDUES, provides to the GLYCOSAMINOGLYCANS a very high density of NEGATIVE CHARGES.

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9
Q

What are the six physiological and clinical significance of specific GAGs?

A
  1. HYALURONIC ACID
  2. DERMATAN SULFATE
  3. CHONDROITI SULFATE
  4. HEPARIN
  5. HEPARAN SULFATE
  6. KERATAN SULFATE
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10
Q

What is the result from D-glucuronic acid + N-acetyl-D-glucosamine?

A

HYALURONIC ACID

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11
Q

What is the result from Iduronic acid + N-acetylgalactosamine-4 SULFATE?

A

DERMATAN SULFATE

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12
Q

What is the result from D-glucuronic acid + N-acetyl-D-galactosamine-4 (or 6)-SULFATE?

A

CHONDROITIN SULFATE

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13
Q

What is the result from D-iduronate-2-SULFATE + N-SULFO-glucosamine-6-SULFATE?

A

HEPARIN

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14
Q

What is the result from D-iduronate-2-SULFATE + N-acetylated-glucosamine-6-SULFATE?

A

HEPARIN SULFATE

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15
Q

What is the result from D-galactose + N-acetylglucosamine-6-SULFATE?

A

KERATAN SULFATE

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16
Q

HYALURONIC ACID is the only, among the GAGs, that does NOT CONTAIN what?

A

HYALURONIC ACID is the only, among the GAGs, that does NOT CONTAIN ANY SULFATE GROUP and is not found COVALENTLY attached to proteins.

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17
Q

What is the component of non-covalently formed complexes with proteoglycans in the ECM?

A

HYALURONIC ACID is a component of non-covalently formed complexes with proteoglycans in the ECM.

  • The glycosidic linkages are beta(1->3) INSIDE THE DISACCHARIDE, and beta(1->4) BETWEEN THE DISACCHARIDES.
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18
Q

What may consist of asmany as 25,000 disaccharidic units, with a M.W. at up to 10 to the 7times and it is the only GAG present both in animals and bacteria.

A

HYALURONIC ACID

  • It is present in :
    1) Synovial fluid
    2) Vitreous humor of the eye
    3) ECM of loose connective tissue
    4) Umbilical cord
    5) Cartilage
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19
Q

What are the HYALURONIC ACID’s 4 specific functions?

A
  1. Hyaluronic acid has very high concentration in embryonic tissues and is thought to play an important role in PERMITTING CELL MIGRATION during morphogenesis.
  2. Acts as LUBRICATOR and SHOCK ABSORBER expecially in articular joints, and has a function in wound repair.
  3. HYALURONIC ACID may be important in allowing TUMOR CELLS to migrate through the ECM.
  4. TUMOR CELLS can induce fibroblasts to synthesize greatly increased amounts of this GAG, to facilitate their own diffusion.
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20
Q

What does the heparin has?

A

Heparin has an extended helical conformation.

*CHARGE REPULSION BY THE MANY NEGATIVELY CHARGED GROUPS MAY CONTRIBUTE TO THIS CONFORMATION.

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21
Q

What is the one of the most abundant GAG, found in CARTILAGE, TENDONS, LIGAMENTS, HEART VALVES?

A

CHONDROITIN SULFATES.

literally, Chondroitin-4-sulfate & Chondroitin-6-sulfate

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22
Q

What are the repeating disaccharide in CHONDROITIN SULFATE?

A
  1. CHONDROITIN-4-SULFATE :
    D-glucuronic acid — N-acetyl-D-galactosamine-4-sulfate
  2. CHONDROITIN-6-SULFATE :
    D-glucuronic acid — N-acetyl-D-galactosamine-6-sulfate
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23
Q

HEPARIN is formed by repeated pairs of what?

A
  1. iduronate-2-sulfate

2. N-sulfo-glucosamine-6-sulfate

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24
Q

Describe 5 features of HEPARIN.

A
  1. It is an INTRACELLULAR GAG, with the highest net negative charge with respect to the other GAGs.
  2. Componentofintracellular granules of MAST CELLS lining the arteries of the lungs, liver and skin
  3. HEPARIN IS AN IMPORTANT ANTICOAGULANT.
    (It binds with factors IX and XI (of the clotting process), but its most important interaction is with plasma antithrombin III.
  4. HEPARIN is widely used in the treatment of thrombotic and thromboembolic conditions, such as deep vein thrombosis and pulmonary embolus.
  5. HEPARIN can also bind specifically to lipoprotein lipase present in capillary walls, causing a release of this enzyme into the circulation.
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25
Q

What is the ANTITHROMBIN III?

A

Antithrombin (AT, Antithrombin III, ATIII) is a small glycoprotein produced by the liver that inactivates several enzymes of the coagulation system.

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26
Q

What is thrombotic?

A

Thrombosis is the formation of a blood clot, known as a thrombus, within a blood vessel.

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27
Q

What are the three main features of HEPARIN SULFATE?

A
  1. Extracellular GAG, contains IDURONATE or GLUCOURONATE and GALACTOSAMINE, and it is higher ACETYLATED and less sulfated with respect to HEPARIN.
  2. Found in the basement membrane of the kidney, associated with type IV collagen and laminin where it plays a major role in determining the charge selectiveness of glomerular filtration.
  3. Some tumor cells have less heparan sulfate at their surfaces, and this may play a role in the lack of adhesiveness, characteristic of these cells.
28
Q

What are the two main features of DERMATAN SULFATE?

A
  1. Sclera of the eye, skin, blood vessels, heart valves.

2. Binds lipoproteins and plays a role in the develpoment of atherosclerosis.

29
Q

What is the sclera?

A

It is white outer layer of the eyeball.

30
Q

What is the glomerular filtration?

A

Glomerular filtration is the first step in making urine.

31
Q

What is the DERMATAN SULFATE’s repeating disaccharide unit?

A

The repeating disaccharide unit is

N-acetylgalactosamine-4-sulfate + Iduronic acid

32
Q

HEPARAN SULFATE is initially synthesized on where?

A

HEPARAN SULFATE is initially synthesized on a membrane-embedded core protein as a polymer of ALTERNATING residues of N-acetylglucosamine and glucoruronate.

  • Later, in segments of the polymer, glucuronate residues may be converted to the sulfated sugar iduronic acid, while N-acetylglucosamine residues may be deacetylated and/or sulfated.
33
Q

Some CELL SURFACE HEPARAN SULFATE GLYCOSAMINOGLYCANS remain covalently linked to where?

A

Some CELL SURFACE HEPARAN SULFATE GLYCOSAMINOGLYCANS remain covalently linked to core proteins embedded in the plasma membrane.

34
Q

The core protein of a SYNDECAN heparan sulfate proteoglycan includes what?

A

It includes a single TRANSMEMBRANE ALPHA-HELIX, as in the simplified diagram above.

35
Q

The core protein of a GLYPICAN heparan sulfate proteoglycan is attached to where?

A

It is attached to the outer surface of the plasma membrane via covalent linkage to A MODIFIED PHOSPHATIDYLINOSITOL LIPID.

36
Q

Why the KERATAN SULFATE is exception?

A

It is an exception because is present GALACTOSE INSTEAD OF AN ACIDIC SUGAR.

37
Q

What is the repeated disaccharide unit of KERATAN SULFATE?

A

The repeated disaccharide unit is :
D-GALACTOSE + N-ACETYL-D-GLUCOSAMINE-6-SULFATE.

  • Type I, is abundant in cornea, where is located between the collagen fibrils, associated with dermatan sulfates.
  • Type II, is present in loose connective tissue, associated with chondroitin sulfates.
38
Q

What is CORNEA?

A

The CORNEA is the transparent part of the eye that covers the front portion of the eye.

39
Q

What is LOOSE CONNECTIVE TISSUE?

A

LOOSE CONNECTIVE TISSUE is a category of connective tissue which includes areolar tissue, reticular tissue, and adipose tissue.

40
Q

GAGs (except for hyaluronic acid and heparin) in the body are linked to where and forming what?

A

GAGs in the body are linked to CORE PROTEINS forming PROTEOGLYCANS (also called MUCOPOLYSACCHARIDES).

41
Q

Mammalian cells can produce what?

A

Mammalian cells can produce 40 types of proteoglycans.

  • These molecules act as tissue organizers, and they influence various cellular activities, such as growth factor adhesion and activation.
42
Q

The basic proteoglycan unit consist of what?

A

The basic proteoglycan unit consists of a “core protein” to which glycosaminoglycans are covalently attached.

  • The GAGs extend perpendicularly from the proteic core in a brush-like structure.
43
Q

(CLASSIFICATION OF PROTEOGLYCANS)

The classification is based on what?

A

The classification is based on :

1) Monomeric (acid & amino sugars) composition
2) Degree and location of sulfatation
3) Type of glycosidic linkages
4) Chain length of the disaccharides
5) Nature of the core protein
6) Their tissue distribution
7) Their biologic functions

44
Q

What is the PROTEOGLYCAN?

A

Proteoglycans are proteins that are heavily glycosylated.

The basic proteoglycan unit consists of a “core protein” with one or more covalently attached glycosaminoglycan (GAG) chain(s).

45
Q

(PROTEOGLYCAN AGGREGATES)

Proteoglycan monomers associate with what?

A

Proteoglycan monomers associate with a central molecule of HYALURONIC ACID.

  • For instance, in the proteoglycan aggregate present in CARTILAGE, the GAGs are CHONDROITIN SULFATE and KERATAN SULFATE, linked to a core protein, in turn linked to hyaluronic acid molecule.
  • Structure it is very similar to a pipe cleaner or to a bottlebrush (used to clean bottles)
46
Q

The connection of GAGs with the protein core involves what?

A

The connection of GAGs with the protein core involves the N-alpha-acetylgalactosamine associated to the OH GROUP of SERINE or THREONINE (or also HYDROXYLYSINE) residues in the protein.

  • This is defined as O-GLYCOSIDIC BOND.
47
Q

Explain the nominating about O-glycosidic bond?

A

Glycosidic bonds of the form discussed above are known as O-glycosidic bonds, in reference to the glycosidic oxygen that links the glycoside to the aglycone or reducing end sugar.

In analogy, one also considers S-glycosidic bonds (which form thioglycosides), where the oxygen of the glycosidic bond is replaced with a sulfur atom.

In the same way, N-glycosidic bonds, have the glycosidic bond oxygen replaced with nitrogen.

Substances containing N-glycosidic bonds are also known as glycosylamines.

C-glycosyl bonds have the glycosidic oxygen replaced by a carbon; the term “C-glycoside” is considered a misnomer by IUPAC and is discouraged.

48
Q

Less frequently, the linkage of GAGs and protein core involves what?

A

Less frequently, the linkage of GAGs and protein core involves a specific TRISACCHARIDE, composed by 2 GALACTOSE RESIDUES and 1 XYLOSE RESIDUE and the O-GLYCOSIDIC BOND is between xylose and serine.

49
Q

What is the five roles of O-linked oligosaccharides?

A
  1. Recognition
  2. Interaction
  3. Enzyme Regulation
  4. Transpor
  5. Antigenic Determination (항원 결정인자)

(RIETA)

50
Q

GAGs are linked to the protein core also through what?

A

GAGs are linked to the protein core also through a N-GLYCOSIDIC BOND, through the amide nitrogen of an ASPARAGINE residue.

  • In general, the protein cores of proteoglycans are rich in THREONINE ASPARAGIN and SERINE RESIDUES, which allows the attachment of multiple GAGs.
51
Q

In PROTEOGLYCAN AGGREGATES, the association between what?

A

In PROTEOGLYCAN AGGREGATES, the association between HYALURONIC ACID and the CORE PROTEIN of each PROTEOGLYCAN, is not performed by a COVALENT BOND, but is is an IONIC LINKAGE.

52
Q

What is the AGGRECAN?

A

AGGRECAN is the main proteoglycan of articular cartilage. This molecule is important for the proper functioning of articular cartilage.

53
Q

What is ARTICULAR CARTILAGE?

A

Articular cartilage is the smooth, white tissue that covers the ends of bones where they come together to form joints.

54
Q

What does the AGGRECAN provides?

A

It provides a hydrated gelatinous structure (through its interactions with the ialuronic acid core and linking proteins (“link”) which gives cartilage resistance properties to the loads.

  • It is also crucial for morphogenesis(형태 형성) of the chondroskeleton during development.
55
Q

What is CHONDROSKELETON?

A

Chondroskeleton is a skeleton formed of hyaline cartilage; for example, that of the human embryo or of certain adult fishes such as the shark or ray.

56
Q

PEPTIDOGLYCAN of bacterial cell wall is formed by what?

A

Peptidoglycan of bacterial cell wall is formed by alternate residues of N-ACETYLMURAMIC ACID and N-ACETYLGLUCOSAMINE by glycosidic bonds beta(1->4).

  • The polysaccharidic chains are held together by PEPRIDIC BRIDGES.
  • These are different in the Gram(+) and Gram(-) bacteria.
57
Q

The lysis of bacterial cell is caused by the which enzyme?

A

The lysis of bacterial cell is caused by the enzyme LYSOZYME, which hydrolyzes the glycosidic bond, breaking the saccharidic chains.

  • Differently, the PENICILLIN and other related antibiotics, are able to block sythesis of the amino acidic crosslink of peptidoglycan chains between them, so the cell wall is more weak and it can suffer damages by osmotic lysis.
58
Q

What is the feature of GRAM-POSITIVE BACTERIA’s CELL WALL?

A

Bacteria cell wall is thicker to balance the absence of the second outer membrane.

59
Q

What is the feature of GRAM-NEGATIVE BACTERIA’s CELL WALL?

A

Bacteria cell wall is formed by 2 membranes and one layer of peptidoglycan between them.

  • This CELL WALL is composed by 3 thing.
  • EXTERNAL BILAYER
  • PEPTIDOGLYCANS
  • INTERNAL BILAYER
60
Q

In glycolipids and lipopolysaccharides, oligosaccharide chains are attached to where?

A

In glycolipids and lipopolysaccharaides, oligosaccharide chains are attached to membrane-anchored lipidic structures.

  • Plants and animals contain many types of glycolipids and glycosphingolipids.
61
Q

What is the ganglioside?

A

The GANGLIOSIDES are glycosphingolipids containing complex oligosaccharide chains with sialic acid residues.

*These lipids are important for cell-cell recognition, and some serve as receptors for the entry of bacterial toxins such as cholera toxin into mammalian cells.

62
Q

(Other glycosphingolipids)

Which contain oligosaccharide chains that serve as the BLOOD GROUP ANTIGENS?

A

The GLOBOSIDES, contain oligosaccharide chains that serve as the BLOOD GROUP ANTIGENS.

63
Q

(BLOOD GROUPS)

The distinction between blood groups (A,B, O and AB) depends on what?

A

It depends on the oligosaccharidic portion of glycolipids on the erythrocyte surface.

  • In all blood types the oligosaccharidic portion contains L-FUCOSE.
64
Q

(About blood group of each ANTIGENS)

  • In blood group ANTIGEN A :
  • In blood group ANTIGEN B :
  • In blood group ANTIGEN O :
  • In blood group ANTIGEN AB :
A
  • In blood group antigen A :
    At the non-reducing end, sugar is N-acetylgalactosamine
  • In blood group antigen B :
    At the non-reducing end, sugar is GALACTOSE
  • In blood group antigen O :
    At the non-reducing end are ABSENT BOTH TYPES of SACCHARIDES
  • In blood group antigen AB :
    At the non-reducing end are PRESENT BOTH TYPES of SACCHARIDES.
65
Q

What causes the kind of LYSOSOMAL STORAGE DISEASES?

A

The defects in the lysosomal enzymes reponsible for the metabolism of complex membrane-associated GAGs.

These specific diseases, defined MUCOPOLYSACCHARIDOSES (MPS) lead to an increase of
GAGs concentration within lysosomes of affected cells.

  • There are at least 14 known types of lysosomal storage diseases that affect GAGs catabolism, characterized by mental retardation and/or structural defects of the body.
66
Q

What are the syndromes result from MPS(MUCOPOLYSACCHARIDOSES)?

A
  1. MPS Types I
    Hurler’s syndrome results from a deficiency of alpha-L-iduronidase.
  2. MPS Type II
    Hunters sydrome is similar to Hurler’s syndrome buy the enzyme deficiency is for iduronate sulfatase and inheritance is X-linked.
  3. MPS Type III
    Sanfilipo’s syndrome is caused by a deficiency of one of four enzymes of which three are hydrolases and one is an N-acetyltransferase.
  • Other MPS Types are IV, VI and VII.
  • There is no MPS Type V.

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