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10 Cards in this Set

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Contrast Proteoglycans and Glycoproteins structure.
Proteoglycans
95+% Sugar
Alternating Acid & Amino Sugars
Trisaccharide links of oligosaccharides (Xylose - Galactose - Galactose)
Diseases are Hunter's and Hurler's (mucopolysaccharidoses)

Glycoproteins
Mainly protein
8 Sugars O-Linked or N-Linked
Diseases include Inclusion Cell Disease (glycoproteinoses)
Discuss the general composition of GAGs and the possible bottle-brush structure of proteoglycans
GAGs are long, unbranched polysaccharide chains consisting of repeating disaccharide units (amino sugar - acidic sugar alternating). They are very large with huge molecular weights.

ALL GAGs HAVE STRONG NEGATIVE CHARGES!!!
Describe the synthesis of hyaluronic acid and the extracellular assembly of proteoglycan aggregates using link proteins leading to shock absorbing aggregates
Unlike other glycosaminoglycans, Hyaluronic acid does not contain sulphur and is not linked to a protein. They are nothing but long (25k bp), unbranched disaccharide polymers. They are extruded from the cell and used as a backbone for proteoglycan aggregates.

GAGs are able to soak up huge amounts of water and these giant hydrated assemblies make up the majority of ground substance and sinovial fluid. They can shed the water allowing compression and then immediately pick it back up after. This allows them to function as shock absorbers.
Discuss the structure and function of heparin
Heparin has the highest negative charge of the GAGs. It is a natural anticoagulant, binding strongly to antithromin III.

It is made of alternating glucosamine and glucouronic or iduronic acids.

It is an extracellular component of mast cells that line arteries, especially in the liver, lungs and skin.
Outline the synthesis of O-linked glycoproteins and indicate the amino acid side chains involved
An O-glycosidic link is where OH groups on the glycoprotein bind with serine, threonine or hydroxylysine residues on the polypeptide chain. The bond is ually between an OH group and N-acetylgalactosamine, but mannose, galactose and xylose residues also occur.

The first covalent bond is made in the RER lumen with membrane-bound microsomal glycosyltransferases. Further sugars are added as the glycoprotein is elongated in the golgi.
Outline the synthesis of N-linked glycoproteins and indicate the significance of dolicol-pyrophosphate and mannose involvement.
An N-glycosidic link happens between the amide nitrogen on an asparagine residue and a sugar in two stages.

Assembly of a dolichol-linked oligosaccharide
1. Protein synthesis begins in the ER
2. A branched oligosaccharide is synthesized bound to Dolichol-prophosphate (a polyprenol lipid substrate for a glycosyltransferase.)
3. The oligosaccharide is transferred to an asparagine residue on the polypeptide.
4. The carbohydrate chain is trimmed as it moves through the ER.

N-linked glyoprotein assembly
5. Further modification is done in the golgi either as trimming and/or more addition.

Phosphorylation of specific mannosyl residues of hydrolytic glycoenzymes is a signal for golgi membrane-bound mannose 6-phosphate receptors which determine if the glycoprotein is translocated intracellularly or shipped out of the cell.
Compare the concepts of the synthesis of O-linked and N-linked glycoproteins.
Both begin in the ER and are extended in the golgi.
Both end up with the same type of product which are used for similar purposes.

O-linked
N-acetyl-galactosamine is attached to the OH of a Serine or Threonine.
There is no amino acid consensus sequence after this.
There is no other substrate needed.

N-linked
N-acetylglucosamine is attached to the amide nitrogen of an Asparagine.
Any AA but a Proline may be added next, followed by a Serine or Threonine.
Dol-P must be attached to the glycotransferase to add sugar groups.
Discuss the function of hyaluronic acid related to facilitation of cell migration.
This objective was removed by Dr. Williams.
Discuss some of the roles of glycoproteins (glycocalyx, blood proteins, mucins)
This objective was removed by Dr. Williams