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11 Cards in this Set

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  • Back
Basic Structural Elements of Proteoglycans
2 forms exist (N linked (most abundant) and O linked)

branched structures w/o repeating units

carb does not cross link peptide chain


Carb can be added non – enzymatically (ie. In Diabetes)

Determine blood type; only diff b/c a and b is terminal sugar
N linked proteoglycan
All have core pentasaccharide

2 types exist; complex and mannose

Glycosylation site is sequence specific; uses Asn, and Serine and Threonine are candidates

In Golgi and ER
O linked proteoglycan
few common features

added in Golgi

N and O linkages can exist together on one protein

Only in Golgi
Synthesis of N linked Glycoproteins
Dolichol Pyrophosphate – lipid soluable carrier upon which oligosaccharides are constructed

A. Protein synthesis begins and peptide chain moves to ER

B. A branched oligosaccharide is created with a dolichol pyrophosphate attached

C. The oligosaccharide is transferred from the Dolichol to an Aspargine (ASN) residue of the growing peptide chain

D. Trimming of peptide chain occurs as it moves through ER

E. In the golgi, further trimming, or adding of monosaccharides occurs
Glycoprotein synthesis general
How you put a carb on or off is a very specific process
Each step occurs one at a time
Donor sugar has to be in the activated form
Each step has a different enzyme
Imp pts of N
The precursor oligosaccharide constructed on dolichol pyrophosphate is co-translationally transferred as a block of 14 sugars to a specific asparagine residue in the growing polypeptide chain in the ER lumen.

Some sugars are then trimmed before sending the glycoprotein to the Golgi where further trimming and/or addition of monosaccahrides occurs.
O linked glycoprotein synthesis
O-linked glycoproteins are NOT synthesized via the dolichol phosphate cycle. Their synthesis:
is post-translational
occurs in the Golgi
is catalyzed by individual glycosyl transferases
Structural Elements of GAGS and proteoglycans
Proteoglycans; aka mucans
Found in CT
PGs contain large polymers of glycosaminoglycans (GAGs) which are repeating disaccharides that are highly negative due to sulfate and carboxylate groups
Fx: tensil strength, rigidity
resilience, elasticity
substratum for cell
Huge Carbohydrate concentration
Contain a lot of water, but can be compressed (joints, eyelids..)
6 classes of GAGS; 5 attach to proteins; exception Hyoluronic Acid
Look like a bottle brush
Example = heparin
Glycosaminoglycans are long, linear polymers of repeating disaccharide units. When linked to a core protein, they form proteoglycans
Lysosomal Storage Dz
a. I-cell disease is due to a defective sorting of glycoproteins; can’t phosphorylate mannos
b. lysosomal storage diseases are due to defects in the glycosyl hydrolazes
c. Defects in the degradation of GAGs can cause lysosomal storage diseases
Antibiotics and Cell Wall syn
A. Penicillin targets Peptidoglycans which are a component of the bacterial cell wall
B. Bacitracin (can work on euk; so only topical); inhibits peptidoglycan synthesis
C. Vancomycin inhibits transfer of a sugar to the peptide in peptidoglycan synthesis