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49 Cards in this Set

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What 4 types of molecules is UDP-Glucose a precursor for?
lactose, glycoproteins, glycolipids, and proteoglycans
Do proteins attach just anywhere on carbs?
no, there is specificity
What mediates the rxn that places an AA to a carb?
Glycosyltransferase (GTF)
Where does a GTF start in adding an AA to a carb?
transfers a UDP-glucose to a -OH or amide group of an AA forming a glycosidic bond
Describe a glycoprotein.
short unbranched chains of carbs coming off a large protein
Describe glycogenin
large tree-like branching of carbs coming from a tiny protein
What is the significance of the branching.
cell surface recognition
What are oligosaccharides composed of?
glucose, galactose and their dirivatives
In terms of solubility, why is it useful to add carbs to a protein?
it can convert a hydrophobic molecule and make it hydrophilic
Where are glycoproteins found?
mucus, blood, cellular compartments, lysosomes, ECM
Where does the glycoprotein face that is attached to the cell membrane?
to the ECM
What do Proteoglycans consist of?
a core protein covalently attached to long LINEAR chains of glycosoaminoglycans (GAGs) that have a particular structure of repeating disaccharide units. (mostly carbs)
What type of charge do sugars in PGs, which are important to mediating its properties?
negative carboxylate or sulfate group
why do you need UDP-glucose for the synthesis of PGs and GP?
the high energy activated sugar drives the rxn
How do GAGs look?
long, unbranched and repeating disaccharides
Why are GAGs and PGs modified with acetylation or sulfation?
the negative charge makes them hydrophilic… this often serves an osmotic role (blood, ECM)
What is PAPS?
the activated precursor that donates the sulfate to the GAG chain
Describe the attachment of GAGs to proteins and its components
a) it is attached to a serine, threonine, or asparagine… followed by b) xylose… c) 2 each of galactose… d) repeating disaccharides
Is a template needed for the production of GAGs?
What happens after the production of the GAG?
Which has a bottle-brush appearance, GP or PG?
Which, in the absence of the carbs has a globular appearance, GP or PG?
Is chondroitin (sulfate) a PG or GP and where do you find it?
PG… cartilage, cornea,
In cartilage, collagen provides strength, what do the PGs provide?
Do GAGs require a template?
What are the precursor sugars in GAG synthesis?
What do glycosyl transferases need to recognize?
both the sugar and the protein in GAG production
In GAG degradation, do glycosyl hydrolases have specificity?
relatively low
Where are GAG degraded?
What sequentially degrades the carbohydrate in the GAG?
deacetylases and sufatases
Which enzymes degrade GAGS from the ends?
Which enzymes degrade intermediate segments of a GAG?
Describe the physical characteristics of GP.
a) shorter oligosaccharides than PG… b) oligosaccharides are branched and are not repeating…
What 3 physiological functions do GP serve?
a) hormones, Ab, enzymes, ECM structures… b) Collagen (contain galactosyl units attached to lysine residues)… c) secretions of mucus producing cells, e.g., salivary mucin
Can GPs like PGs be modified to become hydrophilic?
Where can carbs attach to proteins?
a) N-linkage to asparagine (when it is in a sequence that contains serine or threonine)… b) O-linkage to serine or threonine… c)
What is a dolichol phosphate? And where is it?
it is a substrate for the synthesis of large branched oligosaccharides… on the ER surface
Where is the phosphate terminus of a dolichol phosphate located on the ER
Facing the cytosol
Where will the linked carb chain be transferred to the protein?
lumen of the ER or Golgi
Where does N-linked glycosylation occur?
begins in the ER and ends in the Golgi
Where does O-linked glycosylation occur?
in the Golgi
Where is the protein part of the GP made?
What happens to the carb part of the GP when precusor is complete?
it flips and immerses the carb in the lumen
Blood type, which GP determines the type?
a) N-acetyl galactosaamine = A… b) Gal=B… c) nothing = O… d) R, GlcNAc, Gal, Fuc are all common
Which enzyme deficiency causes Tay-Sachs?
hexoaminidase (a glycosidase)
What is the chromosomal defect in Tay-Sachs?
insertion in exon 11 of the the ∂-chain of the hhexosaminidase A gene
Why is activity lost in Tay-Sachs?
it a four base insertion that causes a frame shift mutation
Is there a detrimental effect to those who are heterozygous for Tay-Sachs?
Acvtivity is sufficient
Why is Tay-Sachs so difficult to treat?
Blood-Brain barrier