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49 Cards in this Set
- Front
- Back
- 3rd side (hint)
What 4 types of molecules is UDP-Glucose a precursor for?
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lactose, glycoproteins, glycolipids, and proteoglycans
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None
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Do proteins attach just anywhere on carbs?
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no, there is specificity
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What mediates the rxn that places an AA to a carb?
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Glycosyltransferase (GTF)
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Where does a GTF start in adding an AA to a carb?
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transfers a UDP-glucose to a -OH or amide group of an AA forming a glycosidic bond
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Describe a glycoprotein.
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short unbranched chains of carbs coming off a large protein
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Describe glycogenin
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large tree-like branching of carbs coming from a tiny protein
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What is the significance of the branching.
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cell surface recognition
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What are oligosaccharides composed of?
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glucose, galactose and their dirivatives
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In terms of solubility, why is it useful to add carbs to a protein?
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it can convert a hydrophobic molecule and make it hydrophilic
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Where are glycoproteins found?
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mucus, blood, cellular compartments, lysosomes, ECM
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Where does the glycoprotein face that is attached to the cell membrane?
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to the ECM
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What do Proteoglycans consist of?
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a core protein covalently attached to long LINEAR chains of glycosoaminoglycans (GAGs) that have a particular structure of repeating disaccharide units. (mostly carbs)
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What type of charge do sugars in PGs, which are important to mediating its properties?
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negative carboxylate or sulfate group
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why do you need UDP-glucose for the synthesis of PGs and GP?
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the high energy activated sugar drives the rxn
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How do GAGs look?
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long, unbranched and repeating disaccharides
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Why are GAGs and PGs modified with acetylation or sulfation?
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the negative charge makes them hydrophilic… this often serves an osmotic role (blood, ECM)
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What is PAPS?
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the activated precursor that donates the sulfate to the GAG chain
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Describe the attachment of GAGs to proteins and its components
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a) it is attached to a serine, threonine, or asparagine… followed by b) xylose… c) 2 each of galactose… d) repeating disaccharides
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Is a template needed for the production of GAGs?
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no
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What happens after the production of the GAG?
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modification
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Which has a bottle-brush appearance, GP or PG?
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PG
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Which, in the absence of the carbs has a globular appearance, GP or PG?
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GP
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Is chondroitin (sulfate) a PG or GP and where do you find it?
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PG… cartilage, cornea,
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In cartilage, collagen provides strength, what do the PGs provide?
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flexibility
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Do GAGs require a template?
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no
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What are the precursor sugars in GAG synthesis?
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UDP-glucose
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What do glycosyl transferases need to recognize?
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both the sugar and the protein in GAG production
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In GAG degradation, do glycosyl hydrolases have specificity?
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relatively low
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Where are GAG degraded?
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lysosomes
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What sequentially degrades the carbohydrate in the GAG?
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deacetylases and sufatases
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Which enzymes degrade GAGS from the ends?
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exoenzymes
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Which enzymes degrade intermediate segments of a GAG?
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endoenzymes
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Describe the physical characteristics of GP.
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a) shorter oligosaccharides than PG… b) oligosaccharides are branched and are not repeating…
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What 3 physiological functions do GP serve?
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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
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Can GPs like PGs be modified to become hydrophilic?
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yes
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Where can carbs attach to proteins?
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a) N-linkage to asparagine (when it is in a sequence that contains serine or threonine)… b) O-linkage to serine or threonine… c)
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What is a dolichol phosphate? And where is it?
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it is a substrate for the synthesis of large branched oligosaccharides… on the ER surface
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Where is the phosphate terminus of a dolichol phosphate located on the ER
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Facing the cytosol
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Where will the linked carb chain be transferred to the protein?
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lumen of the ER or Golgi
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Where does N-linked glycosylation occur?
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begins in the ER and ends in the Golgi
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Where does O-linked glycosylation occur?
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in the Golgi
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Where is the protein part of the GP made?
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ER
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What happens to the carb part of the GP when precusor is complete?
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it flips and immerses the carb in the lumen
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Blood type, which GP determines the type?
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a) N-acetyl galactosaamine = A… b) Gal=B… c) nothing = O… d) R, GlcNAc, Gal, Fuc are all common
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Which enzyme deficiency causes Tay-Sachs?
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hexoaminidase (a glycosidase)
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What is the chromosomal defect in Tay-Sachs?
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insertion in exon 11 of the the ∂-chain of the hhexosaminidase A gene
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Why is activity lost in Tay-Sachs?
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it a four base insertion that causes a frame shift mutation
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Is there a detrimental effect to those who are heterozygous for Tay-Sachs?
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Acvtivity is sufficient
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Why is Tay-Sachs so difficult to treat?
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Blood-Brain barrier
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