Complex Carbohydrates: Adhesion Molecules, Lysosomal Storage Diseases and Carboh
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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?
- no
- What happens after the production of the GAG?
- modification
- Which has a bottle-brush appearance, GP or PG?
- PG
- Which, in the absence of the carbs has a globular appearance, GP or PG?
- GP
- 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?
- flexibility
- Do GAGs require a template?
- no
- What are the precursor sugars in GAG synthesis?
- UDP-glucose
- 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?
- lysosomes
- What sequentially degrades the carbohydrate in the GAG?
- deacetylases and sufatases
- Which enzymes degrade GAGS from the ends?
- exoenzymes
- Which enzymes degrade intermediate segments of a GAG?
- endoenzymes
- 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?
- yes
- 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?
- ER
- 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