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43 Cards in this Set
- Front
- Back
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What is a glycoprotein?
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A protein that contains covalently linked carbohydrate (sugar) residues. Could be 1 sugar or 1000. No specific number
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What are the types of glycoproteins?
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Can be membrane proteins; water-soluble; can be found inside cells, within membranes, and in extracellular fluids
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How is a glycoprotein like a peanut M&M?
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Glycoprotein=sugary outside
Chocolate fatty layer=membrane Nut=protein |
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What is an N-linked glycoprotein?
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Tells me carbohydrates are attached to the amine of the amide side chain of Asparagine.
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What is an O-linked glycoprotein?
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Carbs are attached to the -OH chain side of a Ser or Thr. Plays a major rol in human biology, but we don't really understand it.
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How many carbs are used in mammalian glycolysis?
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9. Glucose, galactose, and mannase are the main ones. Don't worry abou the rest.
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What are some functions of glycoproteins?
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1. Cell:cell surface recognition (use of receptor. 2) Antigenicity (blood type); 3) EXM (makes cartilage spongy; gives ECM its basement membrane; 4) Mucins (mucous are highly sulfated sugars that trap water; 5) protein folding
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Where are proteins glycosylated?
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Usually in the Golgi, in cis-medial-or tran, while going through secretory pathway.
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Most proteins that go through secretory pathway are glycosylated. How does cell use the glycosylation?
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Glycoslyation are used as chemical handles for quality control and targeting protein to different cellular locations.
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Where does translation happen? Where are proteins made?
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Translation is in ribosomes in cytosol. Protein synthesis is in rER.
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How does a protein get to the ER?
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Water-soluble proteins have an ER signal sequence; it's typically a hydrophobic strecth.
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What's the SRP
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It's the signal recognition complex. It recognizes N-terminal signal sequences and transm domains and forms a complex with the ribosoms.
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What happens after the SRP comes along?
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The ribosome-bound SRP talk to the SRP-receptor on the ER membrane. The protein will enter the ER via a protein channel.
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Tell me about the tunnel in the ER.
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Once ribosome is bound to the SRP receptor, you can thread protein into the ER lumen. The ribosomes are bound to the ER b/c they are inserting protein in to the rER.
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When can the ribosome leave the ER?
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Once the C-terminus comes out, the ribosome can fall off. Otherwise it's tethered there by a nascent polypeptide.
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But lumen is hydrophilic, and the little red signal that got us there isn't. What happens to that?
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The hydrophobic signal sequence makes it through the tunnel. and then signal peptidase cleaves it, and it kind of hangs out in the channel. Protein continues to be shot into the ER lumen
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What about membrane proteins? How do they get incorporated?
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We just loop it into the membrane, and don't need to cut the signal sequence since its hydrophobic (if there is a sequence). Loops get pushed in and out pretty much
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When does N-linked glycosylation occur?
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Throughout the entire secretory pathway!
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What is process for N-linked glycosylation?
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As the peptide is being threaded into the ER lumen, OST (oligosaccharilytransferase) slaps on a 14-carb sugar on the consensus sequence.
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What does the 14-carb sugar do?
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It acts as handle to help with protein folding. But as sugar gets put on it's being trimmed (we're cutting some sugars).
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In N-linked glycosylation, what enzymes trim the original 14-carb sugar?
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Glucosidase 1 and Glucosidase 2
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What are calnexin and calreticulin? What do they do? Where do they work?
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They are chaperone proteins in the ER that are part of quality control. They will bind to the partially deglucosylated glycans to ensure that protein is folding properly. They work in the ER lumen.
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What are binding immunoglobulin protein (BiP); protein disulfide isomerase (PDI); and heat shock protein 70 (HSP70)? Where do they work?
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Protein-binding chaperones that assist in folding the N-linked glycoproteins. Also work in the ER lumen.
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So once a glycoprotein is deemed good to go, what's next?
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ER Mannosidase will remove just 1 mannose residue and the glycoprotein can make its way to the cis Golgi.
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What if a glycoprotein is deemed unfit?
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They get held back in the ER and are targeted for degradation.
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You're in the Golgi and you're targeted for the lysosome. What happens to you?
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You get doubly Pi on the outer branches. This double Pi handle tells cell that this protein is going to a lysosome.
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You're int he Golgi and you're either a secreted membrane protein or a plasma membrane protein. What happens to you?
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Golgi mannosidase will trim some mannose residues. You do NOT get Pi. Both head to the plasma membrane. Membrane proteins get stuck there and secreted proteins keep going.
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In the medial golgi, what's the major modification?
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You go from high mannose (lots of sugar) to complex (start getting some more interesting sugars added).
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Now what happens in the trans golgi?
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Glycoproteins get heterogeneous. Up until now, we've been homogeneous. You can be the same protein and get different sugars. Weird, not sure why it happens, but it does. You get branches, etc. etc.
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What does sialyltransferase do in the trans golgi?
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It adds some critical caps for the sugars that are needed for cell:cell recognition. Uses sialic acid residues. Something about transport vesicles (look up).
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Where does O-linked glycosylation happen?
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In the golgi.
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What initiates O-linked glycosylation?
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We're not sure; maybe specified by secondary or tertiary structure
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How are O-linked glycans added?
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One sugar @ a time. Different than glycotransferases, which add several.
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What's a mucin?
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A glycoprotein of mucus; heavily O-linked glycosylated and sulfated glycoproteins that form large tangled networks that trap water.
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How does the flu get into cells?
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The flu virus binds to cell surface thru hemagglutinin--these are sialic acid (remember the caps we add in trans). The virus is then internalized by endocytosis
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Once flu is in the cell, what happens?
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The viral and cell membranes fuse in endosomes. Lets virus transfer viral nucleocapsids into cytoplasm.
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But remember that the flu has feet that are REALLY sticky with sialic acid, which is how it gets in. But then how does it get OUT without just sticking to the cell?
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Neuraminidase severs sialic acid linkages on the host, and now the newly replicated virus can bud off.
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What's I-Cell disease?
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A lysosomal storage disease. Get hypotonia, thick and tight skin; restriction of join motion; bone deformities; inability to stand
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What does plasma look like for a patient with I-Cell?
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High levels of lysosomal proteins, which SHOULD be in the lysosome.
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What happened? Why aren't lysosomal proteins in the lysosomes in patients with I cell?
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Pt has a mutation that prevents double Pi of mannose in the cis golgi, so the proteins never got targeted to the lysosome in the first place.
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Blood type and glycoproteins . . . what do you know?
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Human blood type differences are just a result of which O-linked sugars are in your glycoproteins. Immune system will develop antibodies against blood groups not normall present in a person's blood
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What is CFTR?
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Cystic Fibrosis Transmembrane Regulator. Normally it's a ligand-gated anion channel.
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What is its role in cystic fibrosis?
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A common mutation in the CFTR gene that prevents proteins with reduced PKA sensitivity and functionality from reaching the cell surface. WATCH VIDEO.
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