Term
| What is a glycoconjugate? |
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Definition
1. One of the 4 classes of macromolecules in cells
2. A carbohydrate (includes sugars) linked to other chemical species |
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Term
| How many monosaccharides are there? How many are essential? What are the different subclasses? |
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Definition
There are 11 monosaccharide building blocks
2 are essential, 9 are non esssential
Subclasses:
Neutral - no amino group
Amino - have nitrogen (amino group)
hexoses - have 6 carbons
deoxy - no hydroxyl on carbon 4 |
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Term
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Definition
| A protein with sugars attached to them |
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Term
| What are the three attachment points for sugars to glycoproteins? |
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Definition
| Serine, Threonine, Asparagine |
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Term
| What is the attachment point for a N-glycan? |
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Definition
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Term
| What is the attachment point for an O-glycan? |
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Definition
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Term
| What sugars characterize proteoglycan chains? |
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Definition
Uronic acid containing sugars
(leads to a lot of sulfate in them) |
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Term
| What type of glycoproteins are found in the cytoplasm and what role do they play? |
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Definition
O-GlcNAc (O-N-acetylglucosamine)
They play a dynamic role in the regulation of transcription factors and gene expression (through serine and threonine) |
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Term
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Definition
| A part of the plasma membrane (Important: part of it, not separate from the membrane) where glycolipids, glycoproteins, and GPI anchored glycoproteins are attached to the membrane in an extremely high density |
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Term
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Definition
| A part of the plasma membrane (Important: part of it, not separate from the membrane) where glycolipids, glycoproteins, and GPI anchored glycoproteins are attached to the membrane in an extremely high density |
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Term
| Explain how glycosylation affects the AIDS virus |
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Definition
| The surface protein of the AIDS virus is extremely glycosylated (24 N-glycans on it). This virus uses the hosts cells machinery to drive its glycosylation. This heavy level of glycosylation acts as a shield and prevents the proteins in the virus membrane from being recognized even though they are highly antigenic |
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Term
| What type of glycan bond leads to increased rigidity and linearity in glycoproteins? |
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Definition
| Heavily glycosylated O-glycans |
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Term
| How do glycoproteins help in inflammation respones? |
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Definition
| Leukocytes have glycoproteins (Sialyl Lewis X) on their surfaces that recognize a protein called P-selectin on platelets and endothelial cells. This recognition allows binding of leukocytes to these cells during an inflammation response |
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Term
| What is the difference between glycosylation and glycation? |
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Definition
Glycosylation is the addition of sugars to proteins driven by an enzyme
Glycation is the non-enzymatic addition of sugars to proteins |
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Term
| Explain the stepwise process of sugar transfer onto a protein |
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Definition
1. Sugars are bound to nucleotide donors
2. Glycosyltransferases move sugars from these donors |
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Term
| What do glycosidases do? How does their role differ based on location? |
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Definition
Glycosidases handle the processing or removal of sugars from glycoproteins during N-glycan synthesis
In the ER and Golgi: Synthetic pathway processing and removal
In the lysosome: Degradation pathway |
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Term
| How are nucleotide-monosaccharide complexes imported and exported from the Golgi or ER? |
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Definition
| Each complex has its own unique transmembrane transporter to move them into and out of the cell |
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Term
| What is the structure common to all ABO blood type antigens? |
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Definition
| Fucose-N-acetylgalactosamine |
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Term
| Explain the processing of N-glycans in the ER and golgi |
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Definition
1. In the rough ER, a 14 sugar chain is added to an asparagine residue on a protein being synthesized
2. The N-glycan/protein is then passed into the Cis, medial and trans golgi where its original sugar (which is rich in mannose and glucose) is degraded
3. Glycosyltransferases and glycosidases add other sugars (sialic acid, galactose, fucose mostly) to the matured glycoprotein |
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Term
| How do glycoproteins destined for the lysosome differ from those going to be secreted or sent to the plasma membrane? |
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Definition
| Lysosome glycoproteins are phosphorylated via the mannose-6-phosphate pathway and have a mannose-6-Phosphate receptor that allows the lysosome to recognize them |
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Term
| Explain the quality control mechanism of the ER |
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Definition
If glycoproteins are not properly folded they do not leave the ER, they are degraded instead
Note: This is the problem with CF |
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Term
| What codon codes for addition of a sugar to a protein? |
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Definition
Asn-X-Ser/Thr
X is any amino acid other then proline |
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Term
| Describe how the synthesis of O-type glycans differs from that of N-type glycans |
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Definition
| O-type glycans are synthesized purely in the Golgi. Once a glycoprotein is passed from the ER to the golgi (Where N-glycans begin processing), their Serine and Threonine groups can have sugars added to them (in a step by stepwise manner) |
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Term
| How are GPI anchored proteins attached to glycoproteins and what can cleave them? |
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Definition
They are attached to the C-terminal amino acid of the proteins
The glycoprotein can be cleaved from the GPI anchor by phospholipase C
They are formed by the addition of pre made intermediates (similar to N-glycans) |
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Term
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Definition
| Glycolipids that are typically found in the brain |
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Term
| How are glycolipids synthesized? |
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Definition
| The addition of sugars to ceramide to make glucosylceramide or glactosylceramide, which can be further modified |
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Term
| What type of tissue are proteoglycans typically found in? |
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Definition
Extracellular matrices
Note: They are glycosaminoglycans bound to a core protein |
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Term
| Where are glycosaminoglycans made? |
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Definition
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