Functions Of Secreted Glycoproteins Flashcards
T or F: most extracellular Proteins are Glycoproteins
True
What are N-linked sugars attached to?
Asparagine (N)
What are O-linked sugars attached to?
Serine, Threonine, Hydroxylysine
T or F: Cells that are present in the wrong places in the body will likely die
True, e.g. liver cells can’t live in the skin
- This is due to lack of the appropriate receptors on the liver cell to get the stuff it needs from the environment
How does ebola initiate interactions with endothelial cells?
- Why not other cells?
- How does proliferation continue?
- Finds a coat glycoprotein on endothelial Cells
- Cell becomes infected and dies (Hemorrage)
- Soluble Glycoprotein blocks early general assault and inflammation (blocks neutrophils)
What is the difference between a glycoprotein and a proteoglycan?
**Note: that proteoglycans are just a subset of glycoprotein
Glycoprotein:
low amount of Carbs attached
Proteoglycan:
More sugar and GLYCOSAMINOGLYCAN chains (GAGs) are attached
What is a glycosaminoglycan (GAG)?
- Repeated polysaccharide with alternating amino sugars and acidic sugars
What is one important exception to the fact that all glycoproteins are extracellular and most extracellular proteins are glycosylated?
Albumin - abundant Serum Transport Protein
What are lectins?
Carbodydrate binding proteins for:
- cell attachment
- immune response
- lung surfactant
What glycoprotein is involved in copper binding and transport?
Ceruloplasmin
What is N-acetyl-glucosamine?
Glucose Ring Derivatized at the 2-position
T or F: Sialic acid is aka as N-Acetylneuraminate (NANA)
True
What is glycosylation?
- The process of transferring an oligosaccharide to a protein
****************************** N-linked Glycosylation: - Where does it occur? - When does it happen - How does it happen?
Where:
- Starts in Rough ER and is finished in the Golgi
When:
- AS the Polypeptide is being synthesized
How:
- Preassembled oligosaccharide is transferred to the appropriate Asparagine
What sequence gives consensus for N-linked glycosylation?
Asn-X-Ser/Thr
T or F: from yeast to man, the preassembled oligosaccharide is always the same
True
Dolichol:
- What is it?
- Bond Type?
- Predominant Sugar?
- Dolichol is a carrier of the universal pre-assembled oligosaccharide
- Linked to the Oligosaccharide via a diphosphate bond
- Mannose and Glucose are Predominant in this molecule
When can a preassembled oligosaccharide be transferred from Dolichol to another protein?
- Bonds Broken and Formed?
- Transferred to Asn-X-Ser/Thr
- Disulfate bond to Dolichol is broken, and N-glycosyl bond is formed
Where does Dolichol transfer the oligosaccharide to proteins, where is Dolichol located?
- Dolichol present in RER membrane transfers Oligosaccharide to and Asn In the RER LUMEN
If all N-glycolsylated proteins start off with the same oligosaccharide attached how do they differentiate?
- where does this occur
Remove:
- Glucoses
- Mannoses
Add:
- Galactose
- Sialic Acid
- Fructose
**Occurs as the protein passes from the ER to the Golgi
T or F: O-linked glycosylation occurs one sugar at a time
True
What adds glycosyl groups in O-linked glycosylation?
- substrate for these enzymes?
- Glycosyl Transferases Used
- Sugar Nucleotide (e.g. UDP-Gal) are used
What is the job of fibronectin?
- Binds Both Cells and Extracellular Matrix Molecules (e.g. Collagen)
What does the structure of fibronectin consist of?
- Dimer (2 similar subunits)
- Joined by Disulfide Bond at C-terminal
