N-Linked Glycosylation: Where Does it Occur?

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In summary, N-linked glycosylation occurs in the ER and is then further modified in the Golgi, while O-linked glycosylation occurs solely in the Golgi.
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Homework Statement


I'm confused about the N-linked glycosylation process...i know that the precursor is assembled on dolichol phosphate as 3 glucose, 9 mannose and 2 N-acetylglucosamine on the endoplasmic reticulum. After that, apparently it removes some glucose and after that the protein moves to the Golgi, where it removes some mannose to form a core pentasaccharide. But is it in the Golgi that other monosaccharides are added to this core or was it already added in the ER?
I would think its in the Golgi but then again I'm not sure...and also for O-linked i know that its not a preassembled unit and each sugar is added one by one, but again does this occur in the ER or golgi? (not sure, but my hunch is golgi)...

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N-linked glycosylation occurs in the lumen of the endoplasmic reticulum, where a polysaccharide precursor is assembled on dolichol phosphate. This precursor consists of 3 glucose, 9 mannose and 2 N-acetylglucosamine molecules. After this, some of the glucose molecules are removed and the protein then moves to the Golgi apparatus, where further modifications to the polysaccharide occur. In the Golgi, some of the mannose is removed to form a core pentasaccharide structure. Following this, other monosaccharides can be added in order to form a more complex glycan chain. O-linked glycosylation does not involve a preassembled unit and instead each sugar is added one by one. This process occurs in the Golgi apparatus, where sugars such as galactose, N-acetylgalactosamine, glucuronic acid, or sialic acid are added to a protein.
 

1. What is N-linked glycosylation?

N-linked glycosylation is a process in which a sugar molecule called a glycan is attached to a specific amino acid (asparagine) on a protein. This modification is important for the proper folding, stability, and function of the protein.

2. Where does N-linked glycosylation occur?

N-linked glycosylation occurs in the endoplasmic reticulum (ER) and Golgi apparatus of eukaryotic cells. These are cellular organelles involved in the production, processing, and transportation of proteins.

3. What is the purpose of N-linked glycosylation?

N-linked glycosylation serves several purposes, including protein folding and stability, cell-cell recognition and communication, and protection against degradation. It can also influence the function and localization of proteins within the cell.

4. How is N-linked glycosylation regulated?

N-linked glycosylation is regulated by a complex network of enzymes and chaperones that work together to ensure that the correct glycan is attached to the protein at the right location. Mutations in these enzymes can lead to diseases such as congenital disorders of glycosylation (CDG).

5. Can N-linked glycosylation be altered?

Yes, N-linked glycosylation can be altered by various factors, including changes in the cellular environment, mutations in the enzymes involved in the process, and certain diseases. Understanding how to manipulate N-linked glycosylation has important implications for the development of therapeutics for diseases that involve this process.

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