Question

Indicate whether each of the following occurs in the ER (E), Cytoplasm (C), Golgi apparatus (G), lysosome (L) or mitochondria (M). Your answer would be a four-letter string composed of letters E, C, G, L and Monly (e.g. ECEM, please do not use spaces). You may choose the same letter twice or not choose it at all. This is an all or none questions, no partial credit will be given.
(1) Addition of the first GlcNAc oligosaccharides to the asparagine residue of a protein
(2) Synthesis of phosphatidylcholine
(3) Degradation of misfolded ER protein
(4) O-linked glycosylation

Answer 1

Answer:

EELG

(1) Addition of the first GlcNAc oligosaccharides to the asparagine residue of a protein occurs in the Lumen of the Endopslamic Reticulum

(2) Synthesis of phosphatidylcholine occurs in the Endoplasmic Reticulum

(3) Degradation of misfolded ER protein ossurs in the Lysosome

(4) O-linked glycosylation occurs in the Golgiapparatus

Explanation:

1. The covalent attachment of a carbohydrate to a macromolecule such as proteins or lipids is known as glycosylation.

N-linked glycosylation is a very common form of glycosylation and it occurs in eukaryotes in the lumen of the endoplasmic reticulum.

The addition of the first GlcNAc oligosaccharides to the asparagine residue of a proteinmos an example of N-linked glycosylation.

2. Phosphatidylcholine is synthesized through the CDP-choline pathway which occurs at the cytoplasmic face of the endoplasmic reticulum. Choline entering the cell is immediately phosphorylated by choline kinase, converting choline to phosphocholine.

Phosphocholine is then converted to CDP-choline by the second enzyme in the pathway, CTP:phosphocholine cytidylyltransferase (CT).

The phosphocholine moiety is then added to diacylglycerol in a reaction catalyzed by CDP-choline:1,2-diacylgylcerol cholinephosphotransferase to complete the synthesis of phosphocholine.

3. Lysosomes are the cell organelles which are responsible for the breakdown of proteins as well as other components of the cell. Misfolded proteins are identified and transported to lysosomes through chaperone-mediated autophagy, macroautophagy and endocytosis, where they are then degraded.

4. O-linked glycosylation is a form of glycosylation that occurs in eukaryotes in the Golgi apparatus.