Endomembrane system
Endoplasmic reticulum, golgi bodies, lysosome and peroxisomes.
To start with Endoplasmic reticuum ER.
There are two types of ER. Smooth ER or SER and Rough ER or RER.
RER made up of cisternae with ribosomes attached and SER are tubular and lack ribosomes.
Important function of RER:
Glycosylation of protein.
Folding of protein.
Removal of mis folded protein.
Assembly of multi subunit protein.
When protein is made on ribosomes attached to ER and is transported into ER simultaneously then this movement is caled cotranslational translocation.
When protein is made on free ribosomes and then it is translocated in ER then the movement is called post translational translocation.
Glycosylation of protein or addition of carbohydrates on protein.
All N linked glycosylation of protein takes place in RER.
In this the carbohydrate will attach to NH2 of asparagine always.
All asparagine which are part of Asp-X-Ser will be N linked glycosylated. X can be any amino acid except proline and Ser is serine.
O linked glycosylation always takes place in Golgi body.
N linked glycosylation is of two types 1. Core glycosylation or initial glycosylation and 2. modification of added sugar.
Core Glycosyalation:
It always start with addition of N acetyl glucose amine or NAG by the help of enzyme oligosaccharyl transferase. This enzyme add 15-16 sugars to protein.
ER membrane has Dolichol phosphate and NAG and mannose are added to it towards cytosol.
So two NAG and 5-7 mannose are added towards cytosolic side of ER.
Then translocation of oligosaccharide from cytosol to ER lumen takes place with the help of Flippase.
Desired number of saccharides including mannose, glucose are added in luminal side of ER.
With the help of enzyme oligosaccharyl transferase completed core of oligosaccharide is transffered to asparagine residue of protein.
Finally certain sugar residues are added or removed for final processing.
Endoplasmic reticulum, golgi bodies, lysosome and peroxisomes.
To start with Endoplasmic reticuum ER.
There are two types of ER. Smooth ER or SER and Rough ER or RER.
RER made up of cisternae with ribosomes attached and SER are tubular and lack ribosomes.
Important function of RER:
Glycosylation of protein.
Folding of protein.
Removal of mis folded protein.
Assembly of multi subunit protein.
When protein is made on ribosomes attached to ER and is transported into ER simultaneously then this movement is caled cotranslational translocation.
When protein is made on free ribosomes and then it is translocated in ER then the movement is called post translational translocation.
Glycosylation of protein or addition of carbohydrates on protein.
All N linked glycosylation of protein takes place in RER.
In this the carbohydrate will attach to NH2 of asparagine always.
All asparagine which are part of Asp-X-Ser will be N linked glycosylated. X can be any amino acid except proline and Ser is serine.
O linked glycosylation always takes place in Golgi body.
N linked glycosylation is of two types 1. Core glycosylation or initial glycosylation and 2. modification of added sugar.
Core Glycosyalation:
It always start with addition of N acetyl glucose amine or NAG by the help of enzyme oligosaccharyl transferase. This enzyme add 15-16 sugars to protein.
ER membrane has Dolichol phosphate and NAG and mannose are added to it towards cytosol.
So two NAG and 5-7 mannose are added towards cytosolic side of ER.
Then translocation of oligosaccharide from cytosol to ER lumen takes place with the help of Flippase.
Desired number of saccharides including mannose, glucose are added in luminal side of ER.
With the help of enzyme oligosaccharyl transferase completed core of oligosaccharide is transffered to asparagine residue of protein.
Finally certain sugar residues are added or removed for final processing.
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