Post-translational Modification and Collagen Biosynthesis Quiz

See Glycosylation. Option E is correct. Post-translational modification means a chemical change made to a protein after it has been built by translation. Glycosylation is one of the most common: an enzyme covalently attaches a carbohydrate, in the form of a sugar or a short chain of sugars (a glycosyl group), to a protein, forming a glycosidic bond (a bond that links a sugar to another molecule). It needs many enzymes and steps, and is under strict enzymatic control. There are two main types. In N-linked glycosylation, which takes place in the endoplasmic reticulum, the sugar is attached to the nitrogen atom of an asparagine residue. In O-linked glycosylation, which takes place in the Golgi apparatus, it is attached to the hydroxyl group of serine or threonine. Glycosylation helps proteins to fold correctly, makes them more stable and affects how they interact with other molecules. Do not confuse it with glycation, in which a sugar such as glucose attaches to a protein without an enzyme, as in glycated haemoglobin (HbA1c).

• Definition: glycosylation is the covalent attachment of a carbohydrate to a protein after it has been made.
• Types: N-linked glycosylation occurs in the ER on asparagine, and O-linked glycosylation occurs in the Golgi on serine or threonine.
• Contrast: glycation is non-enzymatic, as in glycated haemoglobin (HbA1c).