Final answer:
Mannose in glycan chains in the Golgi may be replaced by another sugar such as glucose, fucose, galactose, or sialic acid, but the specific replacement sugar is not provided in the reference information.
Step-by-step explanation:
The molecule that can replace mannose in glycan chains in the Golgi apparatus during protein modification is typically another sugar. More specific information about which sugar replaces mannose is not provided in the reference information. However, in general, once oligosaccharides begin synthesis in the rough endoplasmic reticulum (RER), they are linked to membrane proteins and are further modified in the Golgi apparatus. Terminal glycosylation occurs here, whereby additional sugars are attached to complete glycoprotein synthesis. Various enzymatic processes are involved that can replace mannose with other sugars like glucose, fucose, galactose, or sialic acid depending on the specific glycosylation process and enzyme activity within the Golgi apparatus.