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In cisternal maturation, a cargo-containing Golgi cisterna changes from early to later identity as its resident proteins change; retrieval of resident enzymes toward earlier compartments helps maintain Golgi apparatus polarity. In the contrasting stable-compartment model, cargo moves between persistent Golgi cisternae in transport vesicles. These mechanisms need not be mutually exclusive.^[ref]

The distinction is between following cargo and following its container. A cargo label encountered first in an early processing environment and later in a late one is compatible with either changing containers or a container changing identity. Finding transport vesicles nearby does not by itself establish which cargo they carry or their direction of travel. Testing cisternal maturation therefore requires evidence about compartment identity and continuity as well as cargo position; a single mechanism should not be assumed for every cargo and biological cell.

Glycosylation attaches carbohydrates to other molecules, including proteins and lipids.^[ref]

Golgi cargo processing includes enzyme-mediated remodeling of attached oligosaccharides. Glycosylation can involve addition of sugars, while processing can also remove them. Different Golgi apparatus regions have different processing enzymes; their substrate requirements constrain the order of possible chemical reactions.^[ref]

An original model makes the importance of ordering explicit. Write a toy carbohydrate chain as $XA$, read with its terminal symbol on the right. Define a trimming function $T$ that removes a terminal $A$, and an extension function $E$ that adds $B$ only when the terminal symbol is $X$. In every other case the corresponding function leaves the chain unchanged. ThenIn particular, $E(T(XA))=XB$ but $T(E(XA))=X$: the two functions do not commute. Each result follows by inspecting the terminal symbol before applying the stipulated rule. These symbols are artificial labels, rather than a natural oligosaccharide sequence or measured enzyme pathway. The example explains why “two processing steps occurred” does not determine the product unless their order and substrate conditions are also specified. In the Golgi apparatus, spatial organization can help arrange successive opportunities for processing.