Golgi Complex

The Golgi complex -- also called the Golgi apparatus or Golgi body -- is the manufacturing-cum-packaging-and-transport unit of the cell. It consists of stacks of hollow, membranous sacs called cisternae, each roughly 0.5 to 1 micrometre in diameter; a cell may have anywhere from a few to several cisternae, depending on how active it needs to be.

Structure and polarity

The two membranes of any given Golgi sac differ from each other in thickness and in molecular make-up, and the whole stack of cisternae has a definite orientation within the cell. Each cisterna has a forming, or 'cis', face -- so called because it faces the same side as the incoming material -- and a maturing, or 'trans', face on the opposite side. Transport vesicles that pinch off from the transitional region of the ER travel to and merge with the cis face of the Golgi stack, adding their contents to the lumen; this is also why Golgi bodies are typically found positioned close to the ER. Once material has been processed, modified and condensed secretions leave the Golgi again through the trans face, packaged as membrane-bound vesicles, sometimes carrying specific surface markers that let them find their correct target cell or organelle.

Function

The Golgi body carries out two broad kinds of work: it modifies secretions that arrive from the ER, and it also manufactures products of its own. Its cisternae hold specific enzymes for specific jobs, and the refining of a product proceeds in an orderly, step-by-step manner as it passes through the stack -- for instance, glycolipids and glycoproteins arriving from the ER lose certain sugars and gain others as they move through, producing a variety of finished products. Golgi bodies in many plant cells also manufacture their own non-cellulose polysaccharides, such as pectin. Whether manufactured in-house or simply modified, all Golgi products ultimately leave the cisternae from the trans face as transport vesicles. …