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# 4.7 The Golgi apparatus

The main functions of the Golgi apparatus are: to sort the proteins and lipids arriving from the ER according to any 'labels' they carry; to complete the glycosylation (and some other modifications) of proteins; and finally, to package the proteins and lipids into vesicles according to one of three main destinations: (1) the lysosomes, (2) the cell (plasma) membrane, or (3) secretion from the cell.

When viewed in the electron microscope, the Golgi apparatus appears as stacks of smooth, flat membranous sacs, known as cisternae, which are slightly curved and surrounded by vesicles of various sizes (Figure 19). The Golgi often has a relatively inconspicuous appearance compared to the RER and its size varies in different cell types.

Figure 19 (a) Electron micrograph of the Golgi apparatus from a rat liver cell. The flattened cisternae can be seen. (b) Schematic drawing of the Golgi apparatus, showing the cisternae and associated transport vesicles.

- Why might the size of the Golgi be different in different types of cells?

- Different cells secrete different amounts of proteins and lipids. Some cells, such as enzyme-secreting cells, for example, secrete large quantities of these proteins and so are specialised for their production and packaging for export. Other types, such as smooth muscle cells, export very little protein.

- Would you expect a cell that does not secrete any lipids or proteins to have a Golgi apparatus?

- Yes, all cells need at least small quantities of lipid and protein to be delivered to their cell membrane. So, all eukaryotic cells have a Golgi apparatus.

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