Figure 19.4c Golgi complex

The Golgi body is in communication with the plasma membrane, the reticulum and the nuclear membrane. The vesicles which detach from the dictyosome and which carry secretory products towards the exterior of the cell are the vacuoles of exocytosis.

Proteins from the endoplasmic reticulum are transported to the endoplasmic reticulum – Golgi intermediate compartment and then enter the Golgi apparatus at the cis Golgy network. They then progress to the medial and trans compartments of the Golgi stack, within which most metabolic activities of the Golgi apparatus take place. The modified proteins, lipids, and polysaccharides then move to the trans Golgi network, which acts as a sorting and distribution center, directing molecular traffic to lysosomes, the plasma membrane, or the cell exterior.

The lysosomes. In some cells, but not in all, there are round vesicles called lysosomes (figure 19.5). Lysosome is made of a single membrane like the saccules of Golgi body. It contains digestive or lytic (lysis = to break) enzymes. These enzymes can digest the cell at times and bring the breakdown of harmful and useless substances in the cell. Thus lysosomes play a role in normal processes of decomposition, they control the breakdown of parts of a cell and of foreign particles like bacteria. They are especially abundant in the white blood corpuscles and other kinds of phagocytic cells. While performing their duty many lysosomes break down or lay their own lives. This fact has given them the name of «suicide bags». Lysosomes also take part in destroying the tissues which are no more required. For instance, they bring about regression of mammary glands after they stop producing milk a few months after the delivery of a newborn. Lysosomes were first discovered and studied by a Belgian Biochemist Christian de Duve in 1955. Lysosomes are formed from the breakaway parts of the saccules of the Golgi body. Lysosome - like single-membrane-bound bodies called spherosomes are often quoted as organelles distinct from lysosomes.

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