<P> Vesicles are small membrane - enclosed transport units that can transfer molecules between different compartments . Most vesicles transfer the membranes assembled in the endoplasmic reticulum to the Golgi apparatus, and then from the Golgi apparatus to various locations . </P> <P> There are various types of vesicles each with a different protein configuration . Most are formed from specific regions of membranes . When a vesicle buds off from a membrane it contains specific proteins on its cytosolic surface . Each membrane a vesicle travels to contains a marker on its cytosolic surface . This marker corresponds with the proteins on the vesicle traveling to the membrane . Once the vesicle finds the membrane, they fuse . </P> <P> There are three well known types of vesicles . They are clathrin - coated, COPI - coated, and COPII - coated vesicles . Each performs different functions in the cell . For example, clathrin - coated vesicles transport substances between the Golgi apparatus and the plasma membrane . COPI - and COPII - coated vesicles are frequently used for transportation between the ER and the Golgi apparatus . </P> <P> Lysosomes are organelles that contain hydrolytic enzymes that are used for intracellular digestion . The main functions of a lysosome are to process molecules taken in by the cell and to recycle worn out cell parts . The enzymes inside of lysosomes are acid hydrolases which require an acidic environment for optimal performance . Lysosomes provide such an environment by maintaining a pH of 5.0 inside of the organelle . If a lysosome were to rupture, the enzymes released would not be very active because of the cytosol's neutral pH . However, if numerous lysosomes leaked the cell could be destroyed from autodigestion . </P>

Mitochondria and chloroplasts are part of the endomembrane system of the eukaryotic cell