Lysosomes cycle

In neurons and non-neuronal cells, kinesin is associated with a variety of MBOs, ranging from synaptic vesicles to mitochondria to lysosomes. In addition to its role in fast axonal transport and related phenomena in non-neuronal cells, kinesin appears to be involved in constitutive cycling of membranes between the Golgi and endoplasmic reticulum. However, kinesin is not associated with all cellular membranes. For example, the nucleus, membranes of the Golgi complex and the plasma membrane all appear to lack kinesin. Kinesin interactions with membranes are thought to involve the light chains and carboxyl termini of heavy chains. However, neither this selectivity nor the molecular basis for binding of kinesin and other motors to membranes is well understood. 

Viruses have many modes of life. They enter cells in various ways. Some enter through coated pits from which they are taken into lysosomes via endocytosis. Others are literally injected into the cells (See Box 7-C). Within cells some viruses are assembled in the nucleus, some in the cytoplasm, and some in membranes. The typical life cycle of a virus leads to rapid formation of large numbers of progeny. Within 20 minutes after entrance into a bacterial cell, a bacteriophage can... 

ATP plays a central role in cellular maintenance both as a chemical for biosynthesis of macromolecules and as the major soirrce of energy for all cellular metabolism. ATP is utilized in numerous biochemical reactions including the eitric acid cycle, fatty acid oxidation, gluconeogenesis, glycolysis, and pyruvate dehydrogenase. ATP also drives ion transporters sueh as Ca -ATPase in the endoplasmic reticulum and plasma membranes, H+-ATPase in the lysosomal membrane, and Na+/K+-ATPase in the plasma membrane. Chemieal energy (30.5 kJ/mol) is released by the hydrolysis of ATP to adenosine diphosphate (ADP). 

Tobin DJ, Foitzik K, Reinheckel T, Mecklenburg L, Botchkarev VA, et al. The lysosomal protease cathepsin L is an important regulator of keratinocyte and melanocyte differentiation during hair follicle morphogenesis and cycling. Am. J. Pathol. 2002 160 1807-1821. 

In eucaryotic cells, glycolysis, gluconeogenesis and fatty acid synthesis takes place in the cytosol, while the Krebs cycle is isolated within mitochondria glycogen is made in glycogen granules, lipid is synthesized in the endoplasmic reticulum and lysosomes carry on a variety of hydrolytic activities. As in procaryotic cells, ribosomes in the cytosol are the site of protein synthesis. 

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