With regard to cell biology, one area of focus that has shifted back and forth 
over the years has been the relative emphasis on catabolic versus anabolic 
processes: the breakdown of glucose, the synthesis of DNA, the oxidation of 
pyruvate, the biogenesis of membranes, protein degradation, and protein 
synthesis. Historically, the majority of studies concerned with degradation 
dealt with the production of energy; however, the analysis of the 
ubiquitin-proteasome system revealed the importance of protein degradation for 
controlling various aspects of cell physiology. The ubiquitin-proteasome system 
is limited primarily to targeting individual proteins for destruction, but cells 
also have to deal with larger structures that are damaged, potentially toxic or 
superfluous, and these substrates, including entire organelles, are the purview 
of autophagy. As a general definition, autophagy encompasses a range of 
processes in which the cell degrades parts of itself within the lysosome (or the 
analogous organelle, the vacuole, in yeast and plants), followed by the release 
and reuse of the breakdown products. Thus, autophagy is in part a mechanism for 
cellular recycling, but such a definition belies the importance of the different 
autophagic processes in cell and organismal function and homeostasis. Indeed, 
defects in autophagy are associated with many human diseases and metabolic 
disorders. Here, we provide a brief overview of the mechanism of autophagy and 
some of the physiological roles in which this process is involved.