Even though autophagy has been known for over 40 years, the molecular machinery behind this process has been largely unknown until recently. Today over ~30 autophagy-related genes (ATG-genes) are known. Three main purposes for autophagy have been identified: nutrient starvation: Decreased levels of amino acids can induce the autophagic. Autophagy plays a role in the destruction of some bacteria within the cell, and in detection of virus via pathways of the innate immune system housekeeping process: proteins and organelles are recycled. Autophagy is not directly a death pathway, like apoptosis, but rather a self-cannibalisation pathway. Utilizing lysosomal degradation, autophagy is responsible for cleaning the cell of unwanted proteins and degrades even complete cellular organelles.

Three types of degradation are known: Pexophagy, autophagy selective for degradation of peroxisomes, Mitophagy, autophagy selective for degradation of mitochondria, Xenophagy, autophagy selective for degradation of intracellular bacteria and viruses. Autophagy can be induced by both internal and external stimuli. A number of tumour-suppressor proteins control autophagy (e.g. Beclin-1 and PTEN) decrease in autophagy would lead to tumour progression

Three autophagic processes are known:
1) Microautophagy happens when lysosomes directly engulf cytoplasm.
2) Macroautophagy involves formation of a double-membrane structure called the autophagosome which delivers cytosolic material into the lysosome for degradation.
3) Chaperone-mediated autophagy (CMA) is characterized by its selectivity regarding the specific substrates (cytosolic proteins) degraded.

Microautophagy happens when lysosomes directly engulf cytoplasm. Macroautophagy involves formation of a double-membrane structure called the autophagosome which delivers cytosolic material into the lysosome for degradation. Chaperone-mediated autophagy (CMA) is characterized by its selectivity regarding the specific substrates (cytosolic proteins) degraded. Only proteins that have a consensus peptide sequence get recognized and degraded. In the process the substrates for degradation are transferred into the lysosome one-by-one. This process does only degrade proteins not entire organelles.

Autophagy can be induced by both internal and external stimuli. The nutrient sensor mTOR has an inhibitory effect on autophagy, under starvation conditions, mTOR is inactivated – leading to the inhibition of autophagy being released. Hence nutrient depletion triggers autophagia. Only proteins that have a consensus peptide sequence get recognized and degraded. In the process the substrates for degradation are transferred into the lysosome one-by-one. This process does only degrade proteins not entire organelles. Autophagy is part of everyday normal cell growth and development and is essential in helping to maintain the balance between the increase and decrease in the number of a cell content.