Fig. 1.

Conceptual model of macroautophagy. A sequestering membrane, termed a phagophore or isolation membrane, forms from the pre-autophagosomal structure. The source of the membrane is unknown but probably includes the endoplasmic reticulum and early secretory pathway. The isolation membrane enwraps cytosol and organelles; on completion, a double-membrane vesicle, the autophagosome or autophagic vacuole, is formed. The autophagosome acquires hydrolytic enzymes by fusing with the lysosome to generate an autophagolysosome, and the inner vesicle of the autophagosome is released into the lumen. The resulting autophagic body is broken down, allowing access to, and degradation and recycling of, the cargo.