Autophagosome

An autophagosome is a spherical structure with double layer membranes. It is the key structure in macroautophagy, the intracellular degradation system for cytoplasmic contents (e.g., abnormal intracellular proteins, excess or damaged organelles, invading microorganisms). After formation, autophagosomes deliver cytoplasmic components to the lysosomes. The outer membrane of an autophagosome fuses with a lysosome to form an autolysosome. The lysosome's hydrolases degrade the autophagosome-delivered contents and its inner membrane.^[2]

The formation of autophagosomes is regulated by genes that are well-conserved from yeast to higher eukaryotes. The nomenclature of these genes has differed from paper to paper, but it has been simplified in recent years. The gene families formerly known as APG, AUT, CVT, GSA, PAZ, and PDD are now unified as the ATG (AuTophaGy related) family.^[3]

The size of autophagosomes vary between mammals and yeast. Yeast autophagosomes are about 500-900 nm, while mammalian autophagosomes are larger (500-1500 nm). In some examples of cells, like embryonic stem cells, embryonic fibroblasts, and hepatocytes, autophagosomes are visible with light microscopy and can be seen as ring-shaped structures.^[2]