Stages of autophagy, illustration. Autophagy (autophagocytosis) is the natural mechanism that destroys unnecessary or dysfunctional cellular components. The cell nucleus is at left (round), surrounded by folds of the endoplasmic reticulum. The five stages of autophagy shown here (anti-clockwise from bottom left) are: formation of isolation membrane; collection of cellular components for degradation; completion of formation of autophagosome, fusion of autophagosome with lysosome; and formation of autolysosome and degradation of contents. Lysosomes contain hydrolytic enzymes that break down many biological molecules. The 2016 Nobel Prize in Physiology or Medicine was awarded to Japanese cell biologist Yoshinori Ohsumi for his discoveries of mechanisms for autophagy. For this artwork with labels and without arrows, see images C030/3438 and C030/3440.