How does a cell rid itself of defective or malfunctioning organelles?

A cell degrades and recycle its old cell parts by autophagy

Autophagy” (aka “self-eating”) is a biological process when cells are short of nutrient supply. When the cells sense that the environment becomes more challenging or the nutrient source is low, the cells turn on autophagy. In order to obtain the nutrient, the cells have to recycle some of their existed proteins and organelles, especially the misfunctioned ones.

Sometimes, even entire organelles can be packed into autophagosomes for recycling. For example, the special autophagy to degrade bad mitochondria is named “mitophagy.

[In this figure] The process of autophagy.
(1) Once the cell initiates the autophagy, special lipid components (called phagophore) recruit close to the bad proteins/organelles tagged for recycling. (2) More and more phagophores gather around the cellular garbage. (3) Phagophores assemble into a complete vesicle, called the autophagosome. (4) Fusion with the lysosome brings in the digestive enzymes to break down the contents. (5) Bad proteins/organelles are recycled as raw materials for the cells to use.

autophagosome and lysosome

The Function of the Autophagosome and Endosome

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