Final answer:
Autophagy is mainly increased by starvation as cells recycle components for survival. It involves autophagosome formation and is influenced by factors like phosphorylation of eIF-2 and ubiquitin-mediated degradation, while substances like homocysteine can inhibit autophagy.
Step-by-step explanation:
The process of autophagy is increased by various cellular stresses, one major trigger being starvation. When cells are deprived of nutrients, they initiate autophagy as a survival mechanism by degrading and recycling their own components, including organelles and cytosolic proteins. This process involves the formation of autophagosomes that encapsulate cellular components, which then fuse with lysosomes where the contents are degraded. Factors like increased levels of phosphorylation of eIF-2 in neurodegenerative diseases and the activity of ubiquitin in targeting proteins for degradation also play roles in protein turnover and autophagy. Additionally, homocysteine has been shown to inhibit autophagy and contribute to the formation of abnormal proteins, while the regulation of protein turnover is crucial to maintaining cellular homeostasis, where the balance is maintained by synthesis and degradation.