How membrane is formed?
Answers
Answer:
phospholipid bilayer. Phospholipids spontaneously form stable bilayers, with their polar head groups exposed to water and their hydrophobic tails buried in the interior of the membrane. ... Plasma membranes, for example, are approximately 50% lipid and 50% protein.
Answer:
Phagophore formation and regulation
The initial step of phagophore membrane formation in mammals remains elusive and has not been adequately defined, whereas in the yeast system this pathway is well defined. Unlike yeast, in the mammalian system there are no reports of preautophagosomal structures (Klionsky, 2007; Yorimitsu & Klionsky, 2005). Target of rapamycin (TOR) kinase acts as a molecular sensor to various stress responses, including hypoxia, insulin signaling, and energy and nutrient depletion, playing a pivotal role in cellular growth and autophagy control (Kamada et al., 2010). Initial nutrient starvation inactivates TOR kinase, resulting in a hypophosphorylated Atg13 that shows an increased affinity for Atg1 kinase (mammalian homolog of Ulk1) and forms a complex with a scaffold-like protein Atg17 (Fig. 2.1; Mizushima, 2010). Starvation treatment enhances the crosstalk between Atg13, Atg1, and Atg17. Atg13 and Atg17 are both required for appropriate monitoring of the kinase activity of Atg1. In turn, Atg1 regulates the transmembrane protein Atg9. The kinase activity of Atg1 is dispensable; however, it controls the dynamics of Atg9 recruitment to the phagophore in an Atg17-dependent pathway (Sekito, Kawamata, Ichikawa, Suzuki, & Ohsumi, 2009; Simonsen & Tooze, 2009). Atg9 is involved in lipid import from different sources like the endoplasmic reticulum (ER), endosomes, mitochondria, golgi bodies, and nuclear envelope and also helps in the assembly of the intact phagophore membrane (Axe et al., 2008; Simonsen & Tooze, 2009; Yorimitsu & Klionsky, 2005).