Question

associated with it. Use figure 5.1 as a guide to some of the components. 2. Explain the synthesis of lipids at the ER membrane and how transmembrane proteins are inserted. -- ----- -LStannat ud

Answer 1

1. Synthesis of lipides is the main function of smooth ER. SER produces most of membrane lipids , including both phospholipds and cholesterol.

2. The process of lipids synthesis at the ER menberene-

3. Phospolipds are amphipathic molecules and their synthesis from fatty acyl-CoAs and glycerol 3-phosphate take place at the cytosolic leaflet of ER membrane and are catalyzed by membrane - associatedenzymes . Fatty acids are first converted into CoA ester . Fatty acids from fatty acyl -CoA are esterified to the phosphorylated glycerol backbone , forming phosphatidic acid , whose two long hydrocarbon chain anchor the molecule to the membrane.

-> Insertion of tansmembrane proteins

1. Transmembrane integral membrane proteins are embedded in the membrane by hydrophobic region that spans the lipid bilayer .These proteins are initially inserted into the ER membrane instead of being released into the ER luman. These membrane proteins have four topological classes:
Non cytosolic, Coo cytosolic Type I Type 11 ТЧре Ш Type V

Non cytosolic, Coo cytosolic Type I Type 11 ТЧре Ш Type V

UDP chol Pi cytosol fatty and fatty ace - Phospha – - tidic a ogo Phosphotidal. Cholin cholen ooo (DAG) Dittle ooo COA glycerol 3 COA COA M JER outermonolayer Enner monolayer ER lumen Dia- process of lipids synthesis cet ER memberene