4.3 The Endoplasmic Reticulum, Golgi Apparatus, and Lysosomes are part of an extensive endomembrane

4.3 The Endoplasmic Reticulum, Golgi Apparatus, and Lysosomes are part of an extensive endomembrane

1. Overview

   • Cells have extensive sets of intracellular membranes which compose the endomembrane system
     • First discovered in the late 1800s
     • Contains: the ER, golgi, and lysosomes.

2. How are the cell membranes synthesized?

   • Membranes and proteins assembled in the ER
     • ER: contains the enzymes involved in lipid synthesis (lipids manufactured in the ER and inserted into the organelle's own membranes_
   • Transpermeable proteins have enough hydrophobic surfaces that they are also inserted into the ER membrane while being made
   • Lumen: proteins that will be secreted by a cell end up in this internal cavity where they are then packaged for vesicular release from the cell

3. How are organelle membranes maintained?

   • Membrane lipids and proteins synthesized in ER must be transported through the network to the vesicles
     • Vesicles: cargo-bearing, pinch off of one set of membranes and travel along microtubule tracks to the next set of membranes where they fuse with these structures

4. Golgi apparatus

   • Functions as a molecular assembly line in which membrane proteins undergo extensive post-translational modification
   • Many reactions involve the addition of sugar residues to membrane proteins and secreted proteins
   • cis-Golgi: vesicles that bud off from the ER fuse with the closet golgi membranes
   • trans-Golgi: cis-golgi until reach the end of the assembly line at the farthest sacs from the ER

5. Lysosomes

   • Break down molecules into smaller parts which are then recycled
   • Have enzymes called hydrolases that can digest proteins, nucleic acids, lipids, and other complex sugars
   • Endocytosis: Vesicles that bud off from the plasma membrane via this are also sent to lysosomes where their extracts are procceds