Protein Sorting & Maturation in the Cell, Lecture 4 PDF

Protein sorting & Mechanism of transport The Endomembrane System An overview of the biosynthetic/secretory and endocytic pathways that unite endomembranes into a dynamic, interconnected network.  Pathwa ys: BIOSYNTHETIC / SECRETORY – CONSTITUTIVE SECRETIO...

Protein sorting & Mechanism of transport The Endomembrane System An overview of the biosynthetic/secretory and endocytic pathways that unite endomembranes into a dynamic, interconnected network.  Pathwa ys: BIOSYNTHETIC / SECRETORY – CONSTITUTIVE SECRETION – REGULATED SECRETION  Endoplasmic Reticulum Schematic diagram showing the stacks of flattened cisternae that make up the rough ER. The cytosolic surface of the ER membrane contains bound ribosomes, which gives the cisternae their rough appearance.  General a Features: network of membrane enclosed tubules and sacs (cisternae) that extends from the nuclear membrane throughout the cytoplasm The entire ER is enclosed by a continuous membrane and is the largest organelle of most eukaryotic cells. Its membrane may account for about half of all cell membranes, and the space enclosed by the ER (the lumen, or cisternal space) may represent about 10% of the total cell volume.  Type s Rough endoplasmic reticulum (RER) smooth endoplasmic reticulum (SER)  FUNCTIONS: Synthes SER of hormone in is steroid s gonad the endocri cells and adren ne of the al cortex. Detoxification in the liver of a wide variety of organic compounds, including barbiturates and ethanol, whose chronic use can lead to proliferation of the SER in liver cells  FUNCTIONS: SER Sequestering calcium ions within the cytoplasm of cells. Ca+ from the Theregulated SER of skeletal release and of cardiac (known as the musclecells 2 sarcoplasmic reticulum in muscle cells) triggers contraction  FUNCTIONS: RER it is the site of synthesis of the proteins, carbohydrate chains, and phospholipids that journey through the membranous compartments of the cell The RER is a major protein processing plant  FUNCTIONS: RER Membrane Biosynthesis in the ER Glycosylation in the Rough Endoplasmic Reticulum Mechanisms that Ensure the Destruction of Misfolded Proteins  FUNCTIONS: RER The ER is also the site of - Protein folding Assembly of multisubunit proteins Disulfide bond formation The initial stages of glycosylation, and The addition of glycolipid anchors to some plasma membrane proteins.  Synthesis of Proteins on Membrane-Bound vs Free Ribosomes one-third of the proteins encoded by a mammalian genome are synthesized on ribosomes attached to the cytosolic surface of the RER membranes These include (a) secreted proteins, (b) integral membrane proteins, and (c) soluble proteins that reside within compartments of the endomembrane system, including the ER, Golgi complex, Overview of protein sorting Secretory pathway: rough ER Golgi secretory vesicles cell exterior The role of the endoplasmic reticulum in protein processing and sorting was first demonstrated by George Palade and his colleagues in the 1960s.