BIOL 225 Lecture 17- Chapter 8 Endomembrane
BIOL 225 Lecture 17- Chapter 8 Endomembrane BIOL 225
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This 3 page Class Notes was uploaded by MelLem on Thursday April 14, 2016. The Class Notes belongs to BIOL 225 at Simmons College taught by Dr. Lopilato in Fall 2016. Since its upload, it has received 19 views. For similar materials see Cell Biology in Biology at Simmons College.
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Date Created: 04/14/16
Cell Biology BIO 225 Lecture 17 Chapter 8 – Endomembrane System • Components: o ER – endoplasmic reticulum o Golgi Apparatus o Endosomes o Lysosomes o Vacuoles • Budding and fusion of vesicles from one compartment to the next • Adding carbohydrates to proteins and lipids • Transfer proteins • Transfer of membrane lipids Insertion of membrane proteins and lipids • Proteins stop transfer sequences • Models for protein orientation in the membrane o C terminus in cytoplasm o C terminus in lumen of ER • Lipid synthesis in ER • Lipid delivery to endomembranes and plasma membranes Asymmetry of membrane proteins • Synthesized in ER • Orientation of protein in vesicle • Orientation of protein in membrane Degradation of abnormal proteins • Abnormal proteins are translocated out of the ER • Tagged in cytoplasm with ubiquitin protein • Sent to proteasome and degraded Lysosomes: • Single membrane bound organelles • Lysosomes contain acid hydrolases which can digest every type of biological molecule. • The low pH optimum of these enzymes is maintained by a proton pump (H+ ATPase) Targeting enzymes to the lysosome: • Tag is mannose-‐6-‐phospahe • Receptor for mannose-‐6-‐P tagged proteins in the trans golgi • Deliver proteins to endosome ▯ lysosome • Defects and diseases o I-‐cell disease – no tag so lysosomal proteins secreted from the cell o Lysosomal storage diseases – no enzyme to digest sphingolipid compounds. • Lysosomal malfunctions can have serious effects on human health • Lysosomal storage disorders result from the absence of specific lysosomal enzymes thus allowing undigested material to accumulate. • Treatment for these diseases may include-‐ enzyme replacement therapy Endocytosis: • Receptor mediated endocytosis • Clathrin coated pits • Early endosomes • Late endosomes • Lysosome-‐ terminal component of endocytic pathway Different coats bring vesicles to different locations • Clathrin coats for endocytosis and transport of lysosomal enzymes to the lysosome. • COPII coated vesicles go from ER to golgi • COPI – coated recycling vesicles bring back to the ER Targeting and Fusing Vesicles: • Movement of the vesicle toward specific target compartment • Tethering vesicles to the target compartment o Process mediated by g-‐proteins called rabs. o Rabs play a key role in vesicles targeting by recruiting specific tethering proteins • Docking vesicles to target organelle – paring v-‐SNARE to t-‐SNARE • Fusion – pairing lead to pulling the two lipid bilayers together Post-‐transitional Localization • Proteins synthesized in the cytoplasm on free ribosomes • Proteins remain in the cytoplasm • Proteins directed to organelles o Unfold proteins and transport into mitochondria and chloroplasts o Folded proteins transported into peroxisome by unknown mechanism. • Intermembrane space – between inner and outer membrane • The tags for the chloroplasts are much more complex • The tags once they’re in their proper destination, they get “cut” off Peroxisomes: • Membrane bound vesicles 0.1-‐10um in diameter • Contain oxidases and generate H2O2, but they also contain catalase to break down H2O2. • Oxidize fatty acids (24-‐26 carbon chains) • Synthesize special phospholipids called plasmalogens found in the myelin sheath of nerves. Plasmalogens have an ether linkage between the fatty acids and glycerol rather than an ester linkage. • Peroxisomes = glyoxysomes in plant seedlings. Are a specialized type of peroxisome that converts fatty acids to carbohydrates o Only plant seedlings can do this • Peroxisome targeting signal • MPTS – for the membrane
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