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Lecture 3

Lecture 3 - Organelle Structures .docx

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Jane Mitchell

Lecture 3 – Organelle Systems The Endomembrane System  Endosomes, Lysosomes, Golgi, Endoplasmic Reticulum  Temporal Linkage Biosynthetic/Secretory Pathways  The ER makes the proteins  The proteins are placed into a vesicle and move to the Golgi  The Golgi glycosylates the protein or modifies it  The proteins then is placed in another vesicle  The vesicle now fuses with the plasma membrane  Protein is now outside the cell  Can be regulated or constitutive o Constitutive = non stop excretion; if you have it, excrete it o Regulated pathway = proteins are stored until a stimulus is sensed leading to excretion Endocytic pathway  The plasma membrane “eats” and a vesicle is formed  The vesicle travels to Lysosome for digestion Protein Sorting  Pulse Chase experiment o Fire a pulse of radioactive amino acids o Chase that pulse with non-radioactive amino acids o Follow that path to see where the proteins go  Post translational sorting o A protein is made in the cytosol o The protein is then sorted to the mitochondria or chloroplast o The proteins tend to be unfolded until they reach the correct place  Co-Translational Process o While protein is being made, head of the protein is already being inserted into the ER  A signal sequence is on the growing protein  The signal sequence is recognized by a protein translocator  The translocator moves the protein through the membrane into the ER  When the process is complete, the signal peptidase cleaves the signal sequence from the protein  The cleaved signal sequence is now no longer connected to the protein  The protein is now in the ER  The protein in the lumen can then be secreted to where it is needed Protein Sorting Systems 1. Gated System (Post translation)  Proteins move between cytosol and nucleus through NPC (Nuclear Pore Complex)  NPC = a bunch of proteins that makes a pore in the nuclear membrane  Pore moves proteins in a regulated manner; proteins folded before insertion 2. Transmembrane System  Protein translocators are needed to move a protein across a membrane  Eg. Endoplasmic Reticulum, mitochondria, plastids, peroxisomes  Bold = post translational system  Peroxisomes proteins have been folded before insertion,  mitochondrion & Plastids proteins are unfolded until insertion 3. Vesicular System  The protein is in a membrane of the vesicle, or in the lumen of the vesicle  The vesicle moves to the appropriate place and delivers the protein Signal Sequences  Signal Sequence = a part of the protein that tells the protein where to go  Signal sequences are recognized by sorting receptors  Signal sequence may be cleaved and is left in the membrane  The signal sequence is then destroyed by other enzymes Tran
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