test_3_review

test_3_review - Endoplasmic Reticulum Proteins made on...

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Endoplasmic Reticulum Proteins made on ribosomes in the cytosol and sorted to organelles by sorting signals Mitochondria and chloroplasts divide with cell division and divided between progeny cells Nuclear envelope, ER, and golgi break down during mitosis into vesicles which reform organelles in progeny Proteins delivered to the nucleus, mitochondria, chloroplasts, and peroxisomes directly from choloroplast Proteins delivered to golgi, lysosomes, endosomes, and plasma membrane indirectly from ER Ways proteins enter membrane-bound organelles: 1. move fully-folded through a pore (how they enter nucleus) sorting signals needed 2. can be threaded as unfolded polypeptide chains through a translocation channel (how they enter ER, mitochondria, chloroplasts and peroxisomes) sorting signals needed 3. delivered to the organelle in the membrane of the lumen (enclosed space) of a vesicle (how the enter Golgi, endosomes, lysosomes, and plasma membrane) may not need a sorting signal ER- large organelle. Three-dimensional network of tubes and flattened bubbles. Most is studded with ribosomes (rough ER) the rest is smooth ER (contains enzymes that make lipids) ER lumen- space enclosed by the single ER membrane Proteins that will be delivered to Golgi, endosomes, lysosomes, plasma membrane, ER, and secreted protein are inserted into the ER before translation is finished (translocation-co translational). Ribosomes making the proteins attach to the ER membrane. Have sorting signals that target the ribosomes that make them to the Er membrane Signal is part of the polypeptide chain-generally at the N-terminus and has 15-20 AA including a core of eight or more w/ hydrophobic side chains Signal recognition particle (SRP) in the cytosol recognizes the signal sequence. Complexes of six polypeptide chains and a small RNA with a hydrophobic pocket of methionine ER import: 1. ribosomes free in the cytosol 2. SRP recognizes the signal sequence of a membrane protein emerging from the ribosome. Protein synthesis stops 3. SRP binds to SRP receptor on ER membrane, bringing the ribosome to the ER 4. Signal sequence is displaced from SRP and SRP is released 5. Synthesis continues and protein is inserted through translocation channel made of proteins in the ER membrane. N-terminal signal peptides cut off by signal peptidase, and released and degraded Soluble proteins that are secreted or function in the lumen of ER, golgi, endosomes, and lysosomes pass completely through translocation channel when translation is done. Proteins that will span the ER, golgi, endosomal, lysosomal, or plasma membrane a released laterally from translocation channel into ER membrane (another signal does this)
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Proteins that span membrane only once have N-terminus on non cytoplasmic side and C- terminus on cytoplasmic side. Orientation is preserved as it moves in vesicles to target protein Folding begins co transitionally and continues when protein is released from ribosome. Folding assisted by chaperones-mediate correct assembly
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test_3_review - Endoplasmic Reticulum Proteins made on...

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