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Lecture 9 notes

by: Brenna Eisenberg

Lecture 9 notes 327

Marketplace > Syracuse University > Biology > 327 > Lecture 9 notes
Brenna Eisenberg
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Notes from lecture 9- cell components and protein trafficking
Cell Biology
Scott Erdman, John Russel
Class Notes
cellular biology, cells, Biology, Science, Lecture, Lecture Notes
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This 3 page Class Notes was uploaded by Brenna Eisenberg on Thursday October 13, 2016. The Class Notes belongs to 327 at Syracuse University taught by Scott Erdman, John Russel in Fall. Since its upload, it has received 3 views. For similar materials see Cell Biology in Biology at Syracuse University.


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Date Created: 10/13/16
Lecture 9 Thursday, October 6, 20110:42 AM Compartmentsand protein trafficking • Suspected origins for internal membrane compartments: ○ Plasma membrane invaginations-- endomembrane system ○ Endosymbionts-- mitochondria and chloroplasts • Proteins are sorted by mechanisms that use signals • Sorting and trafficking requires energy to move the proteins and to deform the membranes • Nobel prize- signal sequences occur in primary and secondary polypeptides. Signal sequences are necessary and sufficient • Without sorting signals, the proteins will remain in the cytosol Signal is at amino terminus, beginning of protein. Hydrophobic AA's C terminus Patch of positive, basic amino acids. • Nuclear transport: ○ Nuclear pore complexes- allow proteins and mRNAs to traffic across the nuclear membrane ○ Nuclear localization signals (NLS) associate with their NLS receptors. Use GTP hydrolysis for energy. The receptors are cycled in and out of the nucleus.  NLS signals have a string of basic amino acids. Determined by using a mutated T-antigen. Changed 1 amino acid that broke up the string of basic amino acids. Stayed in the cytoplasm. Also determined by using radioactively labeled viruses. Associate the tails with colloidal gold and can see them moving through the nuclear pores ○ Nuclear export signals (NES) ○ Proteins stay folded during import and export • Mitochondria and chloroplast import: ○ Protein with signal sequence Localized receptor in the membrane Lecture 9 Page 1 ○ Localized receptor in the membrane ○ Transmembrane translocator complex ○ Proteins unfolded as they are transported across mitochondrial membrane ○ Signal sequence is removed by peptidase when inside. If it gets outside the membrane, there is no way for it to get back inside. ○ Mitochondrial signal sequence is an amphipathic alpha helix. Found at amino terminus, scattered basic amino acids. The helix shape causes the basic amino acids to be on the same side. • ER import and vesicle traffic ○ The ER is the first decision point for protein destinations ○ Vesicle traffic- coats and SNAREs ○ Golgi- major decision point for paths. Similar to a bus station ○ Endosome- other major bus station of the cell for proteins ○ Proteins can be directed for translocation into the ER by signal recognition particle (SRP) and receptors, and translocation channels. ○ Ribosomes associate with the ER because proteins that bear the signal sequence are cotranslationally inserted into the ER membrane  Causes the ribosome to pause and be trafficked to ER surface ○ Proteins are modified by glycosylation in the ER & golgi. Disulfide bonds are also catalyzed here.  Glycosylations are added by oligosaccharide protein transferases ○ The folding and membrane insertion is assisted by chaperones • Plasma membrane proteins must be oriented in the correct way to function • Start and stop transfer sequences specify insertion of hydrophobic transmembrane helices into ER membrane ○ Single pass and multipass transmembrane domain proteins • The nature of the signals is understood by cell free reconstituted systems • Unfolded protein response pathway- signaling pathway that helps quality control by increasing chaperone activities • Cystic fibrosis is caused by stringent quality control by chaperones. The proteins are slightly misfolded and are rapidly degraded whether or not they are functional. The protein is a chloride transporter • Vesicle transport: ○ Vesicles move soluble & membrane associated proteins between cellular compartments ○ Secretory pathway:  Forward flow- ER → golgi → plasma membrane → lysosome  Retrograde flow- golgi → ER "retrieval" ○ Endocytic pathway: plasma membrane → endosome → lysosome → plasma membrane ○ Vesicles are formed by the action of protein coats  The coats deform the membranes so they can be pinched off by dynamin. Uses GTP hydrolysis  Typically clathrin  Associate with adaptor proteins and cargo receptors  Dynamin helps cut off the vesicle from the parent membrane ○ Rabs, tethers, v-SNAREs, and t-SNAREs are responsible for targeting and fusion specificity of vesicles to their destinations  v-SNARE present on the vesicle  t-SNARE present on target membrane that the vesicle will dock to  The shapes of the SNAREs prevent incorrect docking  Rabs recognize tethers, then the SNAREs drive the fusion reaction and help provide membrane specificity  Different coats are present in different origins and destinations in the cell ○ Trans-face of the golgi: sorting station similar to the endosome ○ Regulated exocytosis-the vesicles are made to wait for a signal to fuse. Ex- neurotransmitterscausing the release of ions ○ Unregulated exocytosis- constitutive secretion ○ The pathways were studied with mutants in the secretory pathway and were temperature sensitive. Shows that the proteins accumulated at specific steps in the pathway. Also used reconstituted protein sorting in vitro • Endocytosis can be receptor mediated. Brings material into the cell ○ Ex- LDL receptors bring in LDL cholesterol. Trafficking to the endosome,then into the lysosome.The receptors are recycled back into the plasma membrane. ○ The early endosome is like the golgi and is a sorting point • Lysosome has an acidic environment. Needed for the proper function of certain proteins such as lipases, nucleases, etc. Proto ns are brought into the lysosome by ATP hydrolysis. Lecture 9 Page 2 Lecture 9 Page 3


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