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synthesis of membran
| Question | Answer |
|---|---|
| What are two features of a translocator? | A plug and a seam |
| Where does the polypeptide grow in the translocator? | In the plug |
| How does the signal peptide and polypeptide chain leave the translocator? | Through the opened seam |
| What are the two sides of a membrane? | luminar, cytosolic |
| What three functions can the signal sequences direct proteins to do? | import, export and localize proteins |
| What is the difference between co-translational translocation and post-translationl translocation? | Proteins are made and then put into cellular membrane (post) proteins are translated at the site and placed immediately into membrane (co) |
| Difference between rough and smooth ER function | Rough - proteins are synthesized Smooth - membranes are synthesized |
| briefly explain co-translational translocation | ribosomal subunits attach directly to the translocateor that is imbedded in the ER membrane. When proteins are translated, the are grown inside of the ER lumen. When finished, the signal peptadiase detaches, as well as signal peptide |
| briefly explain post-translational translocation | Proteins are synthesized int he cytosol of the cell, then localized to ER membrane and transported into the cell via translocator |
| What initiates synthesis of membrane proteins? | SRP binds to ribosomal unit performing translation, causing it to pause |
| Where does the SRP-bound translation unit go? | It is brought to a SRP receptor protein, where it is then moved to the protein translocator |
| What are three major functions of SRP? | 1. Recognizes signalling sequence and binds with met on growing protein 2. binds to large subunit 3. recognizes SRP receptor |
| What is a secreted protein? | a protein that exists fully inside of the ER. it has a cleaved signal sequence |
| What is a single-pass membrane protein? Name specific parts | A single pass protein has one transmembrane unit with parts extending inside and outside of the cell. A stop transfer sequence tells the translocator when to release the protein into the membrane |
| What charges on the stop transfer sequence exist in which part of the cell? | Negative - lumen positive - cytosol |
| How can internal signal sequences direct production of membrane proteins? | if they have certain charges, they can dictate which end (C or N term) is internalized |
| How are double pass proteins created? | Start transfer and stop transfer sequences are hydrophobic. They dictate where the protein passes through the membrane |
| How are multipass proteins created? | Alternating start/stop sequences |
| How does glycosylation start | lipid linked oilgosaccharides exist in the membrane - they are transferred with oligosaccharyl transferase to an asparagine (N) |
| What is the typical amino acid sequence for N-linked glycosylation | Asparagine-X-(serine or threonine) |
| What is the initial oligosaccharide attached to? | Dolichol |
| What is the hierarchy of attached saccharides, starting with N-bound? | N-acetylglucosamine, mannose, glucose |
| Where do proteins acquire their correct folding? | In the ER |
| What do unfolded proteins first bind to? | They bind to calnexin, which is a transmembrane chaperone |
| What does calnexin do? | Binds to the glucose in the N-linked structure and removes it with glucosidase |
| What if the protein is not correctly folded? | Glucosyl transferase adds the glucose again using UDP-glucose |
| What are three examples of other modifications made to proteins | 1. association with BiP chaperone for facilitated translocation and protein folding 2. formation of disulfide bonds catalyzed by disulfide isomerase 3. formation of multimer protein complexes |
| Where are misfolded proteins transported? | To the cytoplasm through an ER translocator |
| What happens to misfolded proteins when in the cytosol? | N-glycanase removes oligosaccharides protein gets ubiquitinated protein broken down in proteasome |
| Where are phospholipids assembled? | cytoplasmic side of the smooth ER |
| Where is GPI anchored and what does it do? | It is anchored to one layer in lumen of ER. It binds to the anchored protein and serves as a new anchor site for the protein. |
Created by:
neeck
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