Cheat Sheet Test 2 - The aggregate current crossing the...

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The aggregate current crossing the membrane of an entire cell does not indicate the degree to which a typical individual channel is open but rather the total number of channels in its membrane that are open at any one time. By using a variety of different import receptors and adaptors, cells are able to recognize the broad repertoire of nuclear localization signals that are displayed on nuclear proteins. The ER has a central role in both lipid and protein biosynthesis, and it also serves as an intracellular Ca store that is used in many cell signaling responses. The ER membrane is the site of production of all the transmembrane proteins and lipids for most of the cell’s organelles. The ER membrane also makes most of the lipids for mitochondrial and peroxisomal membranes. Smooth ER specializes in lipid metabolism; the expanded smooth ER accommodates the enzymes that make cholesterol and modify it to form the hormones. Transmitter-gated channels are insensitive to membrane potential. Instead they produce local permeability changes. Cl much higher outside than outside. The NMDA recetptor channeles open only when glutamate is bound to the receptor and the membrane is strongly depolarized. Depolarization required to release Mg. LTD – modest Ca levels activate protein phosphates LTP – high Ca levels Mitochondrial signal sequence – positively charged amino acids alternate with hydrophobic ones ER signal includes hydrophobic amino acids Nuclear localization signal – positive amino acid lys + arg, located anywhere Thus, it seems that the information required to construct an organelle does not reside exclusively in the DNA that specifies the organelle’s proteins. Because many cell proteins are too large to diffuse passively through the NPCs, the nuclear compartment and the cytosol can maintain different complements of proteins. Ran-GAP located in cytosol: GTP-GDP Ran-GEF located in nucleus: GDP-GTP If they reach the nuclear side of the pore complex, Ran-GTP bind to them, and, if they arrive loaded with cargo molecules, the Ran-GTP binding causes the import receptors to release their cargo. Nuclear export occurs by Ran-GTP in the nucleus promotes cargo binding to the export receptor, rather than dissociating it. 1. (6) Describe one similarity and one difference between small ion transport and nuclear transport. Any of: Both use asymmetric distributions across the membrane to power directed transport. Small ions/molecules can passively move across them either. What can be transported may be limited by size. Anything else reasonable. Any of: Ion transport is usually specific while nuclear transport is much more varied. Channels are not always open while NPCs are always permeable to small molecules. Channels and pumps move small molecules while NPCs can transport huge multi-molecule complexes. Anything else reasonable.
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This note was uploaded on 04/11/2008 for the course BIO 320 taught by Professor Staff during the Spring '08 term at University of Texas at Austin.

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Cheat Sheet Test 2 - The aggregate current crossing the...

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