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mcdb100finalquestans_08W - MCDB 100 Final Study Questions...

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MCDB 100 Final Study Questions 2/28/ 2008 O'Lague 1. What is a signal sequence and its role in cell processes? Ans: Amino acid sequence that directs a protein to an organelle. 2. Name three ways membrane–enclosed organelles import proteins and give examples. Ans: transport through nuclear pores (nucleus), transport across membranes (mito), transport by vesicles (ER, Golgi). 3. What is the signal recognition particle and it role in protein trafficking? Ans: RNA-protein complex that binds signal sequence-mRNA-ribosome complex and directs it to the ER. 4. Propose two experiments to show that the nuclear localization sequence (NLS) is both necessary and sufficient. Ans: Remove NLS from a protein destined for the nucleus and add a NLS to a cytoplasmic protein. 5. What is the role of GTP in transport of proteins into the ER? Ans: Acts as a switch allowing conformational changes that move components relative to each other in ER complex for transport. 6. What 3 classes of proteins are targeted into the ER and their destination? Ans: proteins destined for lysosomes, proteins in vesicles to be secreted by signals and constitutive secretion including those that will stay in the cell membrane. 7. What are chaperones and what is their function? Ans: ATP-binding (heat shock) proteins with ATPase activity that bind other cytoplasmic proteins and use the energy from ATP hydrolysis to prevent protein folding. 8. Proteins destined for mitochondria usually have two signal sequences. Why? Ans: One directs the protein into the matrix, the other to a sub-organelle space such as the intermembrane space, etc. 9. Using microsomes (MS) made from ER and other cytoplasmic components, mRNA, ribosomes, etc., describe a test tube experiment and results designed to test the signal hypothesis. Ans: Mix MS and ribosome-mRNA (coding for a protein with signal sequence)-SRP complex, etc. and radioactive amino acids. Test with protease to show is unavailable for degradation, i.e. it’s inside MS’s. 10. Where is COP II located and what is its role in protein trafficking?
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Ans: In the membrane of ER vesicles and facilitates their transport from ER to cis Golgi. 11. What is the function of α and β importin? Ans: Proteins that recognize proteins with NLS’s and facilitate their entry into nuclear pores. 12. What are SNARES and their role in protein trafficking? Ans: Complementary coil-coil proteins found on vesicles and target membrane that interact and aid in vesicle docking to the target membrane. 13. What are the major modifications to proteins passing through the ER and Golgi? Ans: Addition of normal and modified sugars with amine and acetyl groups. 14. What are lamins? Ans: intermediate filament protein that form the mechanical lattice or network under the inner nuclear membrane. 15. What are pulse chase experiments and how can they be used to determine the
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mcdb100finalquestans_08W - MCDB 100 Final Study Questions...

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