课程名称︰细胞生物学 课程性质︰必修 课程教师︰沈汤龙 开课学院：植微系 开课系所︰生农院 考试日期（年月日）︰2018/06/28 14:20-16:20 考试时限（分钟）：120分钟 试题 : 01. Actin filiments are a major element of the cytoskeleton. The cytoskeleton provides a framework for the cell and acts as a scaffold that both determines cell shape and positions organelles within cells. For example, the cytoskeleton provides the tracks along which organelles move. At the same time, the cytoskeleton is subject to cleavage by proteins like ADF/cofilin. What is the apparent function of ADF/cofilin? 02. How does Ca2+ molecularly regulate the activity of myosin motors? 03. According to the generally accepted fluid mosaic model of membrane structure, membranes are two-dimensional fluids through which proteins can move freely in lateral directions. Provide an example of a membrane protein that is not free to move laterally within a plasma membrane. 04. How does the plasma membrane come to be hyperpolarized locally during action potential reversal? 05. How is proline hydroxylation in collagen encoded in the genome? What is the relationship between this encoding mechanism and scurvy? 06. Unlike polysaccharides such as glycogen or cellulose, glycosaminoglycans(GAGs) are highly negaively charged. What is the sourse and function of this negative charge? 07. Growth factors and cytokines both lead to tyrosine phosphorylation through receptors, but they do so through different mechanisms. What is the key difference between the receptors for these two classes of ligands in terms of their tyrosine kinase activity? 08. As a cell biologist for a pharmaceutical company, you are charged with developing a drug to inhibit the cAMP-cAMP response element binding protein (CREB) pathway. Briefly describe the cascade leading to CREB activation and where one might target a drug to block its activation. 09. What are three cellular processes in which the Ras/Raf/MAP kinase pathway is activated? 10. During G2 the Wee1 protein phosphorylates tyrosine-15 of the Cdc2 protein kinase, thus inactivating it. Only once dephosphorylation occurs and Cdc2 becomes active can the cell pass from G2 into M and proceed to cell division. Can you think of a reason why the Weelprotein was named as such? 11. Why is Rb, a product of the retinoblastoma gene, now termed a member of a family of proteins designated tumor suppressor genes? 12. One of the hallmark characteristics of apoptosis is fragmentation of nuclear DNA. Which protein is responsible for this fragmentation, and what is the mechanism by which it degrades the DNA? 13. Bcl-2 is an antiapoptotic protein which, under normal conditions, contributes to the balance of acivity of numerous proapoptotic and antiapoptotic proteins. What would be the result of a gain-of-function mutation in the bcl-2 gene that led to constant and significant elevation in cellular Bcl-2 protein levels? 14. Signaling pathways mediate many cellular processes, as explained in Chapter 15. Apoptosis is also regulated by multiple signaling pathways. Breifly describe two signaling pathways that regulate apoptosis. 15. Cellular transformation from normal to tumor cells is a hallmark of cancer. The focus assay represents the first and most widely used assay to assess cell transformation. Describe the focus assay. 16. How does adenoviral E1A:Rb lead to excessive cell proliferation following viral infection? 17. Describe how the first oncogene was discovered. 18. Please list 2 examples of stem cells in maintaining the homeostasis of the corresponding physiology. --

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