厦门大学细胞生物学2010年期中考试试题.doc

1.Glossary (20)1)Lipid raft (4)厦门大学细胞生物学课程试卷_学院_系_年级_专业主考老师： 试卷类型：（A 卷）2)Proteasome (4)3)Endomembrane system (4)4)Anoikis (4)5)Sorting signals (4)2、 What roles are cholesterol thought to play in our cell membranes? （8）3、Name the various types of coated protein involved in vesicular transport and expain their function respectively. (8)4、Describe the fate for an extracellular proteins that have been endocytosed (8)5、Summary the way that membrane protein associate with the lipid bilayer.(10)6、Identify several functions played by smooth endoplasmic reticulum. (8) 7、Explain the mechanism of asymmetrical distribution of various phospholipidsin the lipid bilayer of a cell.(10) 8、 Explain the physiological importance of Glycosylation（8）9、 Explain the mechanism for sorting lysosomal enzymes during the Vesiculartransport. (10)10、Describe the roles of the following in vesicular transport: A. SRP B.SignalSequence C. Bip (10)Answer:1. Glossary (20)（1）Lipid raft (4)A: Lipid rafts are membrane microdomains that are enriched in cholesterol andglycosphingolipids. They have been implicated in processes as diverse as signaltransduction, endocytosis and cholesterol trafficking.（2） Proteasome (4)A: Large protein complex in the cytosol with proteolytic activity that is responsiblefor degrading proteins that have been marked for destruction by ubiquitylation or bysome other means.（3）Endomembrane system (4)A: the structural and functional related intracellular membrane structures, includingEndoplasmic reticulum (ER),Golgi complex, lysosome, endosomes, secretory vesicles（4）Anoikis (4)A: a type of apoptosis that results from cell detachment from the extracellular matrix. （5）Sorting signals (4)A: Sorting signals are amino acid sequence that direct their delivery to targetinglocations.2. What roles are cholesterol thought to play in our cell membranes? （8）A: Cholesterol plays a important role in membrane mobility.(1).Interaction with the relatively rigid cholesterol decreases the mobility of hydrocarbon tails of phospholipids. (2) the presence of cholesterol in a phospholipid membrane interferes with closepacking of fatty acid tails in the crystalline state, and thus inhibits transition to thecrystal state (3) Phospholipid membranes with a high concentration of cholesterol have a fluidityintermediate between the liquid crystal and crystal states.3. Name the various types of coated protein involved in vesicular transport and expaintheir function respectively. (8)A: (A) Clathrin-coated vesicles: mediate transport from the Golgi apparatus tolysosome and from the plasma membrane to endosome.(B) COPI-coated vesicles: captures the escaped soluble ER resident proteins andcarries them in COPI-coated transport vesicles back to the ER. (C) COPII-coated vesicles: mediate transport from ER to Golgi apparatus 4. Describe the fate for a protein that have been endocytosed (8)A: (1) Recycling: proteins that are specifically retrieved are returned to the sameplasma membrane domain from which they came. (2) Transcytosis: proteins that are specifically retrieved are returned to adifferent domain of the plasma membrane (3) Degradation: proteins that are not specifically retrieved from endosomes are transported to lysosomes, where they are degraded.5. Summary the way that membrane protein associate with the lipid bilayer. (10)A: Most trans-membrane proteins are thought to extend across the bilayer as (1) asingle a helix , (2) as multiple a helices, or (3) as a rolled-upsheet. Some of thesesingle-pass and multipass proteins have a covalently attached fatty acid chaininserted in the cytosolic lipid monolayer (1). Other membrane proteins are exposed atonly one side of the membrane. (4) Some of these are anchored to the cytosolicsurface by an amphipathic a helix that partitions into the cytosolic monolayer of thelipid bilayer through the hydrophobic face of the helix. (5) Others are attached to thebilayer solely by a covalently attached lipid chain either a fatty acid chain or a prenylgroup in the cytosolic monolayer or, (6) via an oligosaccharide linker, tophosphatidylinositol in the noncytosolic monolayer.6. Identify several functions played by smooth endoplasmic reticulum. (8) A: (1) Synthesis of steroids in endocrine cells.(2) Detoxification of organic compounds in liver cells.(3) Sequestration of Ca2+. Ca2+-ATPase7. Explain the mechanism of asymmetrical distribution of various phospholipids in thelipid bilayer of a cell.(10) A: Asymmetrical distribution of various phospholipids in the lipid bilayer only occursin plasma membrane.（1）phospholipids synthesis takes place in the cytosolic leaflet of the ERmembrane.some of the newly formed phospholipid molecules are transferred from the cytosolic half of the ER bilayer to the lumenal leaflet by a phospholipidtranslocator called a scramblase.（2）The newly synthesized membrane is transported by vesicles from the ER toplasma membrane.（3）In plasma membrane, phospholipid translocators called flippases use theenergy of ATP hydrolysisto flip phosphatidylserine and phosphatidylethanolaminedirectionally from the extracellular to the cytosolic leaflet.Thus, the plasma membrane has a highly asymmetric distribution of phospholipids.8. Explain the physiological importance of Glycosylation（8）A: (1) Mark the State of Protein Folding (2) Limit the approach of other macromolecules to the protein surface, moreresistant to digestion by proteases. (3) Regulatory roles in signaling through the cell-surface receptor Notch, toallows these cells to respond selectively to activating stimuli.9. Explain the mechanism for sorting lysosomal enzymes during the Vesiculartransport. (10)A:（1）when lysosomal enzymes are transported from ER to cis Golgi network,lysosomal enzymes are covalently modified by phosphorylation to the terminalmannose residue to form mannose 6-phosphate (M6P) marker. Two enzymes actsequentially to catalyze the addition of M6P groups to lysosomal hydrolases. The firstis a GlcNAc phosphotransferase that specifically binds the hydrolase and addsGlcNAc-phosphate to one or two of the mannose residues on each oligosaccharidechain .A second enzyme,N-Acetylglucosaminidase, then cleaves off the GlcNAcresidue, leaving behind a newly created M6P marker. Since most lysosomalhydrolases contain multiple oligosaccharides, they acquire many M6P residues,providing a high affinity signal for the M6P receptor.(2) the lysosomal enzymes possessing the mannose 6-phophate(M6P) are recognizedand captured by M6P receptors in trans golgi network(TGN). (3) the lysosomal enzymes are enclosed in clathrin-coated vesicles and transported tolate endosomes in which the M6P receptors are dissociated and the phosphates areremoved from the lysosomal enzymes.(4) at last, the lysosomal enzymes are transported to lysosome.10. Describe the roles of the following in vesicular transport: A.SRP B.SignalSequence C.Bip (10)A.A:signal-recognition particle(SRP), which cycles between the ER membrane andthe cytosol and binds to the ER signal sequence, plays a role when secretoryproteins are synthesized in ER. The SRP binds to both the exposed ER signalsequence and the