记的胰岛素竞争质膜受体。通过检测放射性即式丙酮酸;⑤动力势(协同) 可证明 2. What is the advantage of having extracellular signal transmitt 六、分析、计算与思考(20分) by a cascade of sequential events? 1.“解铃还需系铃人”这句谚语在细胞活动中 Answer②: Transduction of an extracellular 能找到对应的故事吗?请 signal via a cascade of sequential event advantageous because of 说明。(5分) amplification of the signal. the binding 答:IP的钙的释放和对钙浓度的消减。 of a few molecules to a receptor can result in the synthesis of a large number of 2.计算题(5分) effector molecules because at each step of the cascade the signal is enzymatically O The average molecular weight of prote ins in amplified the cell is about 30.000 daltons. A few proteins, however, are very much larger. The largest known 3. Heating of calf type I collagen fiber polypeptide chain made by any cell is a to 45c denatures the triple helices and protein called titin(made separates the three chains from each other. by muscle cells ), and it has a molecular Collagen that has been treated in this way eight of 3, 000,000 daltons does not renature to form a normal collagen Estimate how long it will take a muscle cell to translate an mRNA coding triple helix. Why? for titin (assume the average molecular Answer The N-terminal and C-terminal weight of an amino acid to be 120 propeptides pre-sent in newly synthesized and a translation rate of two amino acids per collagen monomers as-ist in alignment of second for eucaryotic cells) the peptides to form the triple helix 2 Transcription occurs at a rate of about 30 These propeptides are removed after the trimers nucleotides per second. Is it transported to the possible to calculate the time required to extracellular mat and thus are not synthesize a titin mRNA from available to perform the same function in the information denatured calf type I collagen. In addition, inappropriate disulfide bridges 2. Answer: can be generated during renaturation O A titin molecule is made of 25,000 amino these will also inhibit the generation of acids. It therefore takes about a normal triple helix 3.5 hours to synthesize a single molecule of titin in muscle cells (2 To calculate the time it takes to transcribe a titin mRNA, you would need to know the size of its gene, which is likely to contain many Introns Transcription of the exons alone requires about 42 minutes. Because n be quite large, the time require to transcribe the entire gene is likely to be considerably longer. 2.综合思考(10分按答题最多者计算每题得 分) ①物质运输是一个耗能过程,请举例说明有 哪些能量来源? 答∶①自由能;②ATP;③光能;④磷酸烯醇8 记的胰岛素竞争质膜受体。通过检测放射性即 可证明。 六、分析、计算与思考(20 分) 1. “解铃还需系铃人”这句谚语在细胞活动中 能找到对应的故事吗？请 说明。（5 分） 答：IP3 的钙的释放和对钙浓度的消减。 2. 计算题（5 分） ① The average molecular weight of proteins in the cell is about 30,000 daltons. A few proteins, however, are very much larger. The largest known polypeptide chain made by any cell is a protein called titin (made by muscle cells), and it has a molecular weight of 3,000,000 daltons. Estimate how long it will take a muscle cell to translate an mRNA coding for titin (assume the average molecular weight of an amino acid to be 120, and a translation rate of two amino acids per second for eucaryotic cells). ② Transcription occurs at a rate of about 30 nucleotides per second. Is it possible to calculate the time required to synthesize a titin mRNA from the information given here? 2. Answer: ① A titin molecule is made of 25,000 amino acids. It therefore takes about 3.5 hours to synthesize a single molecule of titin in muscle cells. ② To calculate the time it takes to transcribe a titin mRNA, you would need to know the size of its gene, which is likely to contain many introns. Transcription of the exons alone requires about 42 minutes. Because introns can be quite large, the time required to transcribe the entire gene is likely to be considerably longer. 2. 综合思考(10分, 按答题最多者计算每题得 分) ① 物质运输是一个耗能过程，请举例说明有 哪些能量来源？ 答：①自由能；②ATP；③光能；④磷酸烯醇 式丙酮酸；⑤动力势（协同） ②． What is the advantage of having an extracellular signal transmitted by a cascade of sequential events? Answer②:Transduction of an extracellular signal via a cascade of sequential events is advantageous because of the amplification of the signal. The binding of a few molecules to a receptor can result in the synthesis of a large number of effector molecules because at each step of the cascade the signal is enzymatically amplified. ③． Heating of calf type I collagen fibers to 450 C denatures the triple helices and separates the three chains from each other. Collagen that has been treated in this way does not renature to form a normal collagen triple helix. Why? Answer ③ The N-terminal and C-terminal propeptides pre-sent in newly synthesized collagen monomers as-ist in alignment of the peptides to form the triple helix. These propeptides are removed after the trimers are transported to the extracellular matrix, and thus are not available to perform the same function in denatured calf type I collagen. In addition, inappropriate disulfide bridges can be generated during renaturation; these will also inhibit the generation of a normal triple helix