中山大学《细胞生物学》思考题 00级细胞生物学思考题.doc

2000 级细胞生物学( 红色题分别为 03 细胞真题的实验设计和 04 细胞真题的最后一题) Testing & Thinking of cell biology Testing and Thinking(9-2-2002) 1. True or False. Identify each of the following statements as either true (T) or false (F). For each false statement, change the statement to make it true. (a) Oxygen, nitrogen, and carbon are the elements that most readily form strong multiple bonds. (b) Water has a higher heat of vaporization than most other liquids because of its high specific heat. (c) Oil droplets in water coalesce to form a separate phase because of the strong attraction of hydrophobic molecules for each other. (d) Ina hydrogen bond, electrons are shared between a hydrogen atom and two neighboring electronegative atoms. Answer: 1. (a) T (b) F; water has a higher heat of vaporization than most other liquids because of the hydrogen bonds that must be disrupted. (c) F; hydrophobic oil droplets in water coalesce not because of any intrinsic attraction of oil molecules for each other but because they have no affinity for polar molecules and therefore are not soluble in water. (d) T Testing and Thinking(9-4-2002) ECB2-16 B. Assume you were given a mixture consisting of one molecule each of all possible sequences ofa smallish protein of molecular weight 4800. How big a container would you need to hold this sample? Assume that the average molecular weight of an amino acid is 120. C. What does this calculation tell you about the fraction of possible proteins that are currently in use by anisms {the average molecular weight of proteins is about 30,000)? Answer(9-4-2002) protein with a molecular weight of 4800 is made of about 40 amino acids; thus there are × 10 52 (= 2040) different ways to make such a protein. Each individual protein molecule weighs 8× 10 -21g (= 4800/6 × 10 23 ); thus a mixture of one molecule each weighs 9× 10 31g (=8× 10 -21g× × 10 52 ), which is 15,000 times the total weight of the earth, 6× 10 24 kg. You would need a quite large container, ind