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1、2022年考博英语-中国科学技术大学考前提分综合测验卷（附带答案及详解）1. 单选题Protein synthesis begins when the gene encoding a protein is activated. The genes sequence of nucleotides is transcribed into a molecule of messenger RNA (mRNA), which reproduces the information contained in that sequence. Transported outside the nucleus to
2、the cytoplasm, the mRNA is translated into the protein it encodes by an organelle known as a ribosome, which strings together amino acids in the order specified by the sequence of elements in the mRNA molecule. Since the amount of mRNA in a cell determines the amount of the corresponding protein, fa
3、ctors affecting the abundance of mRNAs play a major part in the normal functioning of a cell by appropriately regulating protein synthesis. For example, an excess of certain proteins can cause cells to proliferate abnormally and become cancerous; a lack of the protein insulin results in diabetes.Bio
4、logists once assumed that the variable rates at which cells synthesize different mRNAs determines the quantities of mRNAs and their corresponding proteins in a cell. However, recent investigations have shown that the concentrations of most mRNAs correlate best, not with their synthesis rate, but rat
5、her with the equally variable rates at which cells degrade the different mRNAs in their cytoplasm. If a cell degrades both a rapidly and a slowly synthesized mRNA slowly, both mRNAs will accumulate to high levels.An important example of this phenomenon is the development of red blood cells from thei
6、r unspecialized parent cells in bone marrow. For red blood cells to accumulate sufficient concentrations of hemoglobin (which transports oxygen) to carry out their main function, the cells parent cells must simultaneously produce more of the constituent proteins of hemoglobin and less of most other
7、proteins. To do this, the parent cells halt synthesis of non-hemoglobin mRNAs in the nucleus and rapidly degrade copies of the non-hemoglobin mRNAs remaining in the cytoplasm. Halting synthesis of mRNA alone would not affect the quantities of proteins synthesized by the mRNAs still existing in the c
8、ytoplasm. Biologists now believe that most cells can regulate protein production most efficiently by varying both mRNA synthesis and degradation, as developing red cells do, rather than by just varying one or the other.1. The passage is primarily concerned with discussing the _.2. According to the p
9、assage, which of the following can happen when, protein is not appropriately regulated?3. The accumulation of concentrations of hemoglobin in red blood cells is mentioned in the passage as an example of which of the following?4. Which of the following best describes the relationship between the seco
10、nd and third paragraphs of the passage?问题1选项A.influence of mRNA concentrations on the development of red blood cellsB.role of the synthesis and degradation of mRNA in cell functioningC.mechanism by which genes are transcribed into mRNAD.differences in mRNA concentrations in cell nuclei and in the cy
11、toplasm问题2选项A.Diabetes can result from errors that occur when the ribosomes translate mRNA into protein.B.A deficiency of red blood cells can occur if bone marrow cells produce too much mechanism.C.Cancer can result from an excess of certain proteins and diabetes can result from an insulin deficienc
12、y.D.Excessive synthesis of one protein can trigger increased degradation of mRNAs for other proteins and create severe protein imbalances.问题3选项A.The effectiveness of simultaneous variation of the rates of synthesis and degradation of mRNAB.The role of the ribosome in enabling a parent cell to develo
13、p properly into a more specialized form.C.The importance of activating the genes for particular proteins at the correct moment.D.The kind of evidence for support of a view of mRNA synthesis that is now considered obsolete.问题4选项A.The second paragraph presents arguments in support of a new theory and
14、the third paragraph presents arguments against that theory.B.The second paragraph describes a traditional view and the third paragraph describes the view that has replaced it on the basis of recent investigations.C.The third paragraph describes an investigation that was undertaken to resolve problem
15、s described in the second paragraph.D.The third paragraph describes a specific case of a phenomenon that is described generally in the second paragraph.【答案】第1题:B第2题:C第3题:A第4题:D【解析】第1题:【选项释义】The passage is primarily concerned with discussing the _. 本文主要讨论了_。A. influence of mRNA concentrations on the
16、development of red blood cells A. 信使核糖核苷酸浓度对红细胞发育的影响B. role of the synthesis and degradation of mRNA in cell functioning B. 信使核糖核苷酸的合成和降解在细胞功能中的作用C. mechanism by which genes are transcribed into mRNA C. 基因被转换成信使核糖核苷酸的机制D. differences in mRNA concentrations in cell nuclei and in the cytoplasm D. 细胞核和细胞质中信使核糖核苷酸浓度的差异【答案
