职称英语考试

【单选题】TheCentralDogmaThough it comes as no surprise that the composition ofDN
A、between different organisms is different, it is not immediately obvious why the muscle cells, blood cells, and brain cells of any one particular vertebrate(脊椎动物) are so different in their structure and composition when theDN
A、of every one of their cells is identical. This is the key to one of the most exciting areas of modern cell biology. In different cell types, different sets of the total number of genes (genome) (基因组) are expresse
D、In other words, different regions of theDN
A、are "active" in the muscle cells, blood cells, and brain cells.To understand how this difference inDN
A、activity can lead to differences in cell structure and composition, it is necessary to consider what is often known as the central dogma(法则) of molecular biology: "DN
A、makes RN
A、make protein. " In molecular terms, a gene is that portion ofDN
A、that encodes for a single protein. The dictum" one gene makes one protein" has required some modification(改变) with the discovery that some proteins are composed of several different polypeptide(多肽) chains, but the "one gene makes one polypeptide" rule does hol
D、DN
A、Contains theBlueprint forAllCell Proteins.Messenger RN
A、is a precise copy (transcript) of the coded sequence of nucleic acid bases inDNA, and this message is translated into a unique protein molecule on specialist organelles (ribo-somes) present in the cytoplasm(细胞质) of all cells. Proteins(蛋白质), which are largely made up of carbonC、,hydrogen(H), oxygen(O) ,and nitrogen(N) ,are constructed from 20 different, common amino acids. The versatility of proteins, the workhorse molecules of the cell, stems from the immense variety of molecular shapes that can be created, by linking amino acids together in different sequences. The smaller proteins consist of only a few dozen amino acids, whereas the larger ones may contain in excess of 200 amino acids, all linked together in a linear(线状的) chain by peptide bonds. As the proteins are released from the ribosome(核糖体) ,they fold into unique shapes, under the influence of chemical forces that depend on the particular sequence of amino acids. So the protein primary sequence , encoded in the gene and faithfully transcribed and translated into an amino acid chain, determines the three-dimensional structure of the emerging molecule. The human body possesses some 30 000 different kinds of proteins and several million copies of many of these.Each plays a specific role——for example, hemoglobin carries oxygen in the blood, actin(肌动蛋白) and myosin(肌球蛋白) interact to generate muscle movement, and acetylcholine (乙酸胆碱) receptor molecules mediate chemical transmission between nerve and muscle cells. Enzymes—ProteinBiocatalysts An essential group of proteins—the enzymes (酵素)—act as biological catalysts (催化剂) and regulate all aspects of cell metabolism (新陈代谢). They enable breakdown of high-energy food molecules (carbohydrates) to provide energy for biological reactions, and they control the synthetic pathways that result in the generation of lipids(e.g., fats, cholesterol(胆固醇), and other vital membrane(膜) components), carbohydrates (碳水化合物) (sugars, starch (淀粉) , and cellulose (纤维素) , the key components of plant cell walls) ,and many vital small biomolecules essential for cell function. Which of the following statements about the central dogma is false
A、The central dogma could be expressed asDN
A、makes RN
A、make Protein."
B．Each protein contains only one gene.
C．Each polypeptide contains only one gene.

D、The central dogma is the key to understand how the difference inDN
A、activity can lead to the difference in cell structure and composition.

网考网参考答案：B
网考网解析：
A)中心法则可以表述为“DNA制造RNA制造了蛋白质”。这是文中的原话，故该陈述正确。C)每种多肽包含一种基因。这句陈述正确。D)中心法则是理解DNA活动的差异可导致细胞结构与组成的不同的钥匙。这句陈述正确。B)每一蛋白质仅包含一种基因。这句陈述错误，故B)为正确选项。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>