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Environmental Toxicology : Biological and Health Effects of Pollutants - Chapter 15

Đột biến là một quá trình mà hiến pháp di truyền của một tế bào bị thay đổi, cuối cùng dẫn đến một dân số biến đổi gen của các tế bào hoặc sinh vật. Mặc dù các đột biến có thể xảy ra trong các RNA của virus và DNA của bào quan tế bào chất, các đột biến quan tâm lớn nhất xảy ra trong gen trong nhân của tế bào. Cơ thể con người được ước tính có hơn 10 nghìn tỷ tế bào, và ở một số giai đoạn trong chu kỳ cuộc sống của mỗi. | Chapter 15 Mutagenic Pollutants 15.1 INTRODUCTION A mutation is a process by which the hereditary constitution of a cell is altered ultimately resulting in a genetically altered population of cells or organism. Although mutations can occur in the RNA of viruses and the DNA of cytoplasmic organelles the mutations of greatest interest occur within genes in the nucleus of the cell. The human body is estimated to contain more than 10 trillion cells and at some stage in its life cycle each cell contains a full complement of the genes needed by the entire organism. Genes composed of DNA in the nucleus of cells are clustered together in chromosomes. In the chromosomes of all but the most primitive organisms DNA is combined with protein. DNA the molecular basis of heredity in higher organisms is made up of a double helix held together by hydrogen bonds between purine and pyrimidine bases i.e. between adenine A and thymine T and between guanine G and cytosine C . Figure 15.1 shows the structures of the five bases in DNA and RNA and the pairing of bases in DNA is shown in Figure 15.2. The highly specific complementarity of these bases enables DNA to act as a template for its replication by DNA polymerases as well as the synthesis of RNA transcripts by RNA polymerases. For the information contained in DNA to be biologically expressed the sequence of the nucleotides in a gene is converted into the sequence of amino acids in a protein. It is the amino acid sequence that determines the enzymatic and structural properties of the protein thus formed. DNA clearly plays a pivotal role in the expression and perpetuation of life. However it is also a critical target for the action of many mutagenic environmental chemicals lesions in DNA may occur through the action of physical or chemical agents found in the environment. Occurrence of mutation however depends on the nature of the initial lesion and the response of cells to the DNA damage. If the damage is intermediate the mutations .