Читать книгу Abnormal Psychology - William J. Ray - Страница 98

With the discovery of the structure of DNA by Watson and Crick in 1953, specifying the method by which genetic material was copied became possible. Deoxyribonucleic acid (DNA) provides information necessary to produce proteins. Proteins can be viewed as a link between the genotype (complete genetic composition of an organism) and the phenotype (an organism’s observable characteristics). Moving the genotype to the phenotype initially begins in two steps. First, the information in DNA is encoded in ribonucleic acid (RNA). Second, this information in RNA determines the sequence of amino acids, which are the building blocks of proteins. Technically, the DNA synthesis of RNA is called transcription, whereas the step from RNA to protein is called translation. RNA is like DNA except its structure is a single strand, whereas DNA has a double strand. Once encoded, the RNA goes to a part of the cell capable of producing proteins. Proteins are produced by putting together amino acids.

deoxyribonucleic acid (DNA): a molecule that provides information necessary to produce proteins, which are involved in growth and functioning

genotype: the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment

phenotype: an organism’s observable characteristics

ribonucleic acid (RNA): DNA information is carried as RNA, which determines the sequence of amino acids, the building blocks of proteins; it is made up of single strands rather than the dual strands in DNA

To be more specific, DNA represents the chemical building blocks, or nucleotides, that store information. There are only four types of bases for this coding. DNA molecules are composed of two strands that twist together in a spiral manner. The strands consist of a sugar phosphate backbone to which the bases are attached. Each strand consists of four types of nucleotides that are the same except for one component, a nitrogen-containing base. The four bases are adenine, guanine, thymine, and cytosine. These are generally referred to as A, G, T, and C. To give you some sense of size, each full twist of the DNA double helix is 3.4 nanometers (i.e., one billionth of a meter). Said in other terms, if we took the DNA in the 46 chromosomes of a single human cell and stretched it out, it would be around 6 feet long. This measurement gives you some idea of the thinness of DNA.

DNA, which is the information storage molecule, transfers information to RNA, which is the information transfer molecule, to produce a particular protein. Further, change in the rate at which RNA is transcribed controls the rate at which genes produce proteins. The expression rate of different genes in the same genome may vary from 0 to approximately 100,000 proteins per second. Thus, not only do genes produce proteins, but they do so at different rates. The crucial question becomes what causes a gene to turn on or off.

Genome is the name given to the complete set of genes in a given cell. The Human Genome Project was started in 1990 by the United States with the goal of mapping all the genes of the human body. It was an international project that was declared complete in 2003. The estimation at that time was that there are approximately 20,500 genes in a human cell.