Every living cell contains, in addition to\u00a0water\u00a0and salts or minerals, a large number of\u00a0organic compounds, substances composed of\u00a0carbon\u00a0combined with varying amounts of\u00a0hydrogen\u00a0and usually also of\u00a0oxygen.\u00a0Nitrogen,\u00a0phosphorus, and\u00a0sulfur\u00a0are likewise common\u00a0constituents. In general, the bulk of the organic matter of a cell may be classified as (1)\u00a0protein, (2)\u00a0carbohydrate, and (3)\u00a0fat, or\u00a0lipid. Nucleic acids and various other organic derivatives are also important constituents. Each class contains a great\u00a0diversity\u00a0of individual\u00a0compounds. Many substances that cannot be classified in any of the above categories also occur, though usually not in large amounts.<\/p>\n\n\n\n
Proteins are fundamental to life, not only as structural elements (e.g., collagen) and to provide defense (as antibodies) against invading destructive forces but also because the essential biocatalysts are proteins. The\u00a0chemistry\u00a0of proteins is based on the researches of the German chemist\u00a0Emil Fischer, whose work from 1882 demonstrated that proteins are very large molecules, or polymers, built up of about 24\u00a0amino acids. Proteins may vary in size from small\u2014insulin\u00a0with a\u00a0molecular weight\u00a0of 5,700 (based on the weight of a hydrogen atom as 1)\u2014to very large\u2014molecules with molecular weights of more than 1,000,000. The first complete amino acid sequence was determined for the insulin\u00a0molecule\u00a0in the 1950s. By 1963 the chain of amino acids in the protein\u00a0enzyme\u00a0ribonuclease (molecular weight 12,700) had also been determined, aided by the powerful physical techniques of X-ray-diffraction analysis. In the 1960s,\u00a0Nobel Prize\u00a0winners\u00a0J.C. Kendrew\u00a0and\u00a0M.F. Perutz, utilizing X-ray studies, constructed detailed atomic models of the proteins\u00a0hemoglobin\u00a0and\u00a0myoglobin\u00a0(the respiratory pigment in muscle), which were later confirmed by sophisticated chemical studies. The\u00a0abiding\u00a0interest of biochemists in the structure of proteins rests on the fact that the arrangement of chemical groups in space yields important clues regarding the biological activity of molecules.<\/p>\n\n\n\n
Carbohydrates\u00a0include such substances as sugars,\u00a0starch, and\u00a0cellulose. The second quarter of the 20th century witnessed a striking advance in the knowledge of how living cells handle small molecules, including carbohydrates. The metabolism of carbohydrates became clarified during this period, and elaborate pathways of carbohydrate breakdown and subsequent storage and utilization were gradually outlined in terms of cycles (e.g., the Embden\u2013Meyerhof glycolytic cycle and the Krebs cycle). The involvement of carbohydrates in respiration and muscle contraction was well worked out by the 1950s. Refinements of the schemes continue.<\/p>\n\n\n\n
Fats, or\u00a0lipids,\u00a0constitute\u00a0a\u00a0heterogeneous\u00a0group of organic chemicals that can be extracted from biological material by nonpolar solvents such as\u00a0ethanol,\u00a0ether, and benzene. The classic work concerning the formation of body fat from carbohydrates was accomplished during the early 1850s. Those studies, and later confirmatory evidence, have shown that the conversion of carbohydrate to fat occurs continuously in the body. The\u00a0liver\u00a0is the main site of fat metabolism. Fat absorption in the intestine was studied as early as the 1930s. The control of fat absorption is known to depend upon a combination action of secretions of the\u00a0pancreas\u00a0and bile salts. Abnormalities of fat metabolism, which result in disorders such as obesity and rare clinical conditions, are the subject of much biochemical research. Equally interesting to biochemists is the association between high levels of fat in the blood and the occurrence of\u00a0arteriosclerosis\u00a0(\u201chardening\u201d of the arteries).<\/p>\n\n\n\n
Nucleic acids are large, complex compounds of very high molecular weight present in the cells of all organisms and in viruses. They are of great importance in the\u00a0synthesis\u00a0of proteins and in the transmission of hereditary information from one generation to the next. Originally discovered as constituents of cell nuclei (hence their name), it was assumed for many years after their isolation in 1869 that they were found nowhere else. This assumption was not challenged seriously until the 1940s, when it was determined that two kinds of\u00a0nucleic acid\u00a0exist:\u00a0deoxyribonucleic acid\u00a0(DNA), in the nuclei of all cells and in some viruses; and ribonucleic acid (RNA), in the cytoplasm of all cells and in most viruses.<\/p>\n\n\n\n
The profound biological significance of nucleic acids came gradually to light during the 1940s and 1950s. Attention turned to the mechanism by which\u00a0protein synthesis\u00a0and genetic\u00a0transmission\u00a0was controlled by nucleic acids (see below\u00a0Genes). During the 1960s, experiments were aimed at refinements of the\u00a0genetic code. Promising attempts were made during the late 1960s and early 1970s to accomplish duplication of the molecules of nucleic acids outside the cell\u2014i.e., in the laboratory. By the mid-1980s\u00a0genetic engineering\u00a0techniques had accomplished, among other things,\u00a0in vitro fertilization\u00a0and the recombination of DNA (so-called\u00a0gene\u00a0splicing).<\/p>\n","protected":false},"excerpt":{"rendered":"
Every living cell contains, in addition to\u00a0water\u00a0and salts or minerals, a large number of\u00a0organic compounds, substances composed of\u00a0carbon\u00a0combined with varying amounts of\u00a0hydrogen\u00a0and usually also of\u00a0oxygen.\u00a0Nitrogen,\u00a0phosphorus, and\u00a0sulfur\u00a0are likewise common\u00a0constituents. In general, the bulk of the organic matter of a cell may be classified as (1)\u00a0protein, (2)\u00a0carbohydrate, and (3)\u00a0fat, or\u00a0lipid. Nucleic acids and various other organic derivatives […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12],"tags":[],"class_list":["post-2040","post","type-post","status-publish","format-standard","hentry","category-biochemistry"],"Cooking_time":"","jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/2040","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/comments?post=2040"}],"version-history":[{"count":1,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/2040\/revisions"}],"predecessor-version":[{"id":2041,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/2040\/revisions\/2041"}],"wp:attachment":[{"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/media?parent=2040"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/categories?post=2040"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/tags?post=2040"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}