{"id":2004,"date":"2024-03-03T18:37:59","date_gmt":"2024-03-03T18:37:59","guid":{"rendered":"https:\/\/cake.appscodestudio.com\/?p=2004"},"modified":"2024-03-03T18:38:00","modified_gmt":"2024-03-03T18:38:00","slug":"structural-proteins","status":"publish","type":"post","link":"https:\/\/cake.appscodestudio.com\/index.php\/2024\/03\/03\/structural-proteins\/","title":{"rendered":"Structural proteins"},"content":{"rendered":"\n

Scleroproteins<\/a><\/h2>\n\n\n\n

Collagen<\/a><\/h2>\n\n\n\n

Collagen is the structural protein of\u00a0bones,\u00a0tendons,\u00a0ligaments, and\u00a0skin. For many years collagen was considered to be insoluble in\u00a0water. Part of the collagen of calf skin, however, can be extracted with citrate buffer at pH 3.7. A\u00a0precursor\u00a0of collagen called procollagen is converted in the body into collagen. Procollagen has a\u00a0molecular weight\u00a0of 120,000. Cleavage of one or a few\u00a0peptide\u00a0bonds of procollagen yields collagen, which has three subunits, each with a molecular weight of 95,000; therefore, the molecular weight of collagen is 285,000 (3 \u00d7 95,000). The three subunits are wound as spirals around an elongated straight axis. The length of each subunit is 2,900\u00a0angstroms, and its diameter is approximately 15 angstroms. The three chains are staggered, so that the trimer has no definite terminal limits.<\/p>\n\n\n\n

Collagen differs from all other proteins in its high content of\u00a0proline\u00a0and\u00a0hydroxyproline. Hydroxyproline does not occur in significant amounts in any other protein except elastin. Most of the proline in collagen is present in the sequence\u00a0glycine\u2013proline-X<\/em>, in which\u00a0X<\/em>\u00a0is frequently\u00a0alanine\u00a0or hydroxyproline. Collagen does not contain\u00a0cystine\u00a0or\u00a0tryptophan\u00a0and therefore cannot substitute for other proteins in the diet. The presence of proline causes kinks in the peptide chain and thus reduces the length of the\u00a0amino acid\u00a0unit from 3.7 angstroms in the extended chain of the \u03b2-structure to 2.86 angstroms in the collagen chain. In the\u00a0intertwined\u00a0triple helix, the glycines are inside, close to the axis; the prolines are outside.<\/p>\n\n\n\n

Native collagen resists the action of trypsin but is hydrolyzed by the bacterial\u00a0enzyme\u00a0collagenase. When collagen is boiled with water, the triple helix is destroyed, and the subunits are partially hydrolyzed; the product is\u00a0gelatin. The unfolded peptide chains of gelatin trap large amounts of water, resulting in a hydrated\u00a0molecule.<\/p>\n\n\n\n

When collagen is treated with\u00a0tannic acid\u00a0or with chromium salts,\u00a0cross links\u00a0form between the collagen fibres, and it becomes insoluble; the conversion of hide into leather is based on this tanning process. The tanned material is insoluble in hot water and cannot be\u00a0converted\u00a0to gelatin. On exposure to water at 62\u00b0 to 63\u00b0 C (144\u00b0 to 145\u00b0 F), however, the cross links formed by the tanning agents collapse, and the leather contracts irreversibly to about one-third its original volume.<\/p>\n\n\n\n

Collagen seems to undergo an aging process in living organisms that may be caused by the formation of cross links between collagen fibres. They are formed by the conversion of some lysine side chains to aldehydes (compounds with the general structure\u00a0R<\/em>CHO), and the combination of the\u00a0aldehydes\u00a0with the \u03b5-amino groups of intact lysine side chains. The protein\u00a0elastin, which occurs in the elastic fibres of\u00a0connective tissue, contains similar cross links and may result from the combination of collagen fibres with other proteins. When cross-linked collagen or elastin is\u00a0degraded, products of the cross-linked\u00a0lysine\u00a0fragments, called desmosins and isodesmosins, are formed.<\/p>\n","protected":false},"excerpt":{"rendered":"

Scleroproteins Collagen Collagen is the structural protein of\u00a0bones,\u00a0tendons,\u00a0ligaments, and\u00a0skin. For many years collagen was considered to be insoluble in\u00a0water. Part of the collagen of calf skin, however, can be extracted with citrate buffer at pH 3.7. A\u00a0precursor\u00a0of collagen called procollagen is converted in the body into collagen. Procollagen has a\u00a0molecular weight\u00a0of 120,000. Cleavage of one […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-2004","post","type-post","status-publish","format-standard","hentry","category-proteins"],"Cooking_time":"","jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/2004","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=2004"}],"version-history":[{"count":1,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/2004\/revisions"}],"predecessor-version":[{"id":2005,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/2004\/revisions\/2005"}],"wp:attachment":[{"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/media?parent=2004"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/categories?post=2004"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/tags?post=2004"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}