In 1953\u00a0James D. Watson\u00a0and\u00a0Francis H.C. Crick\u00a0proposed a three-dimensional structure for DNA based on low-resolution X-ray crystallographic\u00a0data\u00a0and on Erwin Chargaff\u2019s observation that, in naturally occurring DNA, the amount of T equals the amount of A and the amount of G equals the amount of C. Watson and Crick, who shared a\u00a0Nobel Prize\u00a0in 1962 for their efforts, postulated that two strands of polynucleotides coil around each other, forming a\u00a0double helix. The two strands, though identical, run in opposite directions as determined by the orientation of the 5\u2032 to 3\u2032 phosphodiester bond. The sugar-phosphate chains run along the outside of the helix, and the bases lie on the inside, where they are linked to\u00a0complementary\u00a0bases on the other strand through hydrogen bonds.<\/p>\n\n\n\n
The double helical structure of normal DNA takes a right-handed form called the B-helix. The helix makes one complete turn approximately every 10 base pairs. B-DNA has two principal grooves, a wide major groove and a narrow minor groove. Many proteins interact in the space of the major groove, where they make sequence-specific contacts with the bases. In addition, a few proteins are known to make contacts via the minor groove.<\/p>\n\n\n\n
Several structural variants of DNA are known. In\u00a0A-DNA, which forms under conditions of high\u00a0salt\u00a0concentration and minimal water, the base pairs are tilted and displaced toward the minor groove. Left-handed\u00a0Z-DNA forms most readily in strands that contain sequences with alternating purines and pyrimidines. DNA can form triple helices when two strands containing runs of pyrimidines interact with a third strand containing a run of purines.<\/p>\n\n\n\n
B-DNA is generally depicted as a smooth helix; however, specific sequences of bases can distort the otherwise regular structure. For example, short tracts of A residues interspersed with short sections of general sequence result in a bent DNA molecule. Inverted base sequences, on the other hand, produce cruciform structures with four-way junctions that are similar to recombination intermediates. Most of these\u00a0alternative\u00a0DNA structures have only been characterized in the laboratory, and their cellular significance is unknown.<\/p>\n","protected":false},"excerpt":{"rendered":"
In 1953\u00a0James D. Watson\u00a0and\u00a0Francis H.C. Crick\u00a0proposed a three-dimensional structure for DNA based on low-resolution X-ray crystallographic\u00a0data\u00a0and on Erwin Chargaff\u2019s observation that, in naturally occurring DNA, the amount of T equals the amount of A and the amount of G equals the amount of C. Watson and Crick, who shared a\u00a0Nobel Prize\u00a0in 1962 for their efforts, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[],"class_list":["post-1852","post","type-post","status-publish","format-standard","hentry","category-nucleic-acids"],"Cooking_time":"","jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1852","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=1852"}],"version-history":[{"count":1,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1852\/revisions"}],"predecessor-version":[{"id":1853,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1852\/revisions\/1853"}],"wp:attachment":[{"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/media?parent=1852"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/categories?post=1852"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cake.appscodestudio.com\/index.php\/wp-json\/wp\/v2\/tags?post=1852"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}