Figure 2\u201340. The X-ray diagram of the B-form of DNA (After Franklin and Gosling, 1953).
This diagram has played a definitive role in revealing the spatial structure of DNA. The
cross-like dark reflections prove that the structure is helical. The heavy black regions at the top and
bottom show that the purine and pyrimidine bases (3.4 nm thick) are regularly stacked next to
each other, perpendicular to the helical axis.<\/p>\n\n\n\n
image<\/p>\n\n\n\n
The three-dimensional models of the double DNA and RNA helices are \r\nshown in Figure 2\u201341 and the electron micrograph of a native portion of the \r\nDNA-molecule \u2014 in Figure 2\u201342. <\/pre>\n\n\n\nWith the discovery of the DNA double helix and the possibilities for
replication which such a helix renders, a lot of the problems of biology
and cytology were solved. It became clear what the chromosome
behaviour in the nucleus after the fertilization was due to, as well as the
nuclear division and observed even distribution in the process of
division. The phenomena of transformation, transduction and conjugation
which represent the transfer of hereditary material (DNA) from a donor
cell to a recipient cell found their explanation. The studies in that field
were spread on a large scale. A number of microorganisms became the
model objects for such a kind of study, such as bacteria, viruses,
microalgae, fungi, etc.
An important question arised: how the DNA replication is realized?
The answer was provided by Meselson and Stahl (1958). In experiments
with E. coli bacterial cultures using the method of the labelled atoms (\u00b9\u2074N
and \u00b9\u2075N) and centrifugation at a dense gradient of CsCl they have
established that DNA-replication is taking place in a semi-conservative
fashion (Fig. 2\u201343). This coincides with the hypothesis of Watson and
Crick, according to which the two initial complementary DNA-chains are
uncoiled and each serves as a template on which the new complementary
chain is synthesized (Fig. 2\u201344).<\/p>\n","protected":false},"excerpt":{"rendered":"Figure 2\u201340. The X-ray diagram of the B-form of DNA (After Franklin and Gosling, 1953).This diagram has played a definitive role in revealing the spatial structure of DNA. Thecross-like dark reflections prove that the structure is helical. The heavy black regions at the top andbottom show that the purine and pyrimidine bases (3.4 nm thick) […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"set","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[6],"tags":[],"class_list":["post-565","post","type-post","status-publish","format-standard","hentry","category-book"],"_links":{"self":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/565","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=565"}],"version-history":[{"count":1,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/565\/revisions"}],"predecessor-version":[{"id":612,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/565\/revisions\/612"}],"wp:attachment":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=565"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=565"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=565"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}