{"id":853,"date":"2023-12-11T22:51:08","date_gmt":"2023-12-11T22:51:08","guid":{"rendered":"https:\/\/cellandcelldivision.com\/?p=853"},"modified":"2023-12-11T22:51:09","modified_gmt":"2023-12-11T22:51:09","slug":"page-209","status":"publish","type":"post","link":"https:\/\/cellandcelldivision.com\/?p=853","title":{"rendered":"Page 209"},"content":{"rendered":"\n

Still unclear are the reasons for the transition of the cells from the
restriction point R to G\u2081 -phase, i.e. to a new cell division. According to one
of the existing hypotheses there is a necessity of accumulating certain
amount of unstable (trigger) proteins<\/strong>. This supposition is based on data
that their highest content is observed only in phase G1 (Pardee et al., 1978;
Rossow et al., 1979).
Cell division can also be controlled by a number of mechanisms
operating on the feedback principle. These mechanisms are of special
importance, since they limit the uncontrolled accumulation of cells in
individual tissues or organs that can lead to lethal consequences for the
given organism, as it is in the tumour formations. This is most clearly
expressed in animal tissues and organs. For instance, in a state of repose
liver cells begin to divide rapidly after separating a part of this organ and
stop the dividing, when the mass reaches the normal status. Epithelial
mammalian cells, developing in a cell culture on a solid nutrient medium,
also stop the dividing when there is no vacant place for them. This
phenomenon has termed contact retention <\/strong>(Folkman, Moskona, 1978).
Cell division can be caused not only when there is a vacant place for
their growth, but also when they are in a suitable encirclement. In the
multilayer skin epidermis division is observed in only one of the basal cell
layers located on the basal membrane, separating them from the derm. If
the basal cells are located deeper into the derm or above it and have lost
the contact with the basal membrane, they stop to divide. That is explained
with the presence of so-called position signals<\/strong> (Rutter et al., 1973; French
et al., 1976; Bryant et al., 1977, etc.) for which a little is known up to now. It
is assumed that they are realized by means of a number of growth factors
like specific proteins, small molecules of peptide or steroid character,
hormones circulating in blood or substances operating within short
distances \u2014 local chemical mediators<\/strong>.
The control and realization of cell division is a complex process.
Undoubtedly it includes different mechanisms, the genetic material and a
number of specific proteins. Some of them were already mentioned, and
possibly there are still unknown ones. Recently the attention was attracted
by a protein widely spread in all living cells \u2014 so-called ubiquitin<\/strong> (from
Latin ubique<\/em> \u2014 everywhere, all over). According to Bradbury et al. (1981) in
mammal tissues ubiquitin participates with 2\u20143% of the amount of
conservative histones. This is a very stable globular protein. The discovery
of bifurcate protein A24, consisting of ubiquitin covalently bound with
histone H2A, is the first direct proof of the role of ubiquitin in chromatin
structure and functions.
\u201cResearchers once expected \u2014 noted Barinaga (1995) \u2014 that the cell
cycle to be regulated mainly by the well-timed production of regulatory
proteins. But today one of the hottest topics in the cell-cycle field deals with<\/p>\n","protected":false},"excerpt":{"rendered":"

Still unclear are the reasons for the transition of the cells from therestriction point R to G\u2081 -phase, i.e. to a new cell division. According to oneof the existing hypotheses there is a necessity of accumulating certainamount of unstable (trigger) proteins. This supposition is based on datathat their highest content is observed only in phase […]<\/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-853","post","type-post","status-publish","format-standard","hentry","category-book"],"_links":{"self":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/853","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=853"}],"version-history":[{"count":1,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/853\/revisions"}],"predecessor-version":[{"id":860,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/853\/revisions\/860"}],"wp:attachment":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=853"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=853"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=853"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}