It is difficult to say when and at which stage of the evolutionary
development of cell the double nuclear membrane arises, which are the
reasons for that and the mode of realization. These questions are of vital
importance, since they are directly related to the elucidation in principle of the
ways of realizing the structural organization of cells \u2014 by the way of
compartmentalization or that of endosymbiosis (see Chapter 2, Section 2.10).
Already prevailing is the concept that the \u201cenergetic\u201d organelles of
eukaryotic cells \u2014 chloroplasts and mitochondria, which also possess
double membrane and its own DNA, before have been independently
existed prokaryotes and have been integrated into a common biosystem.
On these grounds some authors suggest the idea of endosymbiotic origin
also of the cell nucleus. In his review Geyer (1980) analyzes 34 randomly
selected textbooks, monographs and scientific papers from 1893 to 1979.
In 6 of them the nucleus is classified as an organelle, in 8 it is not
considered to be organelle, in 14 it is shown as compartment and in 6 there
is a lack of definite classification. The author is of the opinion that cell
nucleus is a compartment without relying on any evidence. This idea is very
abstract, to a great extent unacceptable, but it deserves attention.
As it was already mentioned in every nucleus of eukaryotic cells there
are one, and in some cases two or more nucleoli. These, usually spherical
small bodies (see Fig. 2\u201359) are easily observed in light or electron
microscope, when the cells are not in mitosis. During metaphase the
nucleolus visibly disappear and appear again in telophase, and acquire its
real shape and dimensions in the newly formed daughter cells. Its
characteristic peculiarities are the compact consistence and a changeability
regarding morphology and chemical composition, which is related with the
functions performed in the cell.
Some details of nucleolus structure were elucidated by means of
electron microscopy. In contrast to the basic cell organelles the nucleolus
lacks double membrane. It is an intranuclear organoid considered to be the
place of synthesis and assembly of ribosomal subunits.
The most important component of the cell nucleus is the chromatin, in
which composition DNA also participates. During mitosis the chromatin is
organized as chromosomes. They form the genome of cell, where the
whole history of its evolution is written. According to Bernal (1969) \u201cthe
nucleus is of programming importance. It keeps the keys of the past and
the future, near and more distant. The cytoplasm, in contrast to the
nucleus, is related with the present. It provides what is needed at the
present moment and its reactions are immediate\u201d.<\/p>\n","protected":false},"excerpt":{"rendered":"
It is difficult to say when and at which stage of the evolutionarydevelopment of cell the double nuclear membrane arises, which are thereasons for that and the mode of realization. These questions are of vitalimportance, since they are directly related to the elucidation in principle of theways of realizing the structural organization of cells \u2014 […]<\/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-790","post","type-post","status-publish","format-standard","hentry","category-book"],"_links":{"self":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/790","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=790"}],"version-history":[{"count":1,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/790\/revisions"}],"predecessor-version":[{"id":799,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/790\/revisions\/799"}],"wp:attachment":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=790"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=790"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=790"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}