{"id":782,"date":"2023-12-07T20:54:50","date_gmt":"2023-12-07T20:54:50","guid":{"rendered":"https:\/\/cellandcelldivision.com\/?p=782"},"modified":"2023-12-07T20:54:51","modified_gmt":"2023-12-07T20:54:51","slug":"page-181","status":"publish","type":"post","link":"https:\/\/cellandcelldivision.com\/?p=782","title":{"rendered":"Page 181"},"content":{"rendered":"\n

described it as areola usually more dark than the cell envelope, without
giving any picture. The term nucleus<\/strong> has been introduced by G. Valentin
(1836), who for the first time has described the nucleolus located in it. The
presence of nucleus in each cell has served as a leading idea for the
creating of cell theory by M. Schleiden and Th. Schwann.
At present, the nucleus is considered to be obligatory and irreversible
composite organelle of each eukaryotic cell. This concept has been
appreciated in view of the fact that a cell without nucleus cannot develop
normally and, what is most important, cannot reproduce. Cases are known,
where during a large part of the period of its existence the cells lack nuclei
(in cribriform pipes of higher plants and erythrocytes of mammals), but such
cells exist for relatively short time and are not capable to reproduce. They
have possessed nuclei before their differentiation and maturation.
Sharp discussions arise about the presence or absence of nucleus in
bacteria. Some authors accept its existence though it does not combine all
morphological peculiarities characteristic of nuclei in eukaryotic cells, and
others \u2014 reject it categorically. For that reason different names have been
assigned to it \u2014 \u201cgenophore\u201d, \u201cnucleoid\u201d, \u201cchromatin small bodies\u201d, etc.
Usually cells have one nucleus from which, as a result of dividing, their
number increases. Multinuclear cells also exist, where the number of nuclei
reaches to several dozens or hundreds (in osteoclasts of bone tissue, the
symplasts in crossfurrowed muscle fibres, in tumour (HeLa) cells, etc.). The
reasons for the existence of such type of multinuclear cells are unclear.
Sometimes the presence of two nuclei in one cell is conditioned by a
certain differentiation of their functions. Such cases are observed in
Protozoa (Paramecium<\/em>) where the one of the nuclei serves as a source of
genetic information, and the other one controls the metabolic processes of
the cell. This phenomenon characteristic of infusoria is known as nuclear
dualism. In their cells there are two types of nuclei: mitotically dividing,
transcriptionally weakly active diploid micronuclei (generative nuclei) and
such ones dividing by a mode resembling amitosis, rich in DNA,
transcriptionally highly active macronuclei (somatic nuclei). In the course of
the sexual process (conjugation or autogamy) the old macronucleus
degenerates and is replaced by a new, which develops from the
micronucleus (see Raikov, 1989).
It is clear from the above-mentioned that the well-formed nucleus or
nuclear equivalent (nucleoid) is an obligatory and irreversible composite
organelle of every living cell. This shows the enormous role performed by
the nucleus in the life activity and reproduction of the cell. According to
Kudo (1946) nuclear fragments of Protozoa<\/em> with dimensions no more than
1\/50 of the initial cell are capable to regenerate completely the lacking
mass of protoplasm. In this respect worthy of note are the experiments of
H\u00e4mmerling (1953, 1963) with the unicellular green alga Acetabularia<\/em>. They<\/p>\n","protected":false},"excerpt":{"rendered":"

described it as areola usually more dark than the cell envelope, withoutgiving any picture. The term nucleus has been introduced by G. Valentin(1836), who for the first time has described the nucleolus located in it. Thepresence of nucleus in each cell has served as a leading idea for thecreating of cell theory by M. Schleiden […]<\/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-782","post","type-post","status-publish","format-standard","hentry","category-book"],"_links":{"self":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/782","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=782"}],"version-history":[{"count":1,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/782\/revisions"}],"predecessor-version":[{"id":792,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=\/wp\/v2\/posts\/782\/revisions\/792"}],"wp:attachment":[{"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=782"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=782"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cellandcelldivision.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=782"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}