Dictionary » N » Nucleus



noun, plural: nuclei

(general) The core or the central part around which other parts are grouped or gathered.

(biology) The large, membrane-bounded organelle that contains the genetic material, in the form of multiple linear DNA molecules organized into structures called chromosomes.


In biology, the major functions of nucleus are to maintain the integrity of DNA and to control cellular activities such as metabolism, growth, and reproduction by regulating gene expression. It has three main components: the nucleolus, the chromatin and the nuclear envelope. The nuclear envelope has nuclear pores to control the movement of molecules between the nucleoplasm and the cytoplasm.

In other fields, such as:

In Physics, a nucleus refers to the positively-charged center of an atom that usually contains the protons and neutrons.

In Chemistry, a nucleus is a fundamental arrangement of atoms that occur in compounds through substitution of atoms without a change in structure.

In Astronomy, a nucleus is the center of the head of a comet or the central or brightest part of a nebula or galaxy.

In Meteorology, a nucleus is a particle on which water vapor molecules accumulate in free air to form water drops or ice crystals.

In Botany, a nucleus is the central kernel of a nut or seed, or the center of a starch granule.

In Anatomy, a nucleus is a group of specialized nerve cells in the brain or spinal cord.

Word origin: L: kernel, syncopated var. of nuculeus, equiv. to nucu(la) little nut (nuc-, s. of nux nut + -ula -ULE) + -leus n. suffix.

Related forms: nuclear (adjective).

See also: cell, organelle.

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Results from our forum

Newbie question about the first life

... and eukaryotic cells is relatively recent and was made possible when the electronic microscope was developed and it was seen that bacteria have no nucleus and that all other kinds of cells do have one. This changed the way in which creatures are classified. The big difference was not really between ...

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by piscilactovegetarian
Fri Feb 28, 2014 12:10 am
Forum: Molecular Biology
Topic: Newbie question about the first life
Replies: 14
Views: 1036

Newbie question about the first life

... The first creatures were bacteria (that's the plural, the singular being "bacterium"). They are prokaryotic cells (they lack a nucleus). This type of simpler cell has no mitochondria (plural [singular: "mitochondrion"]). Then came the eucharyotic cells (nucleus-bearing ...

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by piscilactovegetarian
Tue Feb 25, 2014 10:21 am
Forum: Molecular Biology
Topic: Newbie question about the first life
Replies: 14
Views: 1036

Totipotent Stem Cell From Molecular Components

... cell from DNA, RNA, Protein, and Fatty Acids as well as Glucose and other sugars. I am wondering. Should I start with the cell membrane or the nucleus and nucleolus(both are very important)? Q2 The pace of DNA replication is 8 2/3 hours for every chromosome and 2097152 of each chromosome in ...

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by caters
Sun Feb 02, 2014 10:58 pm
Forum: Cell Biology
Topic: Totipotent Stem Cell From Molecular Components
Replies: 0
Views: 656

Living or not? (viruses,viroids and prions).

... would distinguish the virus from its host's genetic material, a holdover from the RNA world. It could also explain the existence of a distinct nucleus within Eukaryotic cells. A paper is being released today, however, that argues that this scenario has things exactly backwards. Giant viruses, ...

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by Sumanth001
Sun Dec 08, 2013 12:37 pm
Forum: Microbiology
Topic: Living or not? (viruses,viroids and prions).
Replies: 15
Views: 4783

Re: Multicellular prokaryote

... that conceptualization and I hope I can answer it, though no one really knows any of these answers: The very defining feature of a eukaryote was a nucleus, and there is reason to believe that these other important characteristics are related to that and to each other: endomembrane system, membrane ...

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by thirdprometheus
Fri Nov 15, 2013 7:45 pm
Forum: Microbiology
Topic: Multicellular prokaryote
Replies: 24
Views: 17842
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