Nucleus: Meaning and Definition of a Nucleus, Structure of Nucleus (For CBSE, ICSE, IAS, NET, NRA 2022)

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Meaning and Definition of Nucleus

  • Nucleus can be defined as a double-membraned eukaryotic cell organelle that contains the genetic material.
  • It is the most important component of the cell.
  • The word nucleus has been derived from the Latin word which means “kernel of a nut.”
3D Rendering of Nucleus

Structure of Nucleus

  • It is completely bounded by the membranes.
  • A nuclear envelope engirdles it.
  • DNA provides the genetic information required for the creation of different cell components.
  • The chromosomes of the cells are confined within it.
  • The structure of a nucleus encompasses:
    • The nuclear membrane
    • Nucleoplasm
    • Chromosomes
    • Nucleolus

Nuclear Membrane

  • A double-layered structure encloses the contents of the nucleus.
  • The nuclear envelope helps to maintain the shape of the nucleus.
    • Also assists in regulating the flow of molecules.
  • The nuclear pores act as the sites for the exchange of large molecules (proteins and RNA) .
  • Between the two layers of a nuclear membrane, a fluid-filled space or perinuclear space is present.


  • It is the gelatinous substance present in the nuclear envelope.
  • The nucleoplasm surrounds the nucleolus and chromosomes.
    • Functions to cushion and protect the contents of the nucleus.
  • It also supports the nucleus by helping to maintain its shape.


  • It is a dense, membrane-less structure composed of RNA.
  • The proteins are called the nucleolus.
  • The nucleolus contains nucleolar organizers.
  • The nucleolus disappears when a cell undergoes division.


  • The nucleus houses chromosomes.
  • Chromosomes consist of DNA.
  • Contains heredity information.
  • Instructions for cell growth, development, and reproduction.

Functions of Nucleus

  • It controls and regulates the activities of the cell.
  • The hereditary information is contained within.
  • The cell՚s growth and reproduction are controlled by the nucleus.
  • DNA Replication:
    • Duplicate one՚s DNA in the nucleus.
    • An identical copy of the DNA is produced.
  • It provides a site for genetic transcription.
    • Segregated from the location of translation in the cytoplasm.
  • It acts as the storage of hereditary material.
  • Its further acts as a storage of proteins and RNA (ribonucleic acid) in the nucleolus.
  • Chromatins are arranged into chromosomes in the nucleus during the process of cell division.

Significance of the Nucleus

  • It regulates and coordinates different life processes of the cell.
  • It consists of genes, which determine heredity.
  • It plays an important role during the cell division process.


  • It means nucleus-like.
  • It is an irregularly shaped region within the cell of a prokaryote.
  • It contains all or most of the genetic material.
  • It is not surrounded by a nuclear membrane.
  • It is essential for controlling the activity of the cell and reproduction.
    • Transcription and replication of DNA take place.


Q 1. What is a Nucleus?


A nucleus is a double-membraned organelle that contains the genetic material and other instructions required for cellular processes.

Q 2. What are the two important functions of a nucleus?


The two important functions of a nucleus are:

i) It stores the cell՚s hereditary material or the DNA.

ii) Its further acts as a storage of proteins and RNA (ribonucleic acid) in the nucleolus.

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