Nucleus: Meaning and Definition of a Nucleus, Structure of Nucleus

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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

3D Rendering of Nucleus

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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.