Nucleus STRUCTURE and FUNCTION

The most integral component of the cell is the nucleus (plural: nuclei). It is derived from a Latin word which means “kernel of a nut”.

Nucleus Definition

A nucleus is defined as a double-membraned eukaryotic cell organelle that contains the genetic material.

Diagram human cell nucleus

Structure Of Nucleus

  • Typically, it is the most evident organelle in the cell.
  • The nucleus is completely bound by membranes.
  • It is engirdled by a structure referred to as the nuclear envelope.
  • The membrane distinguishes the cytoplasm from the contents of the nucleus
  • The cell’s chromosomes are also confined within it.
  • DNA is present in the Chromosomes, and they provide the genetic information required for the creation of different cell components in addition to the reproduction of life.

Nucleus Function

Following are the important nucleus function:

  • It contains the cell’s hereditary information and controls the cell’s growth and reproduction.
  • The nucleus has been clearly explained as a membrane-bound structure that comprises the genetic material of a cell.
  • It is not just a storage compartment for DNA, but also happens to be the home of some important cellular processes.
  • First and foremost, it is possible to duplicate one’s DNA in the nucleus. This process has been named DNA Replication and produces an identical copy of the DNA.
  • Producing two identical copies of the body or host is the first step in cell division, where every new cell will get its own set of instructions.
  • Secondly, the nucleus is the site of transcription. Transcription creates different types of RNA from DNA. Transcription would be a lot like creating copies of individual pages of the human body’s instructions which may be moved out and read by the rest of the cell.
  • The central rule of biology states that DNA is copied into RNA, and then proteins.

Structure of the Nucleolus

In eukaryotic cells, nucleolus has a well-ordered structure with four main ultrastructural components. The components can be further identified as:

NucleolusNCc
  • Fibrillar Centers: It is the place where the ribosomal proteins are formed.
  • Granular Components: Before ribosomes are formed, these components have rRNA that binds to ribosomal proteins.
  • Dense Fibrillar Components: It has new transcribed RNA, which connects to the ribosomal proteins.
  • Nucleolar vacuoles: It is present only in plant cells.

The ultrastructure of the nucleolus can be easily visualized through an electron microscope.  The arrangement of the nucleolus within the cell can be clearly studied by the techniques –  fluorescent recovery after photobleaching and fluorescent protein tagging.

The nucleolus of several plant species has very high concentrations of iron in contrast to the human and animal cell nucleolus.

Nucleolus Function

The nucleolus is considered as the brain of the nucleus, covering nearly 25% volume of the nucleus. Primarily, it takes part in the production of subunits that unites to form ribosomes. Hence, nucleolus plays an important role in the synthesis of proteins and in the production of ribosomes in eukaryotic cells.

The difference between nucleus and nucleolus is mentioned below:

NucleusNucleolus
Large in sizeVery small in size
Bound by the nuclear envelopeIt has no limiting membrane
It contains chromosomes.It does not hold any chromosomes
It is rich in DNA, the genetic materialIt is rich in RNA

What is the Nuclear Membrane?

All the eukaryotic cells that are found in plants, animals, fungi, and protists have a control centre, called a nucleus where DNA is stored. Every nucleus is girdled and covered by a double-layered membrane, known as the nuclear envelope or nuclear membrane. It separates the nucleoplasm (the fluid present in the nucleus), from the cytoplasm.

He nuclear membrane is present in both the plant and animal cells. Cells carry out a multitude of functions such as protein building, conversion of molecules into energy and elimination of unnecessary products.

This membrane guards the genetic material of the cells against the exterior of the nucleus where chemical reactions are taking place. Also, it carries several proteins which are crucial in the organization of DNA  and to control genes.

Nuclear Membrane Structure

A nuclear membrane is composed up of two membranes – an inner and an outer membrane. Both membranes consist of phospholipids that are organized in a bilayer. The complete nuclear membrane includes four series of phospholipids.

The perinuclear space separates the outer and inner membrane. The outer membrane works by the rough endoplasmic reticulum. It is an organelle which is important in the transportation of proteins.

Nuclear Membrane Structure

The outer membrane and the rough endoplasmic reticulum both are covered in ribosomes as these are the true location of protein production.

Endomembrane system diagram en

On the nucleoplasm, nuclear lamina is connected to the inner nuclear membrane. The nuclear lamina also attaches to and secures chromatin which is organized loosely in protein structure and DNA. A protein layer gives support and strength to the nuclear membrane.

Parts Of Nuclear Membrane

Parts Of Nuclear Membrane

The nuclear membrane encloses the cell nucleus and consists of the following parts:

Outer Membrane

It is a lipid bilayer containing two layers of molecules of lipid. The outer layer is made up of lipids which have ribosomes on the surface that are linked to the endoplasmic reticulum.

Inner Membrane

It contains proteins that rearrange the nucleus and chain the genetic material in position. The nuclear lamina is the attachment of proteins and fibres that are linked to the inner membrane. It provides structural support to the nucleus, assists in DNA repair, controls cell cycle events such as cell division and also on DNA replication.

Nuclear Pores

They move through both the inner and outer membranes of the nuclear membrane and are composed of large complex proteins which allow a few molecules to permeate by the nuclear envelope. Each of the nuclear pores consists of 30 distinct proteins which operate together to transfer materials. Also, they link the inner and outer membranes.

NuclearPore crop

A cross section of a nuclear pore on the surface of the nuclear envelope 

(1). Other diagram labels show

(2) the outer ring,

(3) spokes,

(4) basket, and

(5) filaments.

Nucleolus

These are tiny spherical bodies that are situated in the nucleus as they are usually present in a centralized site but are typically found closer to the nuclear membrane. What sets them apart from other nuclear material is that they are built by the (NOR) nucleolus organizing region of chromosomes, which is known to store the genes that are necessary for full ribosomal production. They encode ribosomal RNA subunits. 

Nucleoplasm

Nucleoplasm is a remarkably viscous liquid that contains the nuclear hyaloplasm which is the more soluble and liquid portion of the nucleoplasm. It is a type of protoplasm that is similar to the cytoplasm, which is present throughout the cell body to the exterior of the nucleus.

As specific functions are carried out inside the nucleus, a different type of protoplasm is required. The constituents of the nucleoplasm are water, dissolved ions, and a blend of other substances. This element is completely confined in the nuclear envelope containing nucleotides and crucial enzymes that promote replication.

Nuclear Membrane Function

Following are the important functions of the nuclear membrane:

  • The nuclear envelope has tiny holes which are identified as nuclear pores. The pores enable the content to flow in and out of the nucleus. It also connects the outer membrane and the inner membrane.
  • The nuclear envelope’s surface area extends and doubles the nuclear pores during the interphase part of cell division.
  • Nuclear membrane shields the nucleus with a double membrane by many pores that help in controlling the crossing of macromolecules such as proteins and RNA and permit free passage of water, ions, ATP and small molecules. The membrane controls the flow of information in the cell as it is conducted by the macromolecules.

Function Of Nucleus

The nucleus is a double-membrane bound cell organelle that is located in the eukaryotic cells and composes of the cell’s genetic material – the DNA. Since it maintains the integrity of the genes that control the gene expression hence controlling the cell’s activities, it is known as the control centre of the cell.  

The following are the different roles of the nucleus:

  • It is responsible for regulating the heredity traits of an entity
  • It controls protein synthesis, growth, cell division, and differentiation
  • It reserves heredity material in the form of DNA strands that also store RNA and proteins in the nucleolus
  • It is a section for the process of transcription wherein mRNA is produced to generate proteins
  • Assists in the exchange of RNA and DNA between the cell and the nucleus
  • The nucleolus generates ribosomes that are referred to as protein factories
  • It controls the integrity of gene expression and genes

Difference between Cytoplasm and Nucleoplasm

The important difference between cytoplasm and nucleoplasm are as follows:

CytoplasmNucleoplasm
Found inside the cell, outside the nucleus.Found inside the nucleus.
Enclosed by the cell membrane.Enclosed by the nuclear envelope.
Gelatinous structure.Highly gelatinous structure.
Found in all the known cells.Found only in eukaryotic cells.
Inclusions and organelles are suspended in the cytoplasm.Nucleoplasm is composed of nucleolus and chromatin.
It divides during cytokinesis.It is released during nuclear division and is refilled after the nuclear envelope forms.

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