Nucleus: Structure and Function

The nucleus (plural: nuclei) is a double-membraned organelle that is found only in eukaryotic cells. The name nucleus comes from a Latin term that means “nut kernel.” The nucleus was discovered by Robert Brown in 1831. It is the first cell organelle that was discovered.

The nucleus is responsible for containing the genetic material that holds the key to regulating all sorts of cellular activities. The presence and absence of the nucleus is one of the important characteristics that differentiate between the two main types of cells.

What is a Nucleus?

The nucleus is the unique characteristic of eukaryotic cells and is only present in eukaryotes. Prokaryotic cells don’t have a true nucleus, instead, they have nucleoids.

The nucleus is a double membrane-bound organelle that contains the cell’s genetic material in the form of DNA, which is organized into structures called chromosomes. The nucleus is usually the largest organelle in the cell and is covered by a double membrane called the nuclear envelope, on which nuclear pores are present that allow the movement of certain molecules in and out of the nucleus.

Inside the nucleus, the DNA is organized into long strands of chromatin, which can condense into discrete chromosomes during cell division. The nucleus also contains a nucleolus, which is a structure that produces ribosomes, the cellular machines that synthesize proteins.

Also Read: Difference between Prokaryotic and Eukaryotic Cell

Characteristics of Nucleus

Following are some of the general characteristics of a cell’s nucleus;

• It is typically the cell organelle present in almost every cell.
• The nucleus is covered by a double layer of membrane called the nuclear envelope.
• The cytoplasm and the nucleus’s contents are separated by the nuclear membrane.
• The chromosomes of the cell are present within the nucleus.
• The chromosomes, which contain DNA, supply the genetic information that is necessary for the synthesis of various cell components as well as for the generation of life.
• The presence of nuclear pores on the envelope of the nucleus facilitates the movement of substances between the nucleus and the cytoplasm.

Structure of Nucleus

The nucleus is divided into different subparts, those are:

Nuclear Membrane

The nuclear envelope is the other name of the nuclear membrane. It is a double membrane structure that differentiates the cytoplasm and nucleoplasm of the eukaryotic cell. The nuclear membrane is composed of 2 lipid layers, one is outer and the other one is inner. The space present between the 2 layers is known as periplasmic space. Porous structures are present over the nuclear membrane which helps in the transportation of transcriptional factors, proteins, and RNAs.

Chromosome

A chromosome is a structure that is composed of DNA and proteins present in the nucleus. These are the thread-like structures that are seen under the microscope at the time of cell division. The DNA is highly coiled over the histone protein that forms the chromatin. Chromatin can further divide into heterochromatin (highly condensed DNA) and euchromatin (loosely packed DNA). Chromosomes are numbered according to their size, with the largest being chromosome 1 and the smallest being the sex chromosomes, X and Y.

Nucleic Acid

Nucleic acids are large biomolecules, or macromolecules, present in all living cells. They are responsible for carrying and transmitting genetic information from one generation to the next and are essential for the function and survival of cells and organisms. Two types of nucleic acid are found that are DNA and RNA. The DNA is made up of four building blocks called nucleotides – adenine (A), cytosine (C), guanine (G), and thymine (T) – they linked together in a specific sequence to form a long, double-stranded helix. Whereas, in the case of RNA Uracil (U) is present in place of Thymine (T) and the rest are the same.

Nuclear Sap

It is a clear, transparent, homogenous colloidal liquid enclosed in the nuclear membrane. The nucleoplasm is a complex solution containing ions, enzymes, nucleotides, and various other biomolecules necessary for the cell’s genetic activity. The nucleoplasm contains genetic material in the form of chromatin, which is the complex of DNA, histone proteins, and other associated proteins. Within the nucleoplasm, there is also the nucleolus, which is a dense region that produces ribosomes, the cellular machines that synthesize proteins.

Nucleolus

The unique structure inside the nucleus of eukaryotic cells is called the nucleolus. It mainly takes part in ribosome assembly, synthesizes and stores RNA, and detects oxidative stress. RNA and proteins, which develop around particular chromosomal areas, make up the nucleolus. It is a significant part of the nucleus. The nucleolus is mainly composed of DNA, RNA, proteins, as well as other elements.

Diagram of Nucleus

The labeled diagram of nucleus is shown below:

Diagram of Nucleus

Function of Nucleus

The nucleus is responsible for containing the genetic material that regulates the hereditary characteristics of the cell. Other than that there are some important functions that the nucleus performs;

• The nucleus regulates the cell’s growth and reproduction as it contains the cell’s genetic information.
• Proteins would move across the nucleus with the help of a signal called a nuclear export signal.
• The genetic makeup of a cell is contained in the nucleus.
• In addition to serving as a DNA storage space, it also serves as the location of various significant cellular functions.
• In the nucleus, one’s DNA can be duplicated first and foremost by the process of DNA replication.
• Cell division begins with creating two exact replicas of the parent DNA, with each new cell receiving a unique set of DNA and nucleus.
• Secondly, transcription takes place in the nucleus. Different RNA types are produced by transcription from DNA.
• When cell division occurs the chromatin fibers are arranged into chromosomes inside the nucleus that can be observed.
• The synthesis of ribosomes also occurs inside the nucleus.

Types of Cells Based on the Nucleus

There are four main categories of cells based on presence-absence and number of nuclei, these are;

1. Enucleate Cell: Some cells like human RBCs, plant sieve cells, etc. lack a nucleus and are called enucleated cells.
2. Uninucleate Cell: Most of the plant and animal cells have only one nucleus.
3. Binucleate Cell: Some cells like liver cells, Paramecium, etc. during fusion or division pass through a phase called the dikaryotic phase in which they possess two nuclei.
4. Multinucleate Cell: Some cells like slime molds, striated muscle cells, etc. contain more than two nuclei at a time and are called polynucleated cells.

FAQs on Nucleus

1. What is the nucleus?

Answer:

All genetic information and other instructions necessary for the cellular functions of a cell are present in the double membrane organelle known as the nucleus. It is one of the biggest organelles and is only present in eukaryotic cells.

2. Nucleus is discovered by?

Answer:

Robert Brown discovered the nucleus in 1831.

3. Describe some functions of the nucleus.

Answer:

The nucleus serves two main purposes:

• It is in charge of keeping the DNA or other genetic material within the cell.
• It is in charge of organizing a variety of crucial cellular processes, including the synthesis of proteins, cell division, growth, and a number of other crucial operations.

4. What are the main parts of the nucleus?

Answer:

The main parts of the nucleus are; the nuclear membrane, genetic material, nucleolus, and nucleoplasm.

5. Define the structure of the nucleus.

Answer:

The general structure of a nucleus is spherical-shaped with double membrane having nuclear pores in the membrane.