Difference Between Nucleus and Nucleolus: Nucleus and Nucleolus are present inside eukaryotic cells. The main difference between nucleus and nucleolus is that nucleus is an organelle present in the cell and is bounded by a nuclear envelope whereas nucleolus is a sub-organelle present inside the nucleus and is not bounded by any membrane.
Table of Content
Difference Between Nucleus and Nucleolus
| Features | Nucleus | Nucleolus |
|---|---|---|
| Location | Organelle present in the cell, bounded by the nuclear envelope | Sub-organelle present inside the nucleus, not bounded by a membrane |
| Composition | Contains genetic material (DNA) | contains RNA |
| Structure | Bounded by the nuclear envelope, with inner and outer membranes | Not bounded by any membrane |
| Size | Largest organelle in eukaryotic cells | Largest sub-organelle in the nucleus |
| Presence | Present in all eukaryotic cells except RBCs and Sieve Tube | Found only in higher eukaryotes |
| Volume | Occupies a significant portion of the cell | Occupies 25 per cent of the volume of the nucleus |
| Function | The control centre of the cell stores genetic material (DNA), Controls DNA replication during the cell cycle | Involved in ribosome biogenesis, nuclear detention, and assembling the signal recognition particles. |
| Transcription | Site of DNA transcription into hnRNA and mRNA | Involved in transcription of DNA into rRNA |
What is Nucleus?
The nucleus is the largest organelle present only in eukaryotic cells. It was discovered in 1831 by Robert Brown in Orchid. It is a membrane-bound organelle present in all eukaryotic cells except RBCs and Sieve Tube. It is located at the centre of all animal cells except adipocytes. It is peripheral in plant cells. Generally, one cell contains one nucleus. There are some cells that are syncytium (Multinucleated) like the Endosperm of coconut, Plasmodium, Skeletal muscle etc. to increase metabolic activity.
Structure of Nucleus
To study Nucleus, it is observed in the interphase of the cell cycle. It is visible as a dense structure under a light microscope after staining. The detailed structure can be viewed under the electron microscope.
- Nuclear membrane- The nucleus is bounded by two membranes known as Nuclear Envelope. The outer membrane is in continuation with the Endoplasmic Reticulum. The inner membrane is in contact with Nucleoplasm.
- Perinuclear space- It is 10-50nm space between two membranes. It can be observed only under the electron microscope.
- Nuclear pore- When outer and inner membranes come in contact with each other, a Nuclear pore is generated. A protein is present in the pore that helps in transport. The pore and protein are collectively known as Nuclear Pore Complex. It helps in the transport of some proteins like Histones and enzymes like DNA Polymerase, and RNA Polymerase from the cytoplasm to the nucleus. And RNA, subunits of ribosomes from the nucleus to the cytoplasm.
- Nucleoplasm- It is also known as Nuclear Matrix. It contains Nucleolus and Chromatin.
Functions of Nucleus
The nucleus is known as the "Control centre" of the cell. It controls cell division and cell growth. It stores genetic material i.e.DNA.
Transcription of DNA into hnRNA, splicing (removing introns) of hnRNA to form mRNA, and Post-transcriptional modifications occur in the nucleus. Thus, Nucleus plays an important role in controlling gene expression, heredity and inheritance.DNA replication is also controlled by the nucleus during the cell cycle.
What is Nucleolus?
Nucleolus is the largest sub-organelle present inside the nucleus. It was discovered by Felice Fontana in 1774. It occupies 25 per cent of the volume of the nucleus. It is not bounded by any membrane. It is found only in higher eukaryotes. The number of nucleolus is variable. Cells that require more protein have more nucleolus in their nucleus.
Structure of Nucleolus
Nucleolus can be observed under the electron microscope. The nucleolus is made up of DNA, RNA and proteins.
The nucleolus is made up of:
- Dense Fibrillar Component (DFC)
- Fibrillar centre (FC)
- Granular component (GC)
Functions of Nucleolus
The nucleolus is involved in the transcription of DNA into rRNA. rRNA further forms ribosomes. Thus, Nucleolus helps in ribosome biogenesis.
There are three types of RNA Polymerases for different types of rRNA.
- RNA Polymerase I forms 28S, 18S, and 5.8S rRNA
- RNA Polymerase II forms ribosomal protein
- RNA Polymerase III forms 5S rRNA.
Ribosomal proteins and rRNA get assembled to form subunits of ribosomes.
Nucleolus helps in nuclear detention which means capturing and immobilising proteins. It also helps in assembling the signal recognition particles.