Nucleus | definition, functions, structure, composition | Edumistic

 Nucleus - definition, functions, structure, composition

Nucleus

Definition

Nucleus is the largest and Central part of the cell that contain many components. Nucleus is involved in the facilitating transcription and replication and reproduction processes.

Nucleus have a four main components

1. phospholipids

2. chromatin

3. nucleoplasm

4. nucleolus

Nucleus is present in many Eukaryotic cells such as animals cells. Some Eukaryotic animals have more than one nucleus likes slime molds. Some lacks nucleus called enucleate like as erythrocytes (RBCs).

Chemical composition of nucleus:

Components	Percentage
DNA	9-12%
Histone proteins	15%
Enzymes ( neutral and acidic proteins)	65%
RNA	5%
lipids	3%

Structure of nucleus:

Nucleus play important role to maintain the structure of cell. It have many components which perform their specific function in the cell that is why it is typically called as command center of the cell.

It is vary in size and shape depend on the types of cell mostly it looks like flattened, ellipsoidal and irregular.

Now we discuss the components of nucleus one by one in detailed.

Nuclear Membrane:

Nuclear membrane is the main difference between prokaryotic and Eukaryotic cells.

Nuclear membrane is a double layered structure have many components such as

• Phospholipids (lipid bilayer)

• nuclear pores  ( made up of proteins, RNA)

• perinuclear cisterna  (space between bilayer of phospholipids)

Nuclear membrane is also attached with endoplasmic reticulum and play important role in the transportation of things in the nucleus and out of the nucleus through the nuclear pores.

It also provide the site of attachment for the pore complexes.

Helpful in regulating gene expression.

1  Nucleoplasm:

       It includes the chromosomes and nucleolus. Also named as karyoplasm and nucleus SAP and karyolymph. Helps to maintain shape of nucleus. It is a variety of protoplasm made up of enzymes, dissolved Salts, and organic components.

 Nucleolus:

Spherical shaped organelle. Have no membrane around itself. Ribosomes biogenesis also occur in the nucleolus.

Nucleolus vary in size with protein synthesis. For example; during protein synthesis nucleolus is larger than the normal size. Some organisms nucleus consists of four nucleoli.

Chromosomes:

Thread like structure containing genetic information involved in cell division and replication processes such as translation and transcription.

Chromosomes are bind with each other and form a double helix structure called DNA. About three billions chromosomes are tightly packed in the nucleus.

DNA strand is tightly packed in the bead like structure called histone protein. histone proteins are alkaline in nature.

Structure of chromosome:

A chromosome structure contain following important things.

• Kinetochores

Complex of proteins lies in the centromere helpful in the attachment of spindles during cell division.

• Telomeres

End point of the chromosome is called telomere.

• Chromatids

When a pair of chromosomes are separated with each other and form a two a two longitudinal threadlike strands which is called chromatids.

 

Main functions of nucleus:

• Involved in cellular metabolism.

• It contain hereditary material

• DNA strands , RNA, and proteins are synthesized and stored in it

• Messenger RNA are synthesized in the nucleus which involved in transcription process.

• Many binding proteins are synthesized in it.