Nucleus Structure and Function in Animal Cell

In this nucleus structure and function in animal cell post we have briefly explained about nucleus in animal cell, definition, origin, structure, and functions.

Nucleus Structure and Function in Animal Cell

Nucleus the most prominent organelle of the cell. The number of nuclei may vary, they may be uninucleate (single nucleus), binucleate (two nuclei) or even multi-nucleate. Certain eukaryotic cells such as the mature sieve tubes of higher plants and mammalian erythrocytes contain no nucleus.

Prokaryotic cells lack nucleus and is complemented by nucleoid. The contents are DNA genome, RNA synthetic apparatus, and a fibrous matrix.  It is surrounded by two membranes, each one a phospholipid bilayer containing many different types of proteins.

The inner nuclear membrane defines the nucleus in animal cell itself. In most cells, the outer nuclear membrane is continuous with the rough endoplasmic reticulum, and the space between the inner and outer nuclear membranes is continuous with the lumen of the rough endoplasmic reticulum.

The two nuclear membranes appear to fuse at nuclear pores, the ring-like complexes composed of specific membrane proteins through which material moves between the nucleus and the cytosol.

It contains cell’s genetic material, organized as multiple long linear DNA molecules in complex with histones, to form chromosomes. The genes within these chromosomes are the cell’s nuclear genome.

Definition

In cell biology, the nucleus in animal cell (plural-nuclei; from Latin nucleus or nuculeus, meaning kernel or seed) is a membrane-enclosed organelle found in eukaryotic cells.

Eukaryotes usually have a single nucleus in animal cell, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others have many.

Human skeletal muscle cells have more than one nucleus, as do eukaryotes like fungi. Cell nuclei contain most of the cell’s genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes.

The genes within these chromosomes are the cell’s nuclear genome and are structured in such a way to promote cell function.

The nucleus in animal cell maintains the integrity of genes and controls the activities of the cell by regulating gene expression it is, therefore, the control center of the cell.

Origin

A study of the comparative genomics, evolution and origins of the nuclear membrane led to the proposal that the nucleus in animal cell emerged in the primitive eukaryotic ancestor, and was triggered by the archaeo-bacterial symbiosis. Several ideas have been proposed for the evolutionary origin of the nuclear membrane.

These ideas include the invagination of the plasma membrane in a prokaryote ancestor, or the formation of a genuine new membrane system following the establishment of proto-mitochondria in the archaeal-host.

The adaptive function of the nuclear membrane may have been to serve as a barrier to protect the genome from reactive oxygen species (ROS) produced by the cells’ pre-mitochondria.

Structure

Nucleus

Nucleus Structure and Function in Animal Cell

The structure of encompasses the nuclear membrane, nucleoplasm, chromosomes, and nucleolus.

Nuclear Membrane

The nuclear membrane is a two-layered structure that surrounds the nucleus’ content. The endoplasmic reticulum is attached to the membrane’s outer layer. The nuclear envelope, like the cell membrane, is made up of phospholipids that form a lipid bilayer.

Shape is maintained by the envelope, which also helps to regulate the movement of chemicals into and out of the nucleus in animal cell through nuclear pores. The nucleus in animal cell communicates with the rest of the cell or the cytoplasm via nuclear pores, which are small holes in the nucleus.

Large molecules (proteins and RNA) are exchanged between the nucleus in animal cell and the cytoplasm through nuclear pores. A fluid-filled space or perinuclear space is present between the two layers of a nuclear membrane.

Nucleoplasm

The gelatinous substance within the nuclear membrane is called nucleoplasm. This semi-aqueous material, also known as karyoplasm, is similar to cytoplasm and is primarily made up of water with dissolved salts, enzymes, and organic molecules suspended inside.

Nucleoplasm surrounds the nucleolus and chromosomes and serves to cushion and protect the contents of the nucleus in animal cell.

It is additionally supported by nucleoplasm, which helps in the preservation of its form. Furthermore, nucleoplasm serves as a transport medium for molecules such as enzymes and nucleotides (DNA and RNA subunits) within the nucleus in animal cell. Nuclear pores allow substances to move between the cytoplasm and nucleoplasm.

Nucleolus

It is a compact, membrane-less structure made up of RNA and proteins that resides within the nucleus in animal cell. Some eukaryotic species can have up to four nucleoli.

Nucleolar organisers, which are portions of chromosomes having ribosome synthesis genes on them, are found in the nucleolus. By transcribing and assembling ribosomal RNA subunits, the nucleolus aids in the formation of ribosomes. During protein synthesis, these components come together to create a ribosome.

When a cell divides, the nucleolus vanishes and reappears once the division process is completed.

Chromosomes

It is the organelle that houses chromosomes. Chromosomes consist of DNA, which contains heredity information and instructions for cell growth, development, and reproduction.

Chromosomes are present in the form of strings of DNA and histones (protein molecules) called chromatin. When a cell is “resting” i.e. not dividing, the chromosomes are organized into long entangled structures called chromatin.

The chromatin is further classified into heterochromatin and euchromatin based on the functions. The former type is a highly condensed, transcriptionally inactive form, mostly present adjacent to the nuclear membrane. On the other hand, euchromatin is a delicate, less condensed organization of chromatin, which is found abundantly in a transcribing cell.

Nucleus contains a number of other non-membrane-delineated bodies. These include Cajal bodies, Gemini of coiled bodies, polymorphic interphase karyosome association (PIKA), promyelocytic leukemia (PML) bodies, paraspeckles, and splicing speckles.

Functions

1. Storage of hereditary material, the genes in the form of long and thin DNA (deoxyribonucleic acid) strands, referred to as chromatins.

2. Storage of proteins and RNA (ribonucleic acid) in the nucleolus. It is responsible for protein synthesis, cell division, growth and differentiation.

3. Nucleus in animal cell is a site for transcription in which messenger RNA (mRNA) are produced for the protein synthesis.

4. It controls the heredity characteristics of an organism. Exchange of hereditary molecules (DNA and RNA) between the nucleus in animal cell and rest of the cell.

5. During the cell division, chromatins are arranged into chromosomes in the nucleus. Production of ribosomes (protein factories) in the nucleolus.

6. Selective transportation of regulatory factors and energy molecules through nuclear pores. It also regulates the integrity of genes and gene expression.

Nucleus in Animal Cell

Nucleus in animal cell is a membrane bound organelle. It is surrounded by double membrane. The nucleus in animal cell communicates with the surrounding cell cytoplasm through the nuclear pores.

The DNA in the nucleus in animal cell is responsible for the hereditary characteristics and protein synthesis. The active genes on the DNA are similar, but some genes may be turned on or off depending on the specific cell type.

This is the reason why a muscle cell is different from a liver cell. Nucleolus is a prominent structure in the nucleus. This aids in ribosomes production and protein synthesis.

Plant Cell Nucleus

Plant cell nucleus is a double-membrane bound organelle. It controls the activities of the cell and is known as the master mind or the control center of the cell.

The plant cell wall has two layers the outer membrane and the inner membrane, which encloses a tiny space known as perinuclear space.

It communicates to the cell cytoplasm through the nuclear pores present in the nuclear membrane. The nuclear membrane is continuous with the endoplasmic reticulum. The DNA is responsible for cell division, growth and protein synthesis.

Bacterial Cell Nucleus

Bacteria are minute single-celled microorganisms under the domain Prokaryota. Interestingly, they are believed to be the direct descendants of the first ever organisms that thrive on Earth about 3.5 billion years ago.

While they seem to be invisible with the naked eye, under powerful microscopes, the structures within bacteria can be observed. The bacterial cell does not contain any nucleus.

The bacterial chromosome is not enclosed in a membrane bound nucleus. The bacterial chromosome is circular and located in the cytoplasm.

Further Readings

Reference