Nucleoplasm
Nucleoplasm Definition: The semi-liquid, slightly acidic, non-pigmented, almost transparent, granular fluid present in the space between the nuclear membrane and nucleolus, is called nucleoplasm.
Nucleoplasm Ultrastructure: It contains nucleic acid, protein, different types of enzymes (DNA polymerase, RNA polymerase, nucleotide transferase, nucleoside phosphorylase, kinase, dehydrogenase, endonuclease, etc.), cofactors (CoA, ATP), minerals (calcium, magnesium, phosphorus), RNP granules (ribonucleoprotein particles) and fewer lipids.
Nucleoplasm Functions:
- It helps in the synthesis of DNA, and RNA. It also acts as a storehouse of the components required for protein synthesis.
- It maintains the turgidity of the nucleus.
- It houses nucleolus and chromatin.
Definition: Thread-like coiled, elongated structure, present in the nucleoplasm and stained with basic stain and which condenses during cell division, to form chromosomes is called chromatin.
During interphase stage i.e., during the non-dividing stage, chromatin appears like thread and forms a reticular structure. These are known as chromatin fibers.
During cell division, the chromatin condenses into thick, compact, and dense structures. This structure is known as a chromosome.
” components of nucleus “
Ultrastructure: Chromatin is mainly composed of a combination of DNA, proteins (histones and non-histones), and some RNA (DNA-31%, RNA-5%, histone- 36%, non-histone protein-28%).
The histones form disc-like structures around which portions of the DNA wrap themselves to form structural units, called nucleosomes. This structure resembles beads along a string.
The chromatin fibers are distributed in the nucleoplasm.
Chromatin exists in two conformational states—
Heterochromatin The condensed and more coiled, deeply stained, non-functional, inert regions of the chromosome are known as heterochromatin. These regions possess highly repetitive base sequences of DNA that are genetically inactive (i.e., do not take part in gene expression).
Heterochromatin is late replicating in nature i.e., replicates in late S-phase.
Heterochromatin is of two types—
- Facultative and
- Constitutive heterochromatin.
“define nucleoplasm “
Facultative heterochromatin: The chromatin, that remains condensed and non-functional (heterochromatin-like) in certain cell types or in special stages of development, is known as facultative heterochromatin.
It remains euchromatin-like in other stages. For, one of the X chromosomes in somatic cells of mammalian females gets heterochromatinised to form a ‘Barr body’ (inactive X-chromosome) during interphase.
Constitutive heterochromatin: The chromatin, that remains permanently condensed and nonfunctional throughout the cell cycle, is known as constitutive heterochromatin.
Constitutive heterochromatin is found in the centromeric region of the chromosome and the greater part of the human Y chromosome.
“nucleoplasm definition “
Euchromatin: The less coiled, lightly stained functional part of the chromatin is known as euchromatin.
These regions possess less repetitive base sequences of DNA which is genetically active (i.e., it takes part in gene expression through mRNA and during protein synthesis) during interphase. It replicates during the early ‘S’ phase.
“nucleoplasm function “
Functions: Chromatin constitutes genes. It carries and transfers genes in living organisms. The euchromatin associated with acidic proteins, is involved in the transcription process to synthesise RNA from DNA.
Nucleolus
Nucleolus Definition: The deeply stained, spherical, non-membranous structure that is composed of protein and nucleic acids, is found within the nucleus and which plays an important role in ribosome synthesis is called the nucleolus.
Origin and location: It originates from one or two nuclear chromatins. It emerges from the nuclear or SAT chromosome (a part of the chromosome that is separated from the main chromosome body by a secondary constriction) during the telophase stage (phase of cell division) and attaches to the nuclear organizer region (secondary constriction).
It does not form from each chromosome. The Nucleolar Organiser region (NOR) is composed of tandem repeats (repetition of one or more adjacent nucleotides) of rRNA genes, which can be found in several different chromosomes.
Discovery: The nucleolus was discovered by Fontana and its detailed structure was studied by Wagner (1832). The term ‘nucleolus’ was coined by Bowman.
Number a ltd shape: Generally, a nucleus may contain 1-4 nucleoli. The shape and number depend on the metabolic activity of the cell.
In highly active cells (neurons, oocytes, secretory cells kidney cells, etc.) where proteins, enzymes, and other substances are synthesized more, their size enlarges and they also increase in number.
Again, in less active cells, the nucleolus is either absent or smaller in size.
Ultrastructure: Nucleolus is not surrounded by a membrane. It is believed that calcium ion maintains its structural integrity.
Its four main components are—
- Chromatin part,
- Pars amorpha or amorphous matrix,
The dense fibrillar component (dfc) or pars fibrillosa and 0 granular components (gc) or pars granulosa.
Chromatin part: The chromatin thread formed from DNA at the exterior of the nucleolus, is known as perinucleolar chromatin.
A part of this chromatin takes a tubular shape and extends to the matrix. This is known as intranuclear chromatin. It helps in rRNA formation.
Pars amorpha: Proteinaceous matrix that contains floating granular and thread-like parts.
Pars fibrillose: It is a centrally located thin thread (50-80A) of ribonucleoprotein. It is also known as nucleolonema.
Pars granulosa: They are the ribonucleoprotein granules (150-200A diameter) in the matrix. Ribosomes are synthesized from here.
Functions:
- The nucleolus is known as the ribosome factory as it is involved in the synthesis of ribosomes.
- It stores ribosomal protein.
- It participates in the formation of spindle fibers.
Functions of nucleus
Controls cellular metabolism: Nucleus controls all the metabolic activity of cells and so, is known as the brain of the cell.
Carrier of genetic material: Chromatin of the nucleus carries genes through which hereditary features pass from one generation to the next.
Control of protein synthesis: Nucleus controls gene expression through the synthesis of different types of RNA and protein.
Formation of ribosomes: Nucleolus helps in the formation of ribosomes.
Pronucleus: Nucleus containing haploid chromosomes (n), at the stage before fertilization.
nucleoplasm
Amphinucleus: Nucleus with diploid chromosome. E.g., a nucleus of body cells.
Heminucleus: Nucleus carrying haploid chromosome. E.g., the nucleus of gametes.
Macronucleus and Micronucleus: The Nucleus that is larger in shape is the macronucleus and the smaller one is the micronucleus. (Found in Paramoecium)
Cytoplasmic Inclusion
Cytoplasmic Inclusion Definition: All the non-living substances produced during the metabolic activity of the cell, together are known as cytoplasmic inclusions.
In plant cells, these are called ergastic substances and in animal cells, they are called metaplastic bodies.
Types: These are divided into groups which are as follows—
Some main cytoplasmic inclusions: The major cytoplasmic inclusions are discussed below.
Reserve food: The end products of metabolism stored in the cell for future use are known as reserve food. They may be carbohydrates, proteins, fats, and oils.
Carbohydrates: These include starch, glycogen, and inulin. These are described below
Starch is a polysaccharide made up of glucose units. It is stored in plant cells,
Glycogen is a polysaccharide made up of glucose units. The stored glycogen in the animal body is called animal starch.
Inulin is a polysaccharide made up of fructose units.lt remains dissolved in the cell sap.
Protein: In animal cells, protein mainly forms the cytoskeleton but in plant cells, they are present as aleurone grains in seeds of castor, maize, wheat, etc.
Fats and oils: They are formed of fatty acids and glycerol. In plants, these are stored in the endosperm and cotyledons of seeds of mustard, nut, castor, etc. In animals, they are stored in the adipose tissue and liver cells.
Secretory materials: The secretory materials are stored in the form of zymogen granules, hormones, neurotransmitters, enzymes, and nectar.
Zymogens: These are inactive precursors of enzymes like pepsinogen (precursor of pepsin), trypsinogen (precursor of trypsin), etc. They appear like membrane-bound granules.
Hormones and neurotransmitters: These are chemical messengers that control various metabolic functions. Hormones are found in both plants and animals while neurotransmitters are found only in animals.
Enzymes: These catalysts are present in both plant and animal cells. They catalyze different metabolic reactions.
Nectar: In plants, nectar is secreted by nectar glands or special cells in flowers. It attracts the insects for pollination. A honey bee collects the nectar for the synthesis of honey.
Excretory products: Different types of metabolic end products are produced within plant and animal cells. In animal cells, the waste products are toxic, hence they are eliminated or excreted out of the body.
In plant cells, most of the excretory products are non-toxic and stored as cell inclusions within the cell.
Some of the excretory products of plant cells are—
Gums: Gums are hydrophilic, viscous, amorphous, colloidal substances, found in the stems of plants like acacia, google, and camphor.
Resin: Resins are excretory substances soluble in ether and alcohol. These are present in the leaves and stems of pine trees, opium plants, saal trees, etc. These are used as medicine and polish.
Latex: It is a milky, viscous, white colloidal substance found in specialized cells or ducts called laticifers of stems and leaves of banyan, papaya, jackfruit, etc.
Tannins: These are the nitrogenous wastes of plants as granular masses In the leaves and barks of tea, pine, date palm, hemlock, etc.
Essential oils: These are volatile oils found in petals (rose, jasmine), stems, and leaves (Eucalyptus).
Alkaloids: Different types of nitrogenous compounds, stored in the cells of different parts of the plant body are known as alkaloids. E.g., Quinine (root and stem of Cinchona), caffeine (in coffee), nicotine (leaves of tobacco), etc. These excretory substances have medicinal value.
Mineral crystals: Mineral crystals are formed by mineral salts. E.g., calcium salts are deposited in the form of calcium crystals in special parenchymatous cells of the plant body.
These are of two types—
Cystolith: Cystoliths are calcium carbonate crystals that appear like a bunch of grapes. They are deposited within special, enlarged cells of plants, called lithocysts. For, leaves of banyan, fig, and rubber have deposits of cystolith.
Raphide: Raphides are crystals of calcium oxalate. These are deposited within special, enlarged cells of plants, called idioblasts. E.g., leaves of Colocasia, water hyacinth, yam, onion.
Pigments: Few cells synthesize certain pigments like chlorophyll, anthocyanin, carotene, etc. that give color to the plant cells or organs like flowers, fruits, leaves, roots, etc. Similarly, in animal cells, different types of pigments are present like hemoglobin in the RBCs, melanin in skin and hair cells, etc.