Cell Inclusions



What are the cell Inclusions?

The cell inclusions are nonliving materials present in the cytoplasm. They are often called deutoplasmic substances. They may be organic or inorganic compounds, or both. The common cell inclusions are stored organic food materials, secretions and excretions, and inorganic crystals.




Inclusions in Prokaryotes :

In bacteria, reserve materials e.g. phosphate granules, cyanophycean granules and glycogen granules lie freely in the  cytoplasm as inclusion bodies or storage granules.Also found are some inclusion bodies e.g. poly__ b__ hhdroxybutyrate granules, sulphur granules, carboxysomes and gas  vacuoles which may be surrounded by a 2__ 4 nm thick, single layer non__ unit membrane. 

     Gas vacuoles are usually found in cyanobacterial, purple and green photosynthetic bacteria and a few other free__ floating aquatic forms ( planktomic). These are basically aggregates of a number of small, hollow cylindrical gas vesicles.The latter are permeable to atmospheric gases but not to water. Gas vacuoles help these  prokaryotes to keep floating on a near the surface of water so that they are able to trap sunlight for photosynthesis or for avoiding intense sunlight. 

      Major Inorganic inclusions in bacteria are polyphosphate granules ( volutin granules) and sulphur granules. These granules are also termed as metachromatic granules as they develop coloures when stained with basic dyes. Volutin granules, being phosphate polymers, act as storage reservoir for phosphate. Similarly, some bacteria store sulphur temporarily as sulphur granules either in periplasmic space or in special cytoplasmic globules. Such granules are specially formed when bacteria use hydrogen sulphide ( H2S) as electron donor during photosynthesis. 




Inclusions in Eukaryotes:

1: Reserve Food Materials: These include starch grains, glycogen granules, aleurone grains and fat droplets.

(i) Starch Grains: These occur in plant cells only. They are common in stronge organs, such as tubers and rhizomes. They are found in  chloroplasts and amyloplasts. The starch grains may occur singly ( wheat) or in group ( rich, oat), and are called simple or compound starch grains respectively. They may be spherical ( wheat), oval ( potato), polyhedral ( rice) in form. A starch grain consists of concentric or eccentric rings of starch deposited around a hilum of protein material. 

 (ii)  Aleurone Grains: These are protein materials deposited in special leucoplasts named aleuronoplasts of the plant cells. They occur in the outer endosperm cells of cereals, such as wheat , rice, maize grains. Aleurone grains are of four types:

(a) Amorphous,

(b) Protein matrix containing a crystalloid, e.g., outer aleurone layer of endosperm in wheat ,maize , barley grains


(c) Protein matrix with globoid, 

(d) Protein matrix having both crystalloid and globoid inclusion, e.g., endosperm ( e.g., Castor, Conont ) or cotyledons ( e.g., Groundnut, Mustard).

 (iii) Glycogen Granules: These are spherical or rosette__ shaped polysaccharide particles stored in the liver and muscle cells of animals.

(iv) Fat Droplets: These occur in fat__ storing cells, the adipocytes, of animals. An adipocyte may contain one to several fat droplets. The latter push the cytoplasm to the cell periphery where nucleus also lies. The fat droplets also occur in the cells of the endosperm of castor and coconut and in the cells of the cotyledons of groundnut and mustard seeds.



2: Secretions and Excretions: These include muscu in animal cells, and essential oils, alkaloids,  resins, gums, tannins latex, etc. in plant cells.

(i) Latex:It is a crystallo_ colloid fluid secreted by laticifers of two  types latex cells, e.g., Banyan, calotropis and latex vessels, e.g., poppy, rubber plant.Latex can be watery, milky or coloured. Latex of Hevea brasilliensis yields rubber.

(ii) Gums: They are the degradation products of cell wall.

(iii) Gum resins: It is a mixture of gum and resin.

(iv) Resins: They are acidic oxidation  products  of essential  oils which are soluble in alcohol, turpentine but insoluble in water.


(v) Tannins: They are astringent, acidic, phenolic compounds related to glycosides found in leaves, e.g., tea, bark walnut fruit, e.g., Betal nut.


(vi) Nectar: It is sugary secretion of flower part for attaching insects and other animals for pollination. 

(vii) Pigment granules  : Melanin and lipochromes are two types of pigment granules producing by pigment producing chromatophores viz. melanophores and lipophores. Melanin is brownish or blackish while lipochromes are organe, red or yellow in colour.

3: Inorganic Crystals: These occur in plant cells. The crystals of calcium ( calcium carbonate, calcium sulphate, calcium oxalate) and silica are common. Crystals occur in different formations__ 

(a) Cystolith:It consists of calcium carbonate crystals deposited around a cellulose framework, as in epidermal cells of Momordica, hylodermal leaf cells of Ficus bengalensis.
 
( b) Crystal Sand:  It is a powdery mass of calcium oxalate as in Atropa.

( c) Raphides: These are needle__ like crystals of calcium oxalate in Lemna, Eichhornia.

( d) Sphaeraphides: These are star_ shaped groups of calcium oxalate crystals in Colocasia, Chenopodium, etc. 

 ( e) Prismatic crystals  of calcium oxalate occur in the dry scales of Allium cepa.

4: Pigment Granules:  These are found in special cells, called chromatophores, present in the skin ( dermis) of vertebrates ( fishes, amphibians and reptiles).The chromatophores are of two types: melanophores having brown or black pigment, and lipophores containing red, yellow and orange pigments. Birds and mammals have a pigment in the feathers and hair.In the human skin, the pigment __ containing cells occur in the deeper epidermal cells.

Endomembrane System: 

The endomembrane system of a eukaryotic cell consists of nuclear envelope, endoplasmicreticulum,  Golgia apparatus, lysosomes, vacuoles and plasma membrane. These membranes are related through physical continuity or by transfer of membrane systems as transport vesicles. The membranes are not similar in structure and function. Their thickness, molecular composition and metabolic activities vary at different times.

        Mitochondria and chloroplasts though enclosed by membranes,  are not include in endomembrane  system.Their membranes are not formed by ER, but by free ribosomes found in the cytosol and by   ribosomes present within them.


Interdependence of Cytoplasm and Nucleus: 

Both   cytoplasm and nucleus are necessary for the normal activities of a cell, but the exact role of each in the metabolism   of the whole is not fully clear yet. In general,  the cytoplasm is the seat of  metabolic  processes including synthesis of proteins,  formation of enzymes and oxidation. This is also a storehouse of the raw materials needed for metabolism in both the cytoplasm and the nucleus. The nucleus controls inheritance. It regulates the cytoplasmic activities by guiding the synthesis of enzymatic proteins. It maintains the cytoplasm by directing the formation of structural proteins.

Differences between Cytoplasm and Nucleoplasm

  Cytoplasm 

1): It is part of the protoplasm outside the nucleus. 

2): It is enclosed by a single unit membrane, the cell membrane or plasmalemma. 

3): Plasmalemma may have a few simple pores that lead into the endoplasmic reticulum. 

4): Plasmalemma does not bear ribosomes. 

5): Cytoplasmic matrix is an aqueous, nearly transparent, structureless ground substance. 


6): Under the free surface of th cell, cytoplasm is gel_ like, forming relatively stiff ectoplasm. 

7): Cytoplasm contains several types of organelles. 

8): Cytoplasm undergoes nonstop cyclosis.

9): Cytoplasm contains a system of membranes called ER.

10): Cytoplasm forms a greater part of the cell.

11): Cytoplasm provides raw materials and energy to the cell, including nucleus. 


Nucleoplasm 

1): It is the protoplasm that forms the nucleus. 

2): It is bounded by two unit membranes that together form the nuclear envelope. 

3): Nuclear envelope has numerous complex pores, each fitted with a pore complex and leading into the nucleoplasm. 

4):  Nuclear envelope bears ribosomes on the cytoplasmic surface of its membrane. 

5): Nuclear matrix is a network of protein__ containing fibrils.

6): Matrix forms a dense nuclear lamina closely associated with the entire nuclear envelope for support. 

7): Nucleoplasm contains only 3 types of organelles: matrix, chromatin and nucleolus.

8): There is no cyclosis in the nucleus. 

9): There are no membranes within the nucleus.

10): Nucleoplasm forms only a small part of the cell.

11): Nucleoplasm provides information for maintenance and activities of the cytoplasm.


































































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RNA                    Nucleic Acids




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