Sunday, February 19, 2012

Cell organelles in eukaryotes


Name of the cell organelle
Functions
1.    Cell wall (Absent in animals and some protists. Present in bacteria, fungi, algae and plants).
-    Gives rigidity and support to the tissues and organs. Gives characteristic shape to the cells.
-    Maintains the balance of intracellular osmotic pressure with that of its surroundings.
2.    Cell coat (seen in many animal cells & protists)
Helps in the recognition of cells and adhesion of cells
3.    Cytoplasm
Includes living structures and non-living substances
4.    Plasma membrane
Similar to that of prokaryotes
5.    Cytoskeletons
Microfilaments
-     Contraction of muscle fibres. Help the movement of microvilli.
-     For the movement of plasma membrane during cell mobility and endocytosis.
Microtubules
Form the spindle apparatus during cell division. For the movement of chromosomes during cell division. Help in the maintenance of cell form and cell mobility.
Intermediate filaments
Form major structural proteins of skin and hair. Provide strength to the axons and dendrons of neurons. Maintain the shape of the cells and keep the nucleus and other organelles in place.
6.    Cilia
-    Serve to propel the cells through a fluid medium. Found in flame cells of flat worms, ciliata  of protista, larval bodies of many invertebrates, epithelium of respiratory tract, renal tubules etc.
7.    Flagella
-    Serve to propel the cells through a fluid medium. Found in many protists, motile algae, sperms of bryophytes, pteridophytes and animals; choanocytes of sponges; zoospores and gametes of thallophytes etc.
8.    Centriole
-     In animal cells, they function as centres for the organisation of spindle apparatus.
-     Responsible for the organisation and development of cilia and flagella.
-     Centrioles become the basal bodies of cilia and flagella.
9.    Endoplasmic reticulum
Granular E.R (Rough E.R or RER): Ribosomes present.
-    Acts as the intracellular transporting system. Synthesizes several enzymes. Helps in the synthesis of lipids and serum proteins. RER synthesizes protein with help of ribosomes. Helps the formation of middle lamella and nuclear membrane. Gives mechanical support to the cytoplasm.
-    SER brings about detoxification of drugs in the live cells.
Agranular E.R (smooth E.R or SER): Ribosomes absent.
10. Golgi apparatus (Golgisomes)
-    Secretory in function. Helps in the formation of cell membrane and middle lamella.
-    Vesicles of Golgi complex act as storage structures for proteins and lipids.
11. Lysosomes (Spherosomes in plants)
Intracellular and extracellular digestion
12. Cytoplasmic vacuoles (Surrounded by Tonoplast)
Sap vacuoles
Stores concentrate mineral salts and some nutrients.
Contractile vacuoles
Found in protozoans and some algal cells. Osmoregulation and excretion.
Food vacuoles
Found in the cells of protists, lower animals and phagocytes in higher animals. Digests nutrients with the help of enzymes present in food vacuoles.
Air vacuoles
Only in prokaryotes. Stores metabolic gases and thus regulate buoyancy of the cells.
13. Microbodies
Peroxisomes
Sites of photorespiration. Involved in b-oxidation of fatty acids. Prevent peroxides from acting on the cellular contents.
Glyoxysomes
Contains enzymes of glyoxylate cycle. Related to the metabolism of triglycerides. Glyoxylate cycle allows fungi, protozoans and plants to convert fat into carbohydrates. Also contain enzymes for oxidation of alcohols and alkanes. Germinating seeds of groundnut and castor contain glyoxysomes.
14. Ribosomes (aggregation of ribosome is called polysome or polyribosome or ergasome).
Protein synthesis. The mRNA which passes in between the two subunits is protected from the action of nuclease.
15. Mitochondria
Cell respiration. ATP synthesis. Protein synthesis due to the presence of DNA and ribosomes.
16. Plastids (in plants and Euglena)
Chloroplasts
Photosynthesis. Protein synthesis due to the presence of DNA and ribosomes.
Chromoplasts 
Contains pigments like carotene, xanthophylls etc. Gives colours to the flowers, fruits etc.
Leucoplasts
Amyloplast
Stores carbohydrates in the form of starch.
Aleuroplast (Proteinoplast)
Stores proteins
Elaioplast
Stores oils or fats.
17. Nucleus
Nuclear envelope (Karyotheca)
Surrounds the nucleus.
Nuclear sap (nucleoplasm or karyolymph)
Nucleolus and chromatin fibres are embedded in it. Contains proteins, enzymes, RNA, minerals etc.
Nucleolus
Biosynthesis of ribosome subunits. Helps in RNA synthesis.
Chromatin reticulum
Hereditary material.

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