- Anurfeate: Nucleus is absent Ex: RBC of mammal
- Mononucleate: It is very common. Usually the cell contains a single nucleus
- Binucleate: Two nuclei are present. Ex: cells of cartilage.
- Poly nucleate: Three to many nuclei are present. In animals poly nucleate cell is called "Syncytial cell". Ex: Syncytial cell of osteoblast.
- Cylindrical: Ex: Columunar epithelium.
- Horse shoe shape: Ex: Paramecium meganucleus.
- Tri lobed nucleus: Ex: WBC of mammals.
- Branched nucleus: Ex: Silk spining cell of insect larvae.
- Irregular nucleus: Ex: Glandular cell of insect.
- Nuclear membrane.
- Nucleo-plasm or karyolymph.
- Chromatin network.
- It gives protection to the genome.
- Helps in the reflection of DNA.
- During synaptic pairing in meiosis it attracts the homologous chromosomes.
- Granular zone
- Fibrillar zone
- Protenaceious part,
- Nucleolar associated chromatid.
- It is helpful in biogenesis of ribosomes.
- It plays a major role in mitosis.
- Nucleus plays a major role in the general metabolism of the cell
- It is helpful in the synthesis of ribosomes.
- It is helpful in the synthesis of RNA.
- It controls the synthesis of proteins.
- It is the seat of heredity.
- Mechanical support: E.R. will give mechanical support to cytoplasm. Hence it is called cytoskeleton.
- Intracellular transport: E.R. functions as circulatory system of the cell. It transport substance from one place to another place, in the cell it is called intracellular transport.
- Protein synthesis: ER. will provide surface for the attachment of ribosomes. These ribosomes will synthesise the proteins.
- Synthesis of lipoproteins: Smooth E.R. will synthesise lipids. In the Golgi complex the glycerides get associated with proteins produced by the E.R. Thus complex lipoproteins are formed.
- Detoxification: Smooth E.R. will detoxify internal, or external toxins. If toxins are more in the body more smooth E.R. will be produced.
- A.T.P. Synthesis: E.R. membranes are the sites of A.T.P, synthesis in the cell.
- Formation of other membranes: In the cell E.R. gives rise to.
a) Cisternae of Golgi apparatus.
b) Outer membrane of nucleus.
- Impulse conduction: In the muscle sarcoplasmic eticulum will release calcium which is responsible for the muscle action In 1926 "Porter" stated that E.R. membrane shows ionic grandients, and electric potential.
- The outer membrane of the nucleus will give buds. They unite to form annulate lamellae.
- Annulate lamellae will give rough E.R.
- From smooth E.R. golgi will form.
- Vesicles will give plasma lemma.
- According to GERL system Golgi will give rise to primary lysosomes. Thus there is an interrelationship among the membrane systems.
- Phospholipids: These substances have a composition which is in between the structure of phospholipids of endoplasmic reticulum and plasma membrane.
- Enzymes: ATP-ase, CPT-ase, transphorases, etc. enzymes are. present.
- Carbohydrates: Glucose, manose, galactose carbohydrates are seen.
- From E R: Beams & Kessel' in 1968 proposed that Golgi system cisternae arise from Endoplasmic reticulum.
- Rough E.R. produces protein which will be transfer to smooth ER.
- Vesicles are developed from smooth E.R.
- By the fusion of vesicles cisternae are formed. From the cisternae secretory vesicles are formed on the maturing face. (These sides are called "G.E.R.L" - Golgi Endoplasmic Reticulum Lysosome)
2) From nuclear membrane: In 1965 "Bouch" described the origin of golgi from the outer membrane of the nucleus. Vesicles are pinched off from the outer nuclear membrane and they are united to form cistemae.
- Proteins are produced by ribosome.
- They will be transmitted to smooth E.R.
- From there they are concentrated at Golgi complex.
- From the Golgi complex the secretory vesicles are formed.
Chemical Composition: Every lysosome will show hydrolytic enzyme. They are important in digestion of food such as 40 enzymes arc recognized in lysosome.
- It is a newly formed lysosome.
- It is formed from golgi.
- It forms from G.E.R.L, which means 'Golgi associated with Endoplasmic Reticulum will give Lysosome". This was stated by Dyson 1978.
- This is called original lysosome.
- A original lysosome units with a phagocytic or pinocync vesicle and forms a phagosome.
- In this phagosome the food is digested.
List of some hydrolytic enzymes seen in Lysosome:
Functions of Lysosomes:
- In 1857 Kolliker observed mitochondria and called them as sarco-somes.
- Flemming called them as Fila.
- Altmann in 1890 called them as Bioplasts.
- Benda gave the name mito-chondria.
- Porter & Palade described their electron microscopic structure.
- Mitochondria are present in all eukaryotic cells.
- Outer chamber
- Inner chamber.
- Luck stated free existing mitochondria will elongate and divide and new mitochondria are formed.
- Morrison stated mitochondria arise from either plasma membrane or endoplasmic reticulum.
- In the cytoplasm small particles may-be present they are called promitochondria they may give rise to mitochondria.
- In Bacteria & Mitochondria electron transport system is present in plasma membrane and in inner membrane respectively.
- Bacterial plasma membrane shows mesosomes, mitochondrial crystae can be compared with them.
- Both bacteria & Mitochondria will show circular D.N.A.
- In both bacteria and mitochondria ribosomes are reported.
- Both bacteria and mitochondria will produce AT.P. and R.N.A. Hence we consider the mitochondria might have originated from bacterial cell. In the cell mitochondria will function as semi-autonomous body.
- A.T.P. Synthesis: It is the power house of the cell. It brings oxidation of food. Hence Kreb's cycle reactions, electron transport system enzymes are located in mitochondria. By the oxidation of food energy is liberated in the form of A.T.P. (Oxidative phosphorelation takes place.)
- Yolk formation: Mitochondria are responsible for the fcri soiydk in the developing ovum Granules are formed in the matrix They oeconie large masses Mitochondrion is converted into yolk storing body.
- Mitochondrian sperm formation: When spermatid become? <pe'm mitochondria will form a spiral around the axial filament. This is called Neben-kem. It forms the middle piece of the sperm.
- Origin of new system: It is believed that some of the ceil organelles may originate from mitochondria.
- Heat production: In the oxidation of food ATP is released. Only 45% of the total energy is trapped in the form of ATP. The remaining 35% of ATP will come out as heat. (In birds and mammals this heat is useful for the maintenance of body temperature.).
- ATP released during respiration (because of mitochondria ) will take part in many biosynthetic paths of the cell.
- Nageli and Cramer called this membrane as cell membrane in 1855.
- In 1931 "Plowe" named this as plasmalemma.
- Modem cell biologists prefer to call it plasma membrane (According to De Robertis).
- Danielli & Davson in 1952 proposed molecular model of plasma membrane.
- Robertson proposed unit membrane concept in 1960.
- Human R.B.C. are kept in dilute solution (Hypotonic). Then it swells. It breakes and protoplasm will go out (Haemolysis). The remaining membrane is called Ghost. It is used for plasma membrane studies.
- Liver cell or the membrane surrounding the nerve fibre are used as a material for the study of plasma membrane.
- Outer layer is made by proteins....20 A°
- Middle layer is bimolecular lipid layer....35A°
- Inner layer is made by proteins ...20A°
- Danielli Davsons model: It shows thin lipid layer with protein absorbed on both the sides. The lipid contains polar heads pointing out sides and ion poiar parts run transversly. In 1954 Danielli modified this model and gave a new model.
- Robertson unit membrane concept: Robertson in 1959 described trilaminar structure of plasma membrane. It contains an outer and inner protein layers in between them a bimolecular lipid layer is present.
1) The unit membrane is 75A° thick.
2) The Outer and inner protein layers are 20A° thick.
3) In between them the lipid layer will show 35A° units.
4) The polar hydrophyllic ends of the lipid layer will face the proteins. Where as the hydrophobic ends of the lipids are away from the proteins.
- Fluid Mosaic model: In 1972 "Singer" & "Nicholson" proposed this model.
- Cell membrane is a mosaic of lipids and proteins.
- Lipids are arranged in a bilayer way. It forms the structural frame work of plasma membrane.
- Protein molecules are arranged in 2 ways.
1) Extrinsic proteins: These proteins are located adjacent to the outer and inner surfaces of the lipid layer.
- Hydrophobic end: It is water hating, non polar end.
- Hydrophilic end: It is water loving part. It is called polar end. It is present near the proteins.
- Structural pore: These are permanent openings.
- Dyanamic pores: They form during the intake of material.
- Protein channel pores: These are small channels of specific proteins through which some ions can diffuse.
- Modification of plasma membrane: To perform specialised functions plasma membrane will show some modifications.
- They are (a) Microvilli, (b) Inter digitations, (c) Desomosomes, tight junctions etc.
a) Microvilli: In certain parts the plasma membrane will show minute infloldings they are called microvilli. They show -1 mili micron diameter and 6 milli micron length. In some cases the villi are connected with endoplasmic reticulum. These microvilli are more in intestinal mucosa cells. The microvilli show cytoplasm with micro filaments. The microvilli will increase the absorptive surface of the intestinal epithelium.
b) Inter digitations: At some places the plasma membrane of adjacent cells will develop into finger like projections they are called inter digitations.
c) Desmosomes: The plasma membranes of adjacent cells become thicker in certain regions. On these thick areas fine, filaments are present. They are called tonbfilaments or tonofibrils. Such parts are called desmosomes. Desmosome is concerned with cell adhesion and maintenance of cell shape.
d) Terminal bar: It is a desmosome without tonofibrils. It is called terminal bar.
e) Zonula acculdens: These are special area of adjacent cells where the 2 plasma membranes fuse. These tight junctions are present below the apical boarder. It gives mechanical attachment between cells.
- Endocytosis: It is the process of by which large particles of food are engulfed. 1) Pinocytosis or cell drinking : Ingestion of liquid through plasma membrane is called pinocytosis.
- Micro pinocytosis is observed at submicroscopic level. When a liquid come nearer to plasma membrane, it forms a vesicles. It is called pinoc vesicle. After some time it is pinched off from the plasma membrane and becomes pinocytic vesicle in the cytoplasm
- Phagocytosis: The process of taking solid food or solid material through the cell membrane into the cell is called phagocytosis. Phagocytosis means to eat. It is first discovered by "Metknikoff
- Exocytosis: It is also called cell vomiting . The process of sending out products from the cell to the out side is called exocytosis or emeiocytosis.
- Active transport: If molecules or ions move against the concentrate gradient through plasma membrane, it is called active transport. For this energy is required. Now a days it is proved that carrier system is seen in the plasma membrane and it is responsible for active transport.
- It is believed that it develop de novo.
- It is formed by the assembly of lipids & proteins.
- It is believed that it develops from other membrane systems.
- It gives strength to the cell and forms cytoskeleton.
- Granular endoplasmic reticulum will produce proteins.
- Agranular endoplasmic reticulum will produce lipids.
- It forms the work bench for many biochemical reactions in the cell.
- In the central matrix of mitochondria respiratory enzymes are present. The take up Krebs cycle reactions.
- In the inner membrane of mitochondria electron transport enzymes are present.
- Mitochondria helps in the oxidation of the food material and liberates energy , Hence they are called power houses of cell.
- In the mitochondria a circular DNA is present. Hence mitochondria is also c. led semi autonomous body.
- Lysosome is helpful in the digestion of the food.
- At starvation lysosome will digest cell organelles.
- Lysosome can dissolve the cell. It is called suicide. Henc lysosomes are called suicidal bags of cells.
|Feature||Prokaryotic Cell||Eukaryotic Cell|
|2.||DNA||single, circular and naked||more than one and combined with proteins|
|5.||Division||amrtosis||mitosis or meiosis|
|6.||Ribosomes||70S(50S+30S scattered in cytoplasm||80S(60S+40S) Found attached to ER or free in cytoplasm.|
|9.||Chloroplasts||absent||present in plant cells, absent in animal cell|
|13.||Cell wall||non-cellulose||cellulose only in plants cells|
|14.||Respiratory enzymes||located in plasma membrane||enclosed in mitochondria.|
- In blue green algae cell shows a cell wall, enclosing protoplasm. In the protoplasm the peripheral coloured part is the chromateplasm and the central colorless part is the centroplasm. In the centroplasm there is DNA as the genetic material.
- Bacterial cell consists of a rigid cell enclosing protoplasm. The rigid cell is surrounded by slime layer or capsule. The protoplasm shows a peripheral plasma membrane which is often producing coiled mesosomes to carry respiration. The central part of the cell shows a long coiled thread like DNA. Protoplasm contains many ribosomes, fat bodies, volutin granules etc. The cells also show pili and flagella.
|Year||Names of contributor||Cytological contribution|
|1824||R.J.H. Dutrochet||Showed that all animals and plants composed of cells.|
|1826||Turpin||Reported the occurrence of cell division.|
|1831||R. Brown||Described the nucleus|
|1835||Felix Dujardin||Described protoplasm as ("Sarcode")|
|1838||M.J.Schleiden||Proposed "Cell theory"|
|1839||T.Schwann||Applied "Cell theory" to animals.|
|1840||J.E. Purkinje||Named the cell contents as Protoplasm.|
|1855||R.Virchow||Stated that all cells arise from pre-existing cell.|
|1863||Waldeyer||Chromosomes of cell|
|1871||F. Miescher||discovered nucleo-protein and nucleic acid.|
|1882||Strasburger||described mitosis in plant cells|
|1887||E.Van Benden||discovered centrioles.|
|1888||T.Boweri||described the centrioles.|
|1888||Waldeyer||Introduced the term chromosome.|
|1902||W.S.Sutton||Proposed "the chromosome theory" heredity.|
|1905||J.B.Farmer along with J.E.Moore.||Coined the term meiosis|
|1943||A.Claude||Isolated cell components like ribosomes, mitochondria and nuclei|
|1952||C. Du Duve||Identified hysosomes.|
|1953||J.D.Watson and F.H.C. Crick||Proposed the double helixmodel for the DNA molecule.|
|1959||S.Ochoa||Synthesis of polyribonuclotide in vitro.|
|1959||A.Kornberg||Synthesis of polydeoxiri-|
|1968||M.W.Nirenberg and H.G.Khorana.||Triplet genetic code.|
|1968||R.H.HoIley||discovery of base sequence of RNA|