Cell The Unit of Life

Cell : The Unit of Life INTRODUCTION (iii) Cells perform Vital activities of an organism. Cell is a basic of life and it is considered as structural (vi) Each cell is unit of heredity. and functional unit of an organism. Robert Hooke (1665) discovered cell. He first observed the cell in (v) New cell arises from pre existing cells "Omnis cellula e cellula". It is called cell lineage theory. This concept a piece of dead cork cells. He described cell in his book "Micrographia". was given by Rudolph virchow (1855). Leeuwnehoek (1674) first observed animal cell and used the term "Animalcule" for it. OBJECTIONS : The study of cell structure is called cytology. (1) Bacteria and cyanobacteria do not bear nucleus and The study of cell structure, function & Reproduction membrane bound cell organelles. is called Cell biology. (2) Viruses are acellular and do not contain cellular Term 'cytology' was coined by 'Hertwig' who wrote machineary. a book entitled 'cells & tissues'. Robert hook is (3) RBCs and sieve tube cells live without nucleus. known as 'father of cytology'. Cell Theory : Malthias Schleiden (German botanist) and schwann (German Zoologist) jointly proposed cell theory in 1839. CELL - AN OPEN SYSTEM : An open system is one which is separated from its surrounding by a boundary that allows transfer of Its main features are as follows material in and out of the cells. Cell is an open system (i) All living organism consist of cells and their products. because it recieves a number of materials & energy (ii) All cells are structurally and metabolically similar. from outside and liberates energy as heat. 1 Cell : The Unit of Life 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 1. 2. 3. 4. 5. 6. 7. 8. 9. Difference between Prokaryotic and Eukaryotic Cell Prokaryotic cell Eukaryotic Cell The cell size is small (0.1 – 0.5 um.) 1. The cell size is comparatively larger (0.5-100 um). An organized nucleus is absent instead a 2. An organized nucleus is found. It is nucleoid is found. differtntiated into nuclear envelope, chromatin one or more nucleoli and nucleoplasm. Cell wall if present, contains muramic acid. 3. Cell wall, if present, muramic acid in absent DNA is naked, it means histones absent 4. DNA is found with histones. DNA lies freely in the cytoplasm. 5. Most of the cell DNA is found in the nucleus. A small quantity is also found in thhe plastids and mitochondrai. DNA is circular. 6. Nuclear DNA is linear whereas Extra nuclear DNA is circular. Trancription and translation take place in the 7. Transcripition occurs in the nucleus while cytoplasm. translation takes place in the cytoplasm. Cytoplasm does not show cyclosis. 8. Cytoplasm usually shows cytoplasm. Membrane bound organelles like 9. Mithochondria, ER, Golgi apparatus & mitchondria, Golgi apparatus, ER, microbodies including lysosomes are present in Lysosomes and other microbodies are cell of organism. absent. Microtubules and microfilaments are 10. MIcrotubules and microfilaments are present. commonly absent. 70S types of Ribosomes are found. 11. Ribosomes are of 80S types.70S ribosomes are found in mitochondria and plastids. Centriole is also absent 12. Centriole is present in animals & lower plants Ex:- Bacteria, Cyanobacteria, Mycoplasma. 13. Ex:- Protists, Fungi, Plants and Animals. Differences between PLant ande Animal Cells Plant cell Animal cell A plant cell has rigid wall on the outside. 1. A cell wall is absent. Plastids are found in plant cells 2. Plastide are usually absent. A mature cell has a largecentral vacuole. 3. An animal cell may have many small vacuoles. Nucleus lies on one side in the peripheral 4. Nucles usually lies in the centre. cytoplasm due to central vacuole. Centrioles are usually absent. 5. Centrioles are found in animals cells. Golgi apparatus consists of number of 6. Golgi apparatus is either localised or diffused distinct & unconnected units called & consits of a well connected single complex. dictyosomes. Reserve food is generally starch and fat. 7. Reserve food is usually glycogen and fat. Adjacent cells may be connected through 8. Adjacent cells are connected through a number plasmodesmata. of cell junctions. Cytokinesis occurs by cell plate. 9. Cytokinesis takes place by cleavage. 2 Cell : The Unit of Life could be 3 to 5 m. The largest isolated single cell is the egg of an ostrich. Among multicellular organisms, human red blood cells are about 7.0 ìm in diameter. Nerve cells are some of the longest cells. Cells also vary greatly in their shape. They may be disc-like, polygonal, columnar, cuboid, thread like, or even irregular. The shape of the cell may vary with the function they perform. SHAPE AND SIZE OF CELLS Cells differ greatlyin size, shape and activities (Figure). For example, Mycoplasmas, the smallest cells, are only 0.3 m in length while bacteria STRCUTUREOFAPROKARYOTICCELLS The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms). They are generally smaller and multiply more rapidly than the eukaryotic cells. Diagram showing different shapes of the cells 1. Shape and size of cell : They may vary greatly in shape and size. The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral). 2. Cell Envelope and its Modifications : Most prokaryotic cells, particularly the bacterial cells, have a chemically complex cell envelope. The cell envelope consists of a tightly bound three layered structure i.e., the outermost glycocalyx followed by the cell wall and then the plasma membrane. Although each layer of the envelope performs distinct function, they act together as a single protective unit. Bacteria can be classified into two groups on the basis of the differences in the cell envelopes and the manner in which they respond to the staining procedure developed by Gram viz., those that take up the gram stain are Gram positive and the others that do not are called Gram negative bacteria. 3 Cell : The Unit of Life 3. 4. 5. 6. Glycocalyx differs in composition and thickness 7. among different bacteria. It could be a loose sheath called the slime layer in some, while in others it may be thick and tough, called the capsule. The cell wall determines the shape of the cell and provides a strong structural support to prevent the bacterium from bursting or collapsing. The plasma membrane is semipermeable in nature and interacts with the outside world. This membrane is similar structurally to that of the eukaryotes. 8. Nucleoid : All prokaryotes have a cell wall surrounding the cell membrane. The fluid matrix filling the cell is the cytoplasm. There is no well-defined nucleus. The genetic material is basically naked, not enveloped by a nuclear membrane. In addition to the genomic DNA (the single chromosome/circular DNA). Plasmid : Many bacteria have small circular DNA outside the genomic DNA. These smaller DNA are called plasmids. The plasmid DNA confers certain unique phenotypic characters to such bacteria. One such 9. character is resistance to antibiotics. In higher classes you will learn that this plasmid DNA is used to monitor bacterial transformation with foreign DNA. Mesosome : A special membranous structure is the mesosome which is formed bytheextensions ofplasma membrane into the cell. These extensions are in the form of vesicles, tubules and lamellae. They help in cell wall formation, DNA replication and distribution to daughter cells. They also help in respiration, secretion processes, to increase the surface area of the plasma membrane and enzymatic content. In some prokaryotes like cyanobacteria, there are other membranous extensions into the cytoplasm called chromatophores which contain pigments. Flagella : Bacterial cells may be motile or non-motile. If motile, they have thin filamentous extensions from their cell wall called flagella. Bacteria show a range in the number and arrangement of flagella. Bacterial flagellum is composed of three parts – filament, hook and basal body. The filament is the longest portion and extends from the cell surface to the outside. Pili and fimbriae : Besides flagella, Pili and Fimbriae are also surface structures of the bacteria but do not play a role in motility. The pili are elongated tubular structures made of a special protein. The fimbriae are small bristle like fibres sprouting out of the cell. In some bacteria, they are known to help attach the bacteria to rocks in streams and also to the host tissues. Ribosomes : In prokaryotes ribosomes are associated with the plasma membrane of the cell. They are about 15 nm by 20 nm in size and are made of two subunits - 50S and 30S units which when present together form 70S prokaryotic ribosomes. Ribosomes are the site of protein synthesis. Several ribosomes may attach to a single mRNA and form a chain called polyribosomes or polysome. The ribosomes of a polysome translate the mRNA into proteins. Inclusion bodies: Reserve material in prokaryotic cells are stored in the cytoplasm in the form of inclusion bodies. These are not bounded by any membrane system and lie free in the cytoplasm, e.g., phosphate granules, cyanophycean granules and glycogen granules. Gas vacuoles are found in blue green and purple and green photosynthetic bacteria. EUKARYOTIC CELLS : The eukaryotes include all the protists, plants, animals and fungi. In eukaryotic cells there is an extensive compartmentalisation of cytoplasm through the presence of membrane bound organelles. Eukaryotic cells possess an organised nucleus with a nuclear envelope. In addition, eukaryotic cells have a variety of complex locomotory and cytoskeletal structures. Their genetic material is organised into chromosomes. All eukaryotic cells are not identical. Plant and animal cells are different as the former possess cell walls, plastids and a large central vacuole which are absent in animal cells. On the other hand, animal cells have centrioles which are absent in almost all plant cells . 4 Cell : The Unit of Life Diagram showing : (a) Plant cell (b) Animal cell 5 Cell : The Unit of Life Primary wall : Outermost layer, thin elastic composed of cellulose, hemicellulose & pectin. Secondary Wall Cell wall : (S1, S2, S3) Tertiary wall Rigid, thick & composed of cellulose, hemi–cellulose, Pectin. (absent in meristem cells) : Present only in tracheids of Gymnosperm. Composed of hemi cellulose & xylan. Middle lamella : Common layer between two cells. * Cell wall was discovered by Robert–Hooke. STRUCTURE OF BIOMEMBRANES : * Outer most but dead boundary of plant cell is cell * wall. * Bacteria included in plants because they have cell Fluid mosaic model : By Singer & Nicolson (1973) wall. * * This is latest & most widely accepted model for the structure of plasmalemma. * According to fluid mosaic model protein are arranged in phospholipid layer as mosaic pattern. * Thus membrane is termed as "protein icebergh in a sea of phospholipid" or "Gulab Jamun (protein) in a concenterated solution (phospholipid) of sugar". Fruits become soft and juicy due to dissolve of middle lamella. * * Middle lamella is consist of Ca & Mg pectates (Plant cement).Amount of Ca is more. Cellulose is a main constituent of cell wall but addition to cellulose – Hemicellulose, cutin, Pectin, Lignin, Suberin are also presents in cell wall. * Cell wall worked as frame or protective layer of cell. * Cellulose microfibrils and macrofibrils arranged in (1) Phospholipids : * Phospholipid is the main component of cell membrane because it forms continous structural frame of cell membrane. Main type of phospholipids are phosphatidyl serine, phosphatidyl choline (Lecithin), P-ethanol amine (cephalin) * Phospholipid layer provides fluidity to plasma membrane because phospholipids are rich in unsaturated fatty acid which are liquid in nature. * Cholesterol is also present in plasmamembrane. Cholestrol are more rigid than phospholipid. So it helps in stability of membrane structure. * Cholesterol is absent in membrane of prokaryote. Thus Hopanoides (Pentacyclic sterol) provides stability to prokaryotic cell membrane. layers to form skeleton of cell wall. In between these layers other substances like pectin,hemicellulose may be present. These form matrix of cell wall. All these models are rejected because they fails to explain the elasticity and selective permeability of plasmalemma. 6 (2) Proteins : * Two types of protein are present in plasma membrane. (a) Integral or intrinsic protein (70%) * * * * as carriers for the transport of materials. Spectrin are helical type of extrinsic protein founds on cytosolic These protein are tightly binds with phospholipid. Thus not easily released from membrane. face of membrane and attached to intrinsic protein. Some intrinsic protein are confined in lipid bilayer * (Stable protein). However phospholipid bilayer has fluid property but Some integral proteins traverse the complete thickness of membrane. These type of protein are called as tunnel protein which passage water soluble material across the membrane. molecule (Flip Flop means exchange of molecules * Some intrinsic protein extending from outside to inside are called as transmembrane protein eg. glycophorin, porins. Porins founds in outer mitochondrial * Membrane and Bacterial Memberane. (b) Peripheral or extrinsic protein (30%) * Cell : The Unit of Life Some protein like permeases and translocase function These are superficially arranged on outer side and can be seperate easily. These protein have enzymatic activity. Extrinsic protein can move freely on membrane structure. Spectrins are part of cytoskeleton. no evidence of flip flop mechanism for protein from one monolayer with those in the monolayer on the other side). Rotational diffusion and lateral diffusion of protein and lipids is possible in membrane. Absence of flip flop movement detected by electro spin resonance (ESR) spectroscopy. Lipids – 40% (Phospholipids, cholesterol, glycolipids) Proteins – 58–59% (Arginine, Lysine rich) Carbohydrates – 1–2% 7 TRANSPORT THROUGH PLASMA MEMBRANE * Plasma membrane now consider as selectively or differentially permeable because it allows certain solutes to pass through it and prevents others. One of the most important functions of the plasma membrane is the transport of the molecules across it. The membrane is selectively permeable to some molecules present on either side of it. Many molecules can move briefly across the membrane without any requirement of energy and this is called the passive transport. Neutral solutes may move across the membrane by the process of simple diffusion along the concentration gradient, i.e., from higher concentration to the lower. Water may also move across this membrane from higher to lower concentration. Movement of water by diffusion is called osmosis. As the polar molecules cannot pass through the nonpolar lipid bilayer, they require a carrier protein of the membrane to facilitate their transport across the membrane. A few ions or molecules are transported across the membrane against their concentration gradient, i.e., from lower to the higher concentration. Such a transport is an energy dependent process, in which ATP is utilised and is called active transport, e.g., Na+/K+ Pump. CYTOPLASM * Term "Cytoplasm",was given by Strasburger for the part of cell, presents between the nucleus and cell membrane. Cytoplasm can be devided into two parts. * Ground plasm / Hyaloplasm / Cytosol Liquid matrix of cytoplasm except organelles * Trophoplasm Part of cytoplasm containing organelles & non living Inclusions. CELL ORGANELLES Permanent Metabolically active and living structures of cytoplasm are called organelles. * * Cell : The Unit of Life In higher animals maximum mitochondria are found in flight muscles of birds. Mitochondria can make its shape as ellipsoidal, oval, spherical or spiral. Mitochondria * Power house of cell or ATP-mill in cell * Cell within cell/second largest organelle * Cell furanaces or storage batteries * Most busy and active organelle in cell * Semi autonomous cell organelle. STRUCTURE : * Mitochondria is covered by double unit membrane. Outer membrane has more phospholipids (Phosphatidyl choline) and cholesterol as compared to inner membrane. * Inner membrane is folded into a number of finger like cristae. Cristae are tubular finger like but in fungi cristae are plate like. * In metabolicallyactive mitochondria number of cristae is higher. * Many electron carrier cytochromes are arranged in a definite sequence in Inner membrane of mitochondria, which forms Electron transport system (ETS) for oxidative phosphorylation. * Inner membrane is studded with pin head particles called oxysomes or elementary particles or F1 – F0 particles ( 104 to 106 in number). * Head of Oxysomes composed of ATPase (ATP synthase) enzymes and concerned with Oxidative phosphorylation * Matrix have a complete protein synthesis apparatus (Ribosome- 70-s, DNA, few RNA's & enzymes) so mitochondria called as semi autonomous cell organelles. * Enzymes for replication and transcription of DNA like DNA- polymerase and RNA- polymerase are found in mitochondrial matrix. MITOCHONDRIA * 5 lakhs mitochondria in an Amoeba Chaos Chaos. * All the mitochondria present in a cell are collectively called chondriome. * Usually plant cells have fewer mitochondria as compared to animal cell. 8 Cell : The Unit of Life FUNCTIONS OF MITOCHONDRIA (1) Most of the oxidative metabolism andATP production occurs in mitochondria, thus mitochondria are the power house of cell, where organic compounds are broken down to release & store metabolic energy in the the form ofATP molecules. (Resp. metabolism). Structure of mitochondrion (Longitudinal section) (2) Mitochondria help in vitellogenesis in oocytes. (3) In cytoplasmic inheritance. GOLGI COMPLEX : * * * Discovered by C.Golgi (1898) - In nerve cells of owl and named "internal reticular apparatus" (Golgi * body first observed by L.S. George) Convex surface of cisternae which is towards the nucleus is called cis- face or forming face. Concave surface of cisternae which is towards the membrane is called Transface or maturing face. Golgi body also named as * Golgi body * Golgi complex * Dalton complex * Dictyosome STRUCTURE Golgi complex is made up of four parts – (2) Tubules :– These are branched and irregular tube like structures associated with cisternae. (3) Vacuoles :– Large spherical structures associated to tubules. (1) Cisternae :– These are unbranched saccules likes (4) Vesicles :– Spherical structures arise by budding smooth E.R., many cistenae are arranged in a stack. from tubules. Vesicles are filled with secretory Dense opaque material inside cisternae is called materials. Node s. 9 (2) (3) (4) (5) Cell : The Unit of Life Synthesis of cell wall Material (Polysaccharide synthesis) Cell plate formation (Phragmoplast) during cell formation. Formation of acrosome during spermiogenesis. (formation of male gametes) Vitelline membrane of egg is secreted by golgi body. LYSOSOME * Christian De Duve (1955) discovered lysosome as cell organelle and also named Lysosomes. * With the exception of mammalian RBC they were reported from all cells. Golgi apparatus * In plant cells large central vacuole functions as Lysosome. So in higher plants lysosomes are less * Golgibody1 is single membrane bound cell organelle. frequent. But number of lysosomes is high in fungi. * About 60% proteins and 40% phospholipid occur in * Lysosomes are spherical bag like structures golgi body. (0.1-0.8 m) which is covered by single unit membrane. They are larger in Phagocytes (WBC) FUNCTIONS : (0.8 to 2 m). (1) Cell Secretion :– Chief function of golgi body is * Lysosomes are filled with 50 different type of digestive secretion (export) of macromolecules. enzymes termed as Acid hydrolases. Secretion involve three steps : (a) Golgi body recieves the materials from E.R. through FUNCTIONS (1) Heterophagy:– This is digestion of foreign materials it's cis - face. received in cell by phagocytosis and pinocytosis. (b) These materials are chemicallymodified bygolgi body. (2) Autophagy :– Digestion of old or dead cell (For e.g. glycosidation (glycosylation) of proteins organelles. Autophagy also takes place during and lipids takes place in golgi body and it yields starvation of cell. glycoprotiens and glycolipids). (3) Extracellular digestion :– (c) After chemical modifications materials are packed in Lysosomes of osteoclast (bone eating cells) dissolve vesicles. These vesicles are pinched off from trans unwanted part of bones. face of golgi body and discharged out side the cell (Extracellular digestion also occurs by fungal lysosomes.) (Reverse pinocytosis) * Golgi complex involves secretion ofzymogen granules (5) Cellular digestion (Autolysis) :– Sometimes all lysosomes of a cell burst to dissolve the cell completely. from pancreas, secretion of lactoprotein from Old cells are removed by autolysis. unwanted organs mammary Glands. of embryo are destroyed by autolysis Cathepsin of * The secretion of hormone by endocrine glands is lysosome digests the tail of tadpole of frog during mediated through golgibodies. metamorphosis. * Biogenesis of Lysosome Lyosomes originates from All the macromolecules which are to be sent out side G E R L - (Golgi associated Endoplasmic Reticulum the cell, move through the golgi body. So golgi body from which Lysosomes arise). is termed as “Director of macromolecular traffic E.R. Golgi body  Lysosome in cell” or middle men of cell. 10 Cell : The Unit of Life (3) Tubules - These are irregular, often branched tubes ENDOPLASMIC RETICULUM : bounded by membrane. Tubules may free or * "Garnier" (1897) first observed them and called associated with cisternae. Ergastoplasm. E. R. name proposed by "Porter" (1961). (Credit for discovery of ER goes to Porter) * Structure of E.R. is like the golgi body but in E.R. Components of E.R. :– (1) Cisternae - These are long flattened and unbranched units arranged in stacks. * (2) Vesicles - These are oval membrane bound structures. cisternae, vesicles and tubules are isolated in cytoplasm and these do not form complex. Golgi body is localised cell organelle while E.R. is widespread in cytoplasm. E.R. is often termed as “System of Membranes” Rough E.R. (Granular) (1) 80s ribosomes binds by their larger Smooth E.R.(Agranular) (1) Ribosomes and Ribophorins absent subunit, with the help of two glycoproteins (Ribophorin I and II) on the surface of Rough E.R. (2) More Stable structure (2) Less Stable structure (3) Mainly Composed of cisternae and vesicles (3) Mainly composed of tubules. (4) Abundantly occurs in cells which are actively engaged in protein synthesis (4) Abundantly occurs in cells concerned with glycogen and lipid metabolism. e.g. liver, pancreas, Goblet cells. e.g. Adipose tissue, Interstitial cells, Muscles,Glycogen storing liver cells, and adrenal cortex. 11 Cell : The Unit of Life (6) Formation of lysosomes, Golgi–body & Micro– FUNCTIONS OF E.R. bodies. All the organelles are form by E.R. which (1) Mechanical support :– Microfilaments, have membrane except chloroplast and mitochondria Microtubules and E.R. forms endoskeleton of cell. (semi autonomous organelles) (2) Intracellular exchange :– E.R. forms intracellular conductingsystem.Transport of materials in cytoplasm PLASTIDS from one place to another may occurs through the * The term "Plastid" first used by Haeckel . E.R. * At some places E.R. is also connected to P.M. So Types of Plastids : E.R. can secrete the materials outside the cell. (1) Chromoplasts:– These are plastids, which contain (3) Rough E.R. :– Provides site for the protein synthesis, different types of pigments (carotenes, Xanthophylls because rough E.R., has ribosomes on its surface. etc.). Chlorophylls either absent or occur in very less (4) Lipid Synthesis :– Lipids (cholesterol & amount. Chromoplasts occurs mainly in pericarp phospholipids) synthesized by the agranular portion and petals. Red colour of chillies and red tomatoes is of E.R. (Smooth E.R.). The major lipids synthesized due to the red pigment "Lycopene" of by S. E. R. are phospholipids and Cholesterol. chromoplasts,. Lycopene is a type of carotene. (5) Formation of nuclear membrane :– Fragmented Yellowish - orange colours of fruits are due to vesicles of disintegrated nuclear membrane and ER -carotene, -carotene and –carotene.–carotene elements arranged around the chromosomes to form is precursor of vitamin-A. Richest source of a new nuclear membrane during cell division. -carotene are carrot roots. (2) Chloroplasts :– Green plastids with chlorophylls and other photosynthetic pigments. (3) Leucoplasts :– These store food in different forms * like starch (Amyloplasts), Fat and oil (Elaioplasts) and protein (Aleuroplasts). Pigments and lamellar structure absents in Leucoplasts. Generally occurs in non green and underground plant cells. * Chloroplast is a double membrane bound cell organelle, and is the largest organelle of cell. (4-6 m x 1-3 m). (largest component is nucleus) * Internally chloroplast contains stroma (Matrix) and thylakoids or lamellae. Matrix part of chloroplast contains circular or rarely linear DNA, RNA, 70-s Ribosomes, starch grains, enzymes of calvin cycle or dark reaction. Rubisco is the most abundant enzyme on the earth. It made 16 % protein of the chloroplast. The number of chloroplast in cell of higher plants 20-40.(One in chlamydomonas) 12 Cell : The Unit of Life * Thylakoids (Term by Menke 1962) are membrane lined flattend sacs, which forms stacks called granum (Plu. grana). Each chloroplast contains about 20-100 granum. Fret channel or stromal thylakoids is connection between two granum. Photosynthetic pigments (chlorophylls) are located in the thylakoid membranes. * Chloroplasts has their own genetic system & complete protein synthesis machinary (ds-DNA, RNA, Ribosomes, enzymes, Amino Acids), thus (b) Kinetosome or basal granule or Blepheroplast chloroplasts are called as semiautonomous or Basal body : It is membraneless structure, lies organelle of the cell. immediately below the plasmamembrane. Basal body exhibit cart wheel structure similar to centriole. FUNCTIONS : (9 triplet fibriles connected to a central hub in basal (1) Photosynthesis : The chloroplasts trap the light body). energy of sun and transform it into the chemical energy * Arrangement of microtubules is 9 ( triple) +0. in the form glucose. In basal granule there occurs 9 microtubules on periphery and each microtubule is composed of three (2) Balancing of O2 & CO2 in nature. tubules i.e. A-tubule, B-tubule and C-tubule (3) Chloroplasts impart the pleasing greenary to the earth. * Central part of basal granule is composed of semisolid (4) Chloroplasts store vitamin K, E, Rubisco protein and cytosol called "Central Hub". Fe etc. * Microtubules connected to central hub with the help of protein fibres called primary fibres or spokes. CILIAAND FLAGELLA : * Secondary fibres connect microtubules with each * Cilia & Flagella are mechanical, hair like cellular other. appendages and locomotory structure. Flagellar (c) Rootlet or Rhizoplast : This is a conical bundle of protein fibers which arises from basal bodyto different apparatus is consist of following Parts. directions. Rootlet have dark bands composed of (a) Shaft or ciliary part : It is projecting hair like part ATPase. of ciliary appartus. Cilium is composed of 11 * Cilia and Flagella are simialr in structure but some microtubules. (9 doublet + 2 singlet) differences may observed – * Bundle of microtubules is called as axonema. Nine Cilia Flagella microtubules are peripheral and each composed of 1. The cilia are small in 1. Flagella are long two small tubules i.e. A tubule with two arms and size (5–10m) (up to 150 m) B-Tubules without arms. 2. Number of cilia per 2. Few in number * Microtubules is consists of a contractile protein tubulin similar to actin of muscles. * The central tubules are connected by bridges and is also enclosed by a central sheath, which is connected to one of the tubules of each peripheral doublets by radial spoke. Thus there are nine radial spokes. The peripheral doublets are also interconnected by linkers. cell is very large. 3. Cilia beat in a 3. Flagella beats coordinated manner independently (sweeping or (Non coordinated pendular move) manner) 4. They take part in 4. Flagella involved locomotion,attachment, only in locomotion feeding and sensation. 13 CENTROSOME : * * Centrosome was discovered by Benden. Boveri named as centrosome. Centrosome is absent in higher * plants. Two centrioles located just outside the nucleus and lie at right angle (90°) to each other. Cytoplasm which * surrounds centrioles called as " Centrosphere". Centrioles and centrosphere collectively called * centrosome or Microcentrum or diplosome. Cell : The Unit of Life Each centriole is surrounded by peri centriolar mass, which is called as massules or crown or satellite. Centrioles are membraneless elongated structure which exhibit cart wheel structure (Just like Basal body of cilia). Basal body is also a type of centriole. Centriole mainly consist of 9 triplet fibers of tubulin. (9 + 0 arrangement) Centrioles are self duplicating units, which contains DNA, RNA and protein synthesis machinary. Function:– In animal cells centrioles play important Types of Ribosomes :– role in initiation of cell division by arranging spindle (1) Eukaryotic ribosomes:– 80 s - Occur in cytoplasm fibres between two poles of cell. The location of of eukaryotic cells. centrioles during cell division decides the plane of (2) Prokaryotic ribosomes :– 70 s - Occur in cytoplasm division. The plane of division is always at right angle of prokaryotes, and also in mitochondria, and to the long axis of spindle. Thus centrioles is also Chloroplast of eukaryotes. (55 S ribosome present termed as "cell centers". in mitochondria of mammals) * Each ribosome composed of two subunits i.e. larger RIBOSOMES (ENGINE OF CELL) : and smaller subunits. Larger subunit is dome shaped * Claude first observed them. Palade (1955) coined and smaller unit is ovoid. Smaller subunit has a the term Ribosome. platform, a cleft, a head and a base. The larger * In plants Robinson and Brown (1953) first observed subunit has a protuberance, a ridge and a stalk. them in bean roots. Larger subunit also contains a tunnel which opens in cavity of E.R. * Except mammalian RBC all living cells have ribosomes. (Both prokaryotes & Eukaryotes) 80s = 60s + 40s 70s = 50s + 30s * Ribosomes are smallest cell organelles (150 x * At the time of protein synthesis, several ribosomes become attached to m-RNA with the help of smaller 250 A 0 ) Ribosomes are organelle without subunits. This structure is called polyribosome or membranes. polysome or Ergosome. * Ribosomes are also called as ‘‘Organelle with in an organelle’’ & "Protein factory of cell". * S= Svedberg unit or Sedimentation rate 14 Cell : The Unit of Life After synthesis on ribosomes, protein are transported in cytoplasm and organelles. The proper folding and transport of proteins is assisted by specific proteins called Chape ro ns . MICRO–BODIES : * NUCLEUS : The cells of protozoa, fungi, plants, liver and Introduction : kidney cells contain certain membrane bounded * Detail studied in orchid root cells and named by spherical bodies of 0.3 to 1.5  diameter, filled with Robert Brown in 1831. Credit of discovery goes to enzymes are called as ‘‘Micro–Bodies’’. Robert Brown. MICROTUBULES * * Microtubules are composed of contractile protein, Tubulin. * In plants microtubules often found associated with cell wall. Probably these transport cell wall material * from Golgi body to outside of cell. During cell division these microtubules form spindle fibers. * MICROFILAMENTS Microfilaments are long rods 40-50A0 in thickness and distributed throughout the cytoplasm. They are composed of contractile protein, Actin which concern with muscle contraction, and cyclosis. * Microtubules and microfilament provides cytoskeleton-base of cell. "Nucleus is double membrane bound dense protoplasmic body, which controls all cellular metabolism and encloses the genetic information of cell". Nucleus is consider as controller or director of cell. Importance of nucleus in control of heredity. Generally eukaryotic cell contain at least one nucleus but nucleus is absents in mature phloem sieve tube elements and mature RBCs of mammals. (exceptionaly nucleus of RBCs of camel & lamma remains for longer time and degenerates later on) Dikaryotic (Paramecium) and multikaryotic cells are also known. 15 Structure of Nucleus : (i) Nuclear membrane or nuclear envelope or karyotheca. (ii) Nucleoplasm/Karyoplasm/Karyolymph. (iii) Chromatin net (iv) Nucleolus/little nucleus/Ribosome factory (i) Nuclear membrane :- Nucleus is surrounded by two unit membranes, thus nucleus is double membranous component of cell. Space (150 to 300 Å) between two membranes is known as perinuclear space. Outer membrane, of nucleus may connected with E.R. at several places and ribosome also may found on it. * Nuclear membrane is perforated by minute nuclear pores of size, 300 to 1000Å diameter. (ii) Nucleoplasm or Karyolymph :- (Term by Strasburger 1882) Nucleoplasm or Nuclear sap is a ground substance of nucleus which is a complex colloidal formed of a number of chemicals like nucleotides, nucleosides, ATPs, proteins & enzymes of RNA & DNA polymerases, endonucleases, minerals, (Ca++, Mg++) etc. * Nucleoplasm also have enzymes for glycolysis, thus nucleus may obtain energy by glycolysis. * Chromatin net and nucleolus are embeded in nucleoplasm. Nucleoplasm provides site for process of transcription. Cell : The Unit of Life (iii) Chromatin net :- (Term given by Flemming) * It is an intranuclear, (stained with basic dyes) long, thread like fine fibres, which embeded in nucleoplasm. Chromatin net is mainly formed of DNA and histone protein complexes. Chromatin fibres contain genetic information and condensed to form constant number of chromosomes during cell division. * Chemically chromatin consists of DNA (31%), RNA (2-5%), Histone protein (36%) and non histone(28%). 20 to 30% part of histone is made up of arginine and lysine amino acids. * Chromatin net has two type of chromatins (by Emil Heitz). (a) Euchromatin :- This is lightly stained and diffused part of chromatin. Which is transcriptionally or genetically more active. Generally euchromatin lies at central part of nucleus. (b) Heterochromatin :- This is dark stained, thick and condensed part of chromatin this part have more histone and less acidic protein. Heterochromatin is genetically less active chromatin and forms stop point in transcription. Heterochromatin occurs near nuclear membrane. (iv) Nucleolus :- Discovered by Fontana and Term by Bowman. * Nucleolus is naked or membraneless, rounded or slightlyirregularstructurepresentin nucleus and usually attached to chromatin (or chromosomes) of specific site called Nucleolar organiser region/NOR. * Chemistry of nucleolus :Proteins 85% RNA 10% DNA 5% FUNCTIONS OF NUCLEOLUS : Ribosome formation is the chief role of nucleolus, thus its called as Ribosme factory of cell, the proteins of ribosomes are synthesised in cytoplasm but it diffused in to nucleus and reach at nucleolus. Here r-RNA and ribosomal proteins are assembled to form ribosomes which move to cytoplasm through nuclear pores. 16 FUNCTIONS OF NUCLEUS : * (i) Genetic information :- Nucleus contains genetic information in its chromatin. (store house of genetic material) (ii) Transmission of genetic information :- Nucleus takes part in transmission of genetical information from parent cell to daughter cell or the one generation to next. * (iii) In cell-division :- Division of nucleus is pre-requisite to cell division. (iv) Control of metabolism :- Nucleus controls metabolism of cell by sending m-RNA in cytosol (Basically biomolecule DNA controls cellular activities through directing synthsis of enzyme). * Cell : The Unit of Life Chromosomes can be best studied at metaphase stage because size of chromosomes is the shortest during metaphase due to highly condensation of chromatin threads by gelation, dehydration and coiling. (Shape of chromosome (V.L.J.I.) is studied at Anaphase stage) Generally chromosomes in plants are larger than chromosomes of animals, but number of chromosome is high in animals as compared to plants. The number of chromosomes has no relation with any specific feature like size, complexity of organism. (v) Variations :- Variation develops due to change in Chromosome number in some organisms : genetic material of nucleus. (Evolutionary role). CHROMOSOMES : * At the time of cell division the chromatin material get condensed to form chromosomes, thus chromosome is highly condensed form of the chromatin. Chromosomes are not visible during interphase stage. * First of all, chromosomes was observed by Hofmeister (1818) and Karl Nageli in pollen mother cells (PMC) of Tradescantia. * Strasburger (1875) described chromosome structure appeared in nucleus during cell division. (Credit of discovery of chromosomes goes to Strasburger) * Term "Chromosome" was proposed by Waldeyer in 1889. (Term 'Chromatin, was suggested by Flemming) * Generally chromosomes are rod-shaped, * elongated or dot like in shape with size of 0.5 to 32 (Trillium plant has longest chromosome) * 2n = number of chromosome in diploid cell. n = number of chromosome in haploid cell. The number of chromosome is definate for each species. For example every normal human being has 46 chromosomes in each body cell. 17 Cell : The Unit of Life * * Gametes of all organisms contain only one of NEW TECHNIQUES FOR each chromosome. The number of chromosomes IDIOGRAM PREPARATION in a gamete is called "Genome" or haploid Modern techniques used in karyotype chromosome. (Human 23) ‘‘A complete set (n) preparation are ISH, FISH (Fluorescence in of chromosomes (all genes) inherited as a unit Situ Hybridisation), Mc FISH (Multicolour from one parent is known as genome,,. fluorescence in situ Hybridisation) and flow cytometry. Karyotype  Karyotype is external morphology of all Chromosomes of a cell which is specific * for each species of living organisms. Karyotype can be studied in metaphase of mitosis. * (i) (ii) (iii) (iv) Idiogram :– Diagrammatic representation of Karyotype. In idiogram chromosomes are arranged in decreasing order of size. Sex chromosomes are placed in last but in idiogram of Drosophila sex chromosomes are placed first. Idiogram is specific for every species. Karyotype includes the number of chromosomes, relative size, position of centromere, length of the arms, secondary constrictions and banding patterns. Banding technique is used to study USE OF KARYOTYPING OR IDIOGRAM of the specific pattern of bands and interbands (i) It suggests primitive or advanced features of an on chromosome. This includes the use of organism. If karyotype shows a large size fluorochromes (fluorescent dyes). difference between the smallest and the largest chromosome of the set and having fewer Q–banding : It is obtained when chromosomes metacentric chromosomes then it is called are stained with quinacrine mustard. It stains asymmetric karyotype, which is a relatively A–T rich areas (developed by casperson for Y advance feature. Symmetric karyotype is chromosomes). primitive feature. G–banding : Chromosomes are stained with (ii) The karyotype of different species are compared Giemsa. It stains sulphur rich protein parts. and similarities in them represent the evolutionary A variety of different bands are obtained by the relationships. modification of Q–banding and G–banding like (iii) Karyotype is helpful in detection of chromosomal C, T and N–bands. Q, C, G and R banding abberrations and polyploidy. used for animal karyotypes while C and N (iv) In research of medical genetics Forensic banding used in plants. science cytogenetics and Anthropogenetics. C-banding :- It is used to stain constitutive 1. heterochromatin , usually in centromeric region of the chromosome. The process involves denaturation of chromosome by heat or trisodium 2. citrate and then apply giemsa stain. R-banding :- The process involved incubation of the chromosomes in a buffer at high temperature followed by use of Giemsa stain. This brings about 3. the visualization of sulphur deficient region of chromosomes thus named as reverse giemsa. In Situ Hybridization : Using DNA probe labelled with radioactive molecule to locate the position of DNA sequence on chromosome. Fluorescence in Situ Hybridization (FISH) : DNA may also be labelled with fluorochrome to locate the position of DNA sequence on chromosome. Multicolour Fluorescence in Situ Hybridization (Mc FISH) : More fluorochrome colour to locate the position of DNA sequence on chromosome. 18 4. * Flow cytometry : This is recent technique. In * this technique a suspension of many thousands of chromosome is made and the suspended * chromosome are stained with a DNA binding flurochrome. These chromosome pass through the cytometer 4. the fluorescence is measured for individual * chromosome and the result is represented in the form of histogram. * Each peak in this histogram represent, chromosome or a group of chromosome of same size. * This technique allow detection of difference as small as 1.5 to 4.0 Mega base pair. * This technique allow detection of aneuploidy/ duplication or deletion. * STRUCTURE OF CHROMOSOME Pellicle – This is outermost, thin proteinaceous covering or sheath of chromosome. 2. Matrix – This is aliquid nongeneticachromatic ground substance of chromosome, which has different type of enzymes, minerals, water, proteins. 3. Chromonema (singular Chromonemata) Term by Vejdovsky. Sometimes bead like structure are seen on chromonema fibres, which are called as chromomeres. Centromere/Kinetochore :- (Primary constriction) Each chromosome (at metaphase) is consist of two half chromosome or two chromatids. Both the chromatids of a chromosome are joined or connected by a structure called Centromere. At this point or centromere two protein discs are present which is called Kinetochore. Kinetochores constitute the actual site of attachement of spindles to chromosomes during cell division. Centromeric DNA is called as alphoid DNA. * At the region of centromere the chromosome is comparatively narrower than remaining part of chromosome, thus it is termed as Primary constriction. 5. Chromatid – At metaphase stage each chromosome is consist of two cylindrical structures - called chromatids. Both sister chromatids or longitudinal half chromosome are joined together by a common centromere. A chromosome, may have single chromatid (in Anaphase or Telophase) or two chromatid. (as in metaphase) (Parts which appears in metaphase chromosome) 1. Cell : The Unit of Life Each chromonemata is consist of a single long thread of DNA associated with histone.  This is an important, genetical, highly coiled thread, throughout the length of a chromosome or chromatid. 6. It was called chromonema. Chromonema lie embeded in matrix. Secondary constriction : Besides primary constrictions one or two, other constriction may also occurs on some chromosome, which are known as secondary constriction. * Secondary constriction is also known as NOR (Nucleolar organizer region)(13,14,15,21,22 chromosomes in human) 7. Satellite : part of chromosome remains after the NOR is known as chromosomes satellite/ Trabent. * Chromosomes with satellite part are called as SAT chromosome (SAT = SineAcid Thymonucleinico) 19 Cell : The Unit of Life TYPES OF CHROMOSOMES ON THE BASIS OF POSITION OF CENTROMERE : (iv) Sub metacentric :- When the centromere located near centre or mid point of chromosome. * (i) Telocentric :- When centromere is terminal or located at the tip of chromosome. The ratio of length of the long arm to the short arm of a chromosome is called arm ratio. Arm ratio is maximum in acrocenteric chromosome. (ii) Acrocentric :- When the centromere is subterminal or located near the tip. (iii) Metacentric :- When the centromere is located at mid of the chromosome. 20