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1 POINTS TO REMEMBER : 8. Cell: The Unit f Life CELL THEORY : Schieiden and Schwann tgether frmulated the cell thery. They prpsed that the bdy f animal and plant are cmpsed f cells and prduct f cells. Rudlf Virchw (1855) he mdified and gives the final shape t thecell thery. All living rganisms are cmpsed f cells and prducts f cells. All cells arise frm pre-existing cells. PROKARYOTIC CELLS : Represented by bacteria, blue-green algae, mycplasma and PPLO. Smaller and multiply mre rapidly than eukarytic cells. Fur basic shape f bacteria are Bacillus (rd like) Cccus (spherical) Vibri (cmma shaped) Sprillum (spiral) All prkarytes have a cell wall surrunds the plasma membrane. There is n well defined nucleus. Chrmsme is single and circular, nt envelped by nuclear membrane. Presence f many small, circular, extra chrmsmal and self replicable DNA called plasmid. Plasmid prvides unique characteristic t the bacteria. One f the characteristic is antibitic resistant. N membrane bund cell rganelles. A specialized differentiated frm f cell membrane called messme is present. Cell envelpe and its Mdificatins : Mst prkarytic cell have characteristic cmplex cell envelpe. The cell envelps cnsists f tightly bund three layer structure; The utermst glyccalyx. Middle cell wall Inner plasma membrane. Accrding t the nature f the cell wall and behavir twards the stain develped by Gram, bacteria are Gram psitiver Gram negative. Glyccalyx may fr a lse sheath called slime layer. Glyccalyx may be thick and tugh called the capsule. The cell wall determines the shape f the cell, strng structural supprt t prevent the bacterium frm bursting and cllapsing. Plasma membrane is semi-permeable in nature and interacts with utside wrld. A special membranus structure is the messme which is frmed by extensins f plasma membrane int the cell.

2 These extensins are in the frm f vesicles, tubules and lamellae. They help in cell wall frmatin, DNA replicatin and distributin t the daughter cell. They als help in respiratin and secretin. Sme bacteria have filamentus extensins called flagella. Bacterial flagellum has three parts filament, hk and basal bdy. Pili are elngated tubular structures made f a special prtein. Fimbriae are small bristle like fibres spruting ut f the cell. Play rle in adhesin. Ribsme and inclusin bdies : Ribsmes are assciated with the plasma membrane f the cell. Each ribsme (70 S) has tw sub units; smaller (30 S ) and large (50 S). Ribsmes are the site f prtein synthesis. Several ribsmes attached t a single mrna t frm a chain called plyribsme r plysme. Reserve materials are stred in the frm f inclusin bdies. Phsphate granules, cyanphycean granules and glycgen granules are the inclusin bdies. EUKARYOTIC CELL : Eukarytes include all the Prtists, plants, animals and fungi. Extensive cmpartmentalizatin due t membrane bund cell rganelles. Pssess an rganized nucleus with nuclear envelpe. Have a variety f cmplex lcmtry and cytskeletal structure. Genetic materials are rganized int chrmsmes. The plant cell pssess cell walls, plastids and a large central vacule, which are absent in animal cell. Animal cells have centriles which absent in plant cells. Cell membrane : The cell membrane cmpsed f lipids that arranged in bilayer. Lipids are arranged within the membrane with the hydrphilic plar head twards the uter sides and thehydrphbic tails twards the inner part. Nn plar tail f saturated hydrcarbns is prtected frm the aqueus envirnment. The lipid cmpnent f the membrane mainly cnsists f phphglycerides. Cell membrane als pssesses prtein and carbhydrates. Rati f prtein and lipids varies frm cell t cell. Human erythrcyte plasma membrane cntains 52 % prtein and 40 % lipids. Membrane prtein may be integral r peripheral. Peripheral prtein lie n the surface and integral prteins are partially r ttally buried in the membrane. The imprved mdel f the structure f plasma membrane was prpsed by singer and Niclsn (1972) widely accepted as fluid msaic mdel. Accrding t this the quasi fluid nature f lipid enables the lateral mvement f prteins within the verall bilayer. Functin : Passive transprt. Simple diffusin

3 Facilitated diffusin. Active transprt. Phagcytsis Excytsis. Pincytsis. Cell wall : A nn-living rigid structure called cell wall present utside the plasma membrane f plant and fungal cell. Algae have a cell wall made f cellulse, galactans, mannans and minerals like calcium carbnate. Plant cell wall cnsists f cellulse, hemicellulses, pectins and prteins. The cell wall f yung plant is called primary cell wall. On maturity secndary cell wall frmed inner t it. The middle lamella is a layer f calcium pectate which hlds r glues the neighbring cells. The cell wall and middle lamella may traversed by plasmdesmata; the cytplasmic cnnectin between tw adjacent cell. The endmembrane system : Endplasmic reticulum : Netwrk r reticulum f tiny tubular structures scattered in the cytplasm, called endplasmic reticulum. It divides the intracellular space int tw distinct cmpartments: Luminal (inside the ER) Extra luminal (cytplasm). The ER shws ribsmes attached t their uter surface called Rugh Endplasmic reticulum (RER). Endplasmic reticulum withut ribsme called SER (smth endplasmic reticulum) Functin: RER present in the cell actively invlved in prtein synthesis. SER is the site fr synthesis f lipid, glycgen and sterid hrmnes. Glgi apparatus: Camill Glgi (1898) first bserved this rganelle, and named after him. It cnsists f many flat, disc shaped sacs r cisternae. These are staked parallel t each ther. The Glgi cisternae are cncentrically arranged near the nucleus with distinct cnvex cisr the frming face and cncave transr the maturing face. Functin: Principally respnsible fr packing f materials t be delivered intra-cellular target r intercellular target.

4 Materials are packed in the frm f vesicles, frm the ER fuse with the cis face f the Glgi apparatus and mve twards the trans face. Imprtant site fr the frmatin f glycprtein and glyclipids. Lyssmes: Membrane bund vesicular structure. Frmed by Glgi bdy. Rich in all type hydrlytic enzymes, ptimally active in acidic ph. These enzymes are capable t digesting carbhydrates, prteins, lipids and nucleic acids. Vacules: The vacule is the membrane-bund space fund in the cytplasm. It cntains water, sap, excretry prduct. Vacule is bunded by a single membrane called tnplast. In plant cells the vacule can ccupy 90% f the vlume. Tnplast facilitates active transprt f material frm cytplasm int the vacule. In Ameba the cntractile vacule is imprtant fr excretin and smregulatin. In many prtists, fd vacules are frmed by engulfing the fd particles. Mitchndria: The number f mitchndria varies accrding t the physilgical activity f the cell. Each mitchndrin is a duble membrane bund structure with uter and inner membrane, dividing its lumen int tw aqueus cmpartments Outer cmpartment. Inner cmpartment. The inner cmpartment is called the matrix. The inner membrane frms a number f infldings called the cristae twards the matrix. The cristae increase the surface area. Tw membranes have their wn specific enzymes assciated with the mitchndrial functin. Mitchndria are the site f aerbic respiratin. They prduce cellular energy in the frm f ATP, hence called pwer huse f the cell. The matrix als pssess single circular DNA mlecule and a few RNA mlecules, ribsmes (70S), they synthesize their wn prtein. Mitchndria divide by fissin. Plastids : Plastids are fund in all plant cells and in Euglenids. They bear sme specific pigment, impart specific clur t the plants. Based n the type f pigments plastids can be classified int Chlrplast. Chrmplast Leucplast.

5 The chlrplasts cntain chlrphyll and cartenid pigments, traps slar energy fr phtsynthesis. In the chrmplasts fat sluble cartenid pigments like cartene, xanthphylls are present. The leucplasts are clurless plastids f varied shapes and size with stred nutrients. Amylplast - stre carbhydrates. Elaiplasts stre ils and fats. Aleurplast stre prteins and minerals. Chlrplasts are fund in the mesphyll cells f the leaves. These are val, spherical, discid r even ribbn like rganelles. Chlrplast is a duble membrane rganelle. The space limited by inner membrane is called strma. A number f rganized flattened membranus sacs called thylakid are present in the strma. Thylakids are arranged like stakes f cins t frm grana. There are flat membranus tubules called the strma lamellae cnnecting the thylakids f the different grana. They thylakids enclse a space called lumen. Chlrphyll pigments are lcated in the thylakids. Chlrplast cntains enzymes required fr the synthesis f carbhydrates and prteins. Strma cntains small circular DNA and ribsmes. Ribsmes : Ribsmes are granular structure first bserved by Gerge Palade (1953). Cmpsed f ribnucleic acid (RNA) and prteins. Nn-membranus cell rganelles. Eukarytic ribsmes are 80S while the prkarytic ribsmes are 70S. S stands fr sedimentatin cefficient; measure f density and size. Bth 70S and 80S ribsmes cnsists f tw subunits. Primary functin is prtein synthesis hence called prtein factry f the cell. Cytskeletn : An elabrate netwrk f filamentus prteinaceus structures present in the cytplasm is cllectively knwn ascytskeletn. Cytskeletn invlved in many functin such as mechanical supprt, mtility, maintenance f the shape f the cell. Cilia and Flagella : Cilia and flagella are hair-like utgrwths f the cell membrane. Cilia are small help in the mvement f cell r surrunding fluid. Flagella are lnger and respnsible fr cell mvement. Cilia and flagella cvered by plasma membrane. Their cre called axneme, pssess a number micrtubules running parallel t the lng axis. The axneme usually has nine pairs f dublets f radially arranged peripheral micrtubules and a pair f centrally lcated micrtubules. The central tubules are cnnected by bridges and are als enclsed by a central sheath, which is cnnected t ne f the tubules f each peripheral dublet by radial spke. The peripheral dublets are als intercnnected by linkers.

6 Bth cilia and flagella emerge frm centriles-like structure called basal bdies. Centrsme and centriles : Centrsme is an rganelle usually cntaining tw cylindrical structures called centriles. They are surrunded by amrphus pericentrilar materials. Bth centriles in a Centrsme lie perpendicular t each ther. Each centrile has an rganizatin like the cartwheel. They are made f nine evenly spaced peripheral fibrils f tubulin. Each f the peripheral fibril is a triplet. The adjacent triplets are als linked t each thers. The central part f the centrile is called hub. The hub cnnected t peripheral triplets by radial spkes. The centrile frms the basal bdy fr cilia, flagella and frm spindle fibres during cell divisin. Nucleus : Nucleus as a cell rganelle was first described by Rbert Brwn in Materials inside the nucleus was stained by Flemming and named as chrmatin. The interphase nucleus has highly extended and elabrates nucleprtein fibres called chrmatin. The nucleus als cntains nuclear matrix and ne r tw spherical bdies called nucleli. Nuclear envelpe cnsists f tw membranes with perinuclear space (10-50 nm). The uter membrane remains cntinuus with endplasmic reticulum. Presence f nuclear pre due t fusin f tw membranes. Nuclear pres allw the mvement f RNA and prtein in bth directins. The nuclear matrix r nucleplasm cntains nuclelus and chrmatin. Nuclelus is the site fr active ribsmal RNA synthesis. During cell divisin the chrmatins cndensed t frm chrmsmes. Chrmatin cntains DNA and sme basic prteins called histnes, nn-histne prteins and sme RNA. A single human cell cntains apprximately tw meter lng thread f DNA in 46 chrmsmes. Each chrmsme essentially has a primary cnstrictin r the centrmere. On each side f centrmere there is disc shaped structures called kinetchres. Based n the psitin f the centrmere chrmsmes are classified int fur types:- Metacentric: centrmere at the middle with tw equal arms. Sub-Metacentric: ne shrt arm and ne lng arm. Acrcentric: with extremely shrt arm and a very lng arm. Telcentric: with terminal centrmere. A few chrmsmes have nn-staining cnstrictins at a cnstant lcatin. This gives the appearance f a small fragment called the satellite.