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Cell: The Unit of Life * Cell: Fundamental, Structural and functional unit of living. Z g Thin membrane (PM), Cell wall apache to 7 ania and roineae organisms are composed of cells and products of cells. Rudolf Virchow (1855) : Omnis cellula-e cellula Organisation of the prokaryotic cell is fundamentally similar even though prokaryotes exhibit a wide variety of shapes and functions. Mycoplasma (smallest cell) 0.3 pm (length) PPLO 0.41pm Bacteria 3-5 pm (length) 1-2 pm RBC 7ym Typical Eukaryotic cell 10-20 ym Typical plant cell 50 pm Viruses 0.02 - 0.2 pm * Cell Envelope of Prokaryotic cell © Cell Wall = Flagella (filament, hook, basal body)(motility) = Mycoplasma lacks a cell wall. e Cell Membrane : = Consists of mesosomes, special membranous structure formed by inward extension of cell membrane (in form of vesicles, lamellae and tubules), help in: ® Cell wall formation * DNA replication and distribution * Respiration « Secretion * Increase surface area of plasma membrane and enzymatic content = Cyanobacteria consists of chromatophore, (membranous extensions) which contain pigments = Surface structures(arise from cell wall) : Flagella, pili and fimbriae for attachment. « Ribosomes Observed as a dense particle by George Palade (1953) . All living cells have ribosomes except RBC. 80s (60s + 40s) : Eukaryotic cell and RER. 70s (50s+30s) : Prokaryolic cell, MT and Chloroplasts. § = Svedbergs unit or sedimentation rate ( density and size) Mg" essential for bonding two subunits Several 70s ribosomes attach to single MRNA to form polysome/polyribosome (translation) 15nm - 20nm . Inclusion bodies (non membrane bound): Store reserve material in prokaryotes. Ex. phosphate granules, cyanophycean granules and glycogen granules. * Gas vacuoles (membrane bound) in blue, green . purple and green photosynthetic bacteria. * Cell Membrane (eukaryotic) a o o a a a The major lipids are phospholipids that are arranged in a bilayer Non polar hydrophobic tail of saturated hydrocarbon Erythrocyte : 52% Protein, 40% Lipid, 8% Carbohydrates Fluid mosaic model : Singer and Nicolson (1972) The quasi fluid nature of lipids enables lateral movement. Fluid nature accounts for cell growth, formation of intercellular junctions, secretion, endocytosis, cell division etc. Cholesterol causes rigidity. It is absent in prokaryotes. ® Cell Wall Absent in mycoplasma Helps in cell to cell interaction Algal cell wall: Cellulose. Galactans, mannans, CaCQ,. Plant cell wall : Cellulose, hemicellulose, pectins and proteins Middle Lamella consists of Ca pectate and Mg pectate. (Ca>Mg) Cell wall material composed by golgi bodies or dictyosomes and secreted by plasma membrane. Plasmodesmata is present in plants only. * Cytoplasm : Semifluid matrix On PM Arise from basal bodies Posses microtubules Their core, called the axoneme, possesses a number of microtubules running parallel to the long axis. The axoneme usually has nine doublets of radially arranged peripheral microtubules, and a pair of centrally located microtubules o Radial spikes : b/w central sheath and peripheral microtubules © Interdoubletbridges : b/w two doublets © Linkers : b/w microtubules of a doublet * Centrioles (9 Triplets + 0) o Centrosome — 2 centrioles at 90 degree o Centriole : Exclusive to animal cells. Perform cell division. © Surrounded by amorphous pericentriolar materials e000 e Non membrane bound © Microtubule fibrils o Radial spokes : bfw hub and peripheral triplets © A-C linker : b/w two peripheral triplets ® Nucleus 2 Described by Robert Brown (1831) © Chromatin by Fleming. © 10-50ym Perinuclear space © Nucleolus : rRNA synthesis Short arm: p eo Longarm:q « Microbodies present in both plant and animal cells A ype exkaryoce ext 110-20 ae Tigers 03 BP Ribosome © Chiasmata disappear © Nucleus and organelles dissolved © Meiotic apparatus assembled * chromatid 1 kinetochore ® Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms, even though the process, per se, paradoxically, results in reduction of chramosome number by half. 
