NEET II AIIMS [UNIT OF LIFE ] ILLUSTRATED 1 UNIT III CELL : STRUCTURE AND FUNCTIONS 123-172 Chapter 8 : Cell : The Unit of Life Topic: • 8.1 What is a Cell? • Cell is the fundamental structural and functional unit of all living organisms. • Anything less than a complete structure of a cell does not ensure independent living. Like – virus • Anton Von Leeuwenhoek first saw and described a live cell. • The cell was first discovered and named by Robert Hooke in 1665. [ It looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name] • Micrographia – book written by Robert Hooke • Robert Brown discovered the nucleus. • C. Benda discovers mitochondria • G.N. RAMACHANDRAN discover of the triple helical structure of collagen • 8.2 Cell Theory o Proposer- . Matthias Schleiden, a German Botanist . Theodore Schwann, a British Zoologist . Rudolf Virchow [modifier] o Theory – . all living organisms are composed of cells and products of cells. All individual cell can perform its activity alone but they doesn’t do so, rather acts as a tissue or organ . all cells arise from pre-existing cells. o Indirect meaning – . Cell is a structural & functional unit of organism • 8.3 An Overview of Cell o Mycoplasmas, the smallest cells [0.3 μm] o Other common bacteria [3 to 5 μm] o largest isolated single cell is the egg of an ostrich o human red blood cells are about 7.0 μm in diameter o Nerve cells are some of the longest cells • Concept of o Protoplasm – organized living part of the cell surrounded by the cell membrane • Protoplasm = Animal cell – [Cell membrane + non living substance (Metaplastic body / argastic substance] o Protoplast – Organized part of the cell excluding cell wall. Protoplast = Protoplasm + [Cell membrane + non living substance] . Protoplast = whole animal cell . Protoplast = Plant cell / bacterial cell – cell wall o Cytoplasm – Organized living part of protoplasm excluding the nucleus . Cytoplasm = Cytosol [Gel like substance] + Cell organelle o Cell organnele – . Amembranous - 1. Ribosome 2. Centrosome 3. Informosome 4. Polysome / Polyribosome . Membrane bound - • Single membrane – 1. ER Medonix Education Service, Foundation II Medical(NEET) II Engineering(JEE-Main; WBJEE) 1 2/129/2 Jatin Das Nagar; Belghoria; Kol—56 M: 8697824633; L: (033)2541-1493; 6674; medonixeducation.in; [email protected] NEET II AIIMS [UNIT OF LIFE ] ILLUSTRATED 2 2. Golgi body 3. Lysosome 4. Vaccuole 5. Spherosome 6. Glyoxysome 7. Peroxysome • Double membrane – 1. Nucleus 2. Mitochondria 3. Plastid • 8.4 Prokaryotic Cells o Example – . Bacteria . blue-green algae . mycoplasma . PPLO (Pleuro Pneumonia Like Organisms) o Prokaryotic cell structure / bacterial cell structure . Cell wall – • Different structure is seen in different bacteria. Like Gram +ve & Gram –ve bacteria • Cell wall is mainly composed by Peptidoglycan, a heteropolysaccharide o Each Peptidoglycan is chain like structure. o Peptidoglycan is composed by . N-Acetyl glucosamine [NAG] & . N-Acetyl murramic acid [NAM] . Linked by beta 1,4 glycosidic bond o Each Peptidoglycan chain is linked by glycin pentapeptide • Teichoic acids are located in between the peptidoglycan chain . Glycocalyx / Cell coat – outermost layer surrounds cell wall • Slime layer – when loosely bounded with the cell wall • Capsule - when tightly bounded with the cell wall o Ex- polysaccharide capsule -- Pneomococcus Polypeptide capsule -- Bacillus anthracsis o Concept of cell wall deficient bacteria / L form bacteria – . Cell wall deficient bacteria . Can be occurred in – in presence of antibiotic, . Example – Mycoplasma pneumoniae . Cell membrane – similar with eukaryotic cell membrane o Chromosomal genetic material . Other name – bacterial chromosome, Genophore, Nucleoid . Double stranded closed circular DNA . Carries genetic characteristics[somatic] of bacteria . Plasmid: • Extrachromosomal genetic material • Double stranded closed circular DNA • Not obligatory for their survival • Confers survival advantage • Carries antibiotic resistant gene • Example – E.coli consists of pBR 322 • Significance & use: o Carries antibiotic resistant gene o Used in recombinant DNA technology Medonix Education Service, Foundation II Medical(NEET) II Engineering(JEE-Main; WBJEE) 2 2/129/2 Jatin Das Nagar; Belghoria; Kol—56 M: 8697824633; L: (033)2541-1493; 6674; medonixeducation.in; [email protected] NEET II AIIMS [UNIT OF LIFE ] ILLUSTRATED 3 . Cell organelle – consists only amembranous organelle • Except chromatophore & mesosome • Mesosome • Formed by the extensions of plasma membrane • Shape - vesicles, tubules and lamellae • Function – 1. cell wall formation 2. DNA replication and distribution to daughter cells 3. help in respiration 4. secretion processes 5. increase the surface area of the plasma membrane and enzymatic content • Chromatophore o membranous organelle o contain pigments o helps in bacterial photosynthesis • Flagella o three parts – . filament . hook . basal body o Function – motility • Pilli - elongated tubular structures made of a special protein o Function - . Help attach the bacteria to the surface . Sexual reproduction • Fimbriae - small bristle like fibres sprouting out of the cell • Inclusion bodies: o Amembranous structure o Cytoplasmic structure o Stored reserve material in prokaryotic cells o Example – . Phosphate granules . cyanophycean granules . glycogen granules • Gas vacuoles o blue green and purple and green photosynthetic bacteria • Difference between eukaryotic cell & prokaryotic cell o Nucleus o Nuclear protein type [histone/ non histone] o Cell wall o Cell organelle [membranous / amembranous] o Ribosome o Cell division Medonix Education Service, Foundation II Medical(NEET) II Engineering(JEE-Main; WBJEE) 3 2/129/2 Jatin Das Nagar; Belghoria; Kol—56 M: 8697824633; L: (033)2541-1493; 6674; medonixeducation.in; [email protected] NEET II AIIMS [UNIT OF LIFE ] ILLUSTRATED 4 • 8.5 Eukaryotic Cells • Cell membrane o Structure Ultra microscopic structure of Cell membrane Cell membrane is a thin, elastic, selectively permeable, living structure which covers protoplasm of any living cell. There are several postulations about the structure of cell membrane but latest & most acceptable model is proposed by scientist Singer & Nicolson (1972) which is known as “Fluid Mosaic Model”. According to this model --- • Cell membrane is 74 Ao thick bilayer structure. • It is composed by – lipid, protein & carbohydrate. o Lipid : . Each layer of cell membrane is made of by phospholipid. Important phospholipids of cell membrane are – phosphatidyl cholin (lecithin ) & phosphatidyl ethanolamine (cephalin ). Phospholipids are structurally look like a clothe pin which has two end – • head end or polar end or hydrophilic end • tail end or nonpolar end or hydrophobic end. Polar ends are faced towards the Extra Cellular Fluid (ECF) & Intra Cellular Fluid (ICF) . Where as nonpolar ends faced towards at the junction of the bilayer. Some cholesterol present in the phospholipid layer diffusely. o Protein : . Proteins are embedded diffusely within the phospholipid bilayer. This membrane protein can be classified in such way, as --- • According to spatial arrangement, o Peripheral protein or extrinsic protein (present peripherally surface of the membrane). o Integral protein or intrinsic protein (present interiorly) o Transmembrane protein (traversed through & through the cell membrane) • According to function, o Channel protein (helps in ion transport) o Receptor protein (Like receptor of hormone) o Carrier protein (helps in ion transport) o Pump protein (helps in active diffusion) etc. o As protein molecules are arranged diffusely within the phospholipid fluid layer like mosaic particle, so it’s called as Fluid Mosaic Model. o Carbohydrate : . Carbohydrates present in the cell membrane of few animal cell, are in the form of glycolipid & glycoprotein . Which is otherwise named as Cell coat. It renders antigenic characteristics of the cell. Like A, B, O antigen of RBC o Usually percentage of protein, lipid, carbohydrate according to molecular wt. is – 52%, 40%, 8%. Medonix Education Service, Foundation II Medical(NEET) II Engineering(JEE-Main; WBJEE) 4 2/129/2 Jatin Das Nagar; Belghoria; Kol—56 M: 8697824633; L: (033)2541-1493; 6674; medonixeducation.in; [email protected] NEET II AIIMS [UNIT OF LIFE ] ILLUSTRATED 5 • Function of cell membrane: 1. Helps in transport of different solute [most important function] 2. Acts as a osmotic barrier between ECF & ICF 3. Acts as a selectively permeable membrane 4. formation of intercellular junctions 5. helps in secretion 6. Helps in phagocytosis & pinocytosis 7. Helps in formation of ER 8. Helps in formation of pseudopod • Factors depends fluidity of cell membrane: o Cholesterol is the key regulator of membrane fluidity o Cholesterol modifies membrane fluidity o Presence of unsaturated fatty acids in membrane phospholipid increases fluidity o Presence of saturated fatty acids in membrane phospholipid decreases fluidity o Temperature increases membrane fluidity Medonix Education Service, Foundation II Medical(NEET) II Engineering(JEE-Main; WBJEE) 5 2/129/2 Jatin Das Nagar; Belghoria; Kol—56 M: 8697824633; L: (033)2541-1493; 6674; medonixeducation.in; [email protected] NEET II AIIMS [UNIT OF LIFE ] ILLUSTRATED 6 • Transverse diffusion or flip-flop movement of membrane lipid or protein: o movement of membrane lipid or protein from one membrane surface to the other surface o transverse diffusion is a fairly slow process o Most large proteins