Ultrastructure of Cells and Organelles PDF

Study of Ultra Structure of Prokaryotic and Eukaryotic Cell through Electron... 11 3. Inner to the cell wall is...

Study of Ultra Structure of Prokaryotic and Eukaryotic Cell through Electron... 11 3. Inner to the cell wall is the plasma membrane which functions as a selective Stud! of Ultra Structure of barrier and allows sufficient passage of nutrients, oxygen and wastes. Experiment prokaryot,c and Eukaryotic Cell 4. Surface of most bacterial cells are surrounded by fimbrae/pilli which are made of sub units of proteins called pi line. These are hollow, non-helical, through Electron Micrograph: 3 and Photographs short, rigid projections from the wall which are more numerous than flagella. Pilli has two main functions (i) help the bacteria to attach firmly to any smooth surface and prevent the bacteria from being washed away (Fig 3.2A). (ii) F-pilus plays an important role in bacterial conjugation. 5. Most bacteria posses flagella for motility. These are hair like helical l and functional units of life. Several features are com appendage that protrude through the cell wall, are many times longer than Cells are the struc turacells are surrounded by plasma membrane (ii) Piamon.) All.. sma the cell and are responsible for swimming motility (Fig 3.2A). Flagella are all cells. (1 10 ells enclose a viscous fluid cal 1ed cytosol/cytoplasm (iii) All of simple type, thinner than eukaryotes only 0.0 I-0.02µm thick and do not f 3 II c membrane.O hromosomes genes ma de of DNA(.iv) All cells contain tin with Y show 9+2 microtubular arrangement. cells contmn c.... d f roteins and RNA called ribosomes. which synthesise proteins 6. Inner to the membrane lies the cytoplasm which contain different types units ma e o P.. as per the instruction of the gen~s (:) All cells multiply and d1v1de by duplicating of bio-molecules including enzymes for various metabolic activities. DNA which is equally distributed to the two newly fon11ed daughter cells. ribosomes, that are essential for protein synthesis and varied types of their. I d"ffi I. I.. There are two basic types of cell~_wh1c 1 1 ~r great y m t 1e1r mternal structure storage granules (volutin granules, sulphur granules etc). namely: (i) Prokaryotic cell and (11) Eukaryot1c cell. 7. In the central region of the cytoplasm lies the Nucleoid which appears as an irregular shaped lighter region (Fig.3.2B). Each nucleoid region contains PROKARYOTIC CELL one molecule of long, double stranded circular DNA known as bacterial The wordprokaiyotic is derived from a Greek word pro means "before" and ka1y 011 chromosome. means "kernel" in cell refers to nucleus. In prokaryotes the DNA is concentrated in a region called nucleoid which is not surrounded by a membrane hence the nuclear material lies naked within the cytoplasm. There are no membrane bound \.. - - - Cell Wall organelles present in the prokaryotes. Most of the vital functions are performed by U1e plasma membrane hence prokaryotic cells are primitive type without Mi~- - Plasma membrane any functional compartmentalization. Prokaryotes include Bacteria and Archaea. Smallest cell known as Mycoplasma, have a diameter between 0.1-1 µm. Due to the smaller size the ratio of the surface area to volume is greater in all the Nucleoid cells. Most bacteria are 1-1 0µm in diameter, can be seen as small rods or circles under high power of light microscope and the entire cellular details can be observed through electron micrographs. Bacteria can be non-photosynthetic and photosynthetic. Non-Photosynthetic Prokaryotic Cell: Bacteria- Pseudomonas aeruginosa (Fig 3.1) I. The ~ell is surrounded by a rigid cell wall made up of peptidoglycan, which provides support and shape to the cell. 2- In some cells the ce II wa II 1s · enclosed with a mucilaginous cover calle d Thin Section Transmission Electron Microscopic (TEM) Fig. 3.1 the capsule. which protects the cells from dehydration and make it. anti. View of Pseudomonas aeruginasa Phagocytot 1c henc e, eva des tie 1.immune system of the host.  ual of Cell Biology Study of Ultra Structure of Prokaryotic and Eukaryotic Cell through Electron... 13 Man.. 12 Laboratory small ext ra : hromosomc, bactena often contain are called photosynthetic lamellae, which.. 10 the bacte11a 1 c. 6_ The infolded membranes g In add111on. d bl stranded DNA called plasmids (eg. F-Particl e.) contain pigments and enzymes involved in the light capturing process of · ecircular ou e.. chro1110s0 1n.. waoinated al certain portions to further increas e photosynthesis. 1nembranc 1s II e 9_ The plasma ,foldings are known as mesosomes (Fig 3.28) 7. The concentric membranes are lined on both surfaces with granular ~ area and I1iese II the sur ace' , ,stem and the membrane bound organelles like phycobilisomes which store the accessory pigments. don1e111brnne S) 10. The en Goloi bodies etc are totally absent. mitochondria. lysosome. e.- ·' · Flagellum ~ ~ - - - - - - - - - -- - Cytoplasm ,lus Cytoplasm _ _ _ _ _ __ Cell wall Ribosome ~\rt/ ~ --. c1 0 ~ Cel1Wall Cytoplasmic Membrane ~ - - ~ Capsule ·- ,----1+-- - Mesosome ~ - - -- - Pholosynthclic ¾;I ~\K. lamcllae /1... CellWall t 0'-·-_.'°-+'-- - Nuclear Malerial Nucleoid I D~~r,L.-== - Phycobitisomes (A) (B) Fig. 3.2 Labelled Diagram of Non Photosynthetic Bacterial Cell : A. Surface Detail B. Sectional View Photosynthetic Prokaryotic Cell: Blue Green Algae-Synechococcus lividus (Fig 3.3) Fig. 3.3 E.M. of Thermophillic Blue Green Algae- Synechococcus lividus I. The basic features, described above are common to_the photosynthetic Showing Concentrically Arranged Photosynthetic Lamellae and bacteria also. Phycobilisomes Attached to them 2. The plasma membrane inner to the cell wall , enclosing the cytoplasm and nucleoid perfonn the function of photosynthesis. 3. The plasma membrane infolds at some sites and these folding extend into EUKARYOTIC CELL the cytoplasm as concenLric foldings called the thylakoid. Eukaryotic cells are more complex and are bigger than prokaryotic cells. Eukayotic 4- The thylakoids are distributed as single element extended from the plasma cells are typically I0-100 µm in diameter, can be easily observed even under the membrane in the cytoplasm and not enclosed in organelle (chloropla st ) as low power of the light microscope. All eukaryotic cells (Greek eu means ·'true" in eukaryotes. and karyon means "nucleus") have true nucleus in which the nuclear material 5· The chlorophyll pigments are embedded in the concentri c thylakoid is enclosed within the membranous nuclear envelop and is separated from the membrane. cytoplasm. Unlike the prokaryotes, there are various membrane bound organelles which carry out different functions hence functional comparonentalization exi sts. I j  -- Electron... 15 The book h I of Cell Biology.. Study of Ultra Structure of Prokaryotic and Eukaryotic Cell through the latest L boratory Manua 14 a branc system present within each eukaryotic , which System (C. a well orga111se. d endomem 3. Plasma membrane encloses the viscous fluid called the cytoplasm (") A · I with the comprehens There 1s s· (i) Plant cell and II. bmma cell. Although contains various membrane bound organelles. The cytoplasm along practical as th ty I eel.. II are of two type.. pes, there are plasma membrane is called the protoplasm. Students as Eukaryouc ce s I. functions remam same m o of the cell, which ents and t ,eir. 4. The nucleus is one of the most important organelle difficult to the basic compon. both types of cells. wall (ii) contains the major genetic information of the cell. sessions. Th certain unique features i; lant cells absent in animal cells (1) Cell follow lon g Unique features PV: O le with tonoplast (iv) Plasmodesmata. s. Nucleus is separated by a double membrane envelop from the surrounding f nuclear been elab "') Central acuo cytoplasm and usually occupies the central region of the cell. The \.. Chloroplast (111 imal cells which are absent rom Plant cells: (i) matrix througho ut its ~ comprehen s d with pores and contain nuclear f Unique features '" An "th Centrioles (iii) Flagella/Cilia (present in envelop is perforate called the (") Ccntrosome w, interior. Within the nucleus DNA is organised into discrete units We/1-labell e Lysosomcs n f plant sperm cells). t is the lower groups o.. chromosomes. A prominent structure within the non dividing nucleus of actual ex some. 4 is bounded by a rigid cellulos1c cell _wall which fonns nucleolus where the ribosoma l RNA synthesis takes place. which will 3 besides I. Plant cell (Fig. · ) CeII wall gives the plant cell defimte shapes 6. The endoplasmic reticulum (ER) is an extensive network of membranous 'if the experim h terrnost layer. has numerous pores or gaps called called the It the experim t e ou· a protective. 1ayer· The cell wall system made up of inter connected tubules and flattened sacs ~ and readin forrnmg through which the protoplast is interconnected in multi cisternae and is continuou s with the nuclear envelop. In plant cells it forms the plasmodesmata help the le a ellular organisms.. a continuous channel to the adjacent cell through the plasmodesmata. have also b c b ane which is the outer most 1ayer m ammal cell, lies 7. The ER cisternae can be smooth or are studded with ribosome s on its p answers of 2 The plasma mem rII in plant cells. Due to the absence of ce II wall animal the name smooth ER and rough ER respectiv ely. ·.mner to the ce 11 wa. outer surface and hence muscular provided fa cells are devo1 o.d f definite shape and are mostly circular. The smooth ER is primarily associated with lipid synthesis and result of w movement and rough ER for secretary protein synthesis. personally ous sacs- well tested. 8. The Golgi apparatus consists of stacks of flattened membran and each cisternae, with bulging ends. The stacks are not interconnected. This cisternae, in a stack separates its internal space from the cytoplasm of certain organelle is associated with the processing and packaging secretary proteins synthesised by the rough ER. energy 9. All eukaryotic cells have one or more mitochondrion which generate some rich ATP through the process of aerobic respiration. It also contains genes in its circular DNA. chlorophyll I 0. In plants plastids form an important component of the cell. The thesis bearing plastids called chloroplast perform the function of photosyn own DNA and can code for some of their own proteins. and contain their are bound by 11. Vacuoles fom1 an important component of plant cells which are membrane called the tonopl ast and are filled with vacuolar sap. Vacuoles following functions : (a) Tempora rily store substance s known to perform the c wastes like proteins, sugars, organic acids and inorganic ions. (b) Metaboli ic and poisons are also accumulated in the vacuoles to prevent cytoplasm up water to increase the cell size and maintain damage. (c) Vacuoles take rigidity/turgidity of the cells. spaces Price: Rs. Fig. 3.4 Diagrammatic Sketch of a Typical Plant Cell ISBN: 978  Study the Ultra Structural Details of Various Cellular Organelles Using Electron... 17 lam in matrix by lam in-binding proteins present in the chromatin. Chromatin becomes highly condensed during mitosis to form the compact metaphase chromosomes that are distributed to daughter nuclei (Fig. 4.2). Experiment study the Ultra Structural Details of 9. The most prominent nuclear body is the nucleolus, which is the site of various Cellular Organelles Using rRNA transcription and processing of ribosome assembly. The nucleolus 4 Electron and Photo Micrographs thus contains portions of DNA where rRNA genes are clustered to form a structure called the nucleolar organizing region (NOR). Cells typically have one or more nucleoli. Nudut porct Nuc\coul Euchromltin HetaoChromlrin (I) NUCLEUS (11) MITOCHONDRION (111) CHLOROPLAST (IV) ROUGH AND SMOOTH ENDOPLASMIC RETICULUM (V) GOLGI APPARATUS (VI) CYTOSKELETON (VII) MICROBODIES Nucleus (Fig. 4.1 A, B) I. The presence of a nucleus is the principal feature that distinguishes eukaryotic cells from prokaryotic cells. Nucleus serves as a repository of oenetic information controlling essential activities like DNA replication ~ranscription and RNA processing. A ' 2. The nuclear envelope demarcates the nuclear contents from the cytoplasm and also provides the structural framework of the nucleus. It acts as a barrier and prevents the free passage of molecules between the nucleus and the cytoplasm. 3. The nuclear envelope has a complex structure consisting of two membrane bilayers -inner and outer nuclear membranes, an underlying nuclear lamina, and nuclear pore complexes (NPCs). 4. The outer nuclear membrane is continuous with the endoplasmic reticulum, so the space between the inner and outer nuclear membranes is directly connected with the lumen of the endoplasmic reticulum. 5. Underlying the inner nuclear membrane is the nuclear lamina a fibrous meshwork that provides structural support to the nucleus. Tl;e nuclear lamina is composed of 60- to 80 kilodalton (kd) fibrous proteins called l~m111s. Lam111s are a class of intermediate ti lament proteins. 6- 1 he nuclear pore complexes are the only channels through which small polar molecules , io 11s an d mac1omo. 1ecules (protems. and R.NAs) can travel between the nucleus and the cytoplasm. 7- rhe nucleus conta·ins ti1e genetic · matenal..111 the form of a DNA-protein complex...known as th e cI1ro111at111. Almost I0% of the interphase chromat111. is m a t'1H~hly chrom ~. hcondensed. t ca II ed the heterochromatin. Much ol. the sate a 111 111 Ide interphase or ti ie non -d'1v1d111g and distr'b.. stage remains decondense d 1 ute tIiroughout ti. 8. The chromat'.. ic nuc Ieus and 1s· known as euchromat111 ·. Rough ER the chromoso111 111 t11e 111tcrph ase appears to be uni form ly disperse d but B and occupy d'111 es are actuall)'. ·. ' organized discrete functional domains 111to · iscrcte regions of Fig. 4.1 Structure of Nucleus: A. An Electron Micrograph B. Schematic Iarge loops of DNA. ti ie nuc Ieus. Chromatin is organize d into. Representation of its Structural Features · and specific regions· of these loops are bound to tie I  Manual of Cell Biology L.abora tory Study the Ultra Structural Details of Various Cellular Organelles Using Electron... 19 [f:ffYfYJ ] 2 nm The NPC structure consists of a scaffold that anchors the complex w th~ 5. nuclear envelope, a cytopl:umlc and a nuclear ring. a nuclear ballket an DNA double hcli.x eight eytopla.~mic filaments. ] 11 nm Nucleosomcs ("beads on a string") - ] JO run chrom,ti,, fib 1. Aseries Golg1 appar atus and vescicle s ,ronn organe I t 1c en lie such as endoplasmic reticu... domcmbrane system. which 1s 111vol lum,.. ved 111 theffi synthesis Proce ss1ng. la;... \~ t pathway ~ ' f ,,. @ Lysosome Late c Cyro., o/ protei ns. Yes1c 1 es Ira c molec ules (vesicu Secretory ' prwin ® cndosom movement and storage of but also granule ~ r comp artme nts Regulated i:t/JI transport) not only between various intracell~la secrete molecules to the cell surface as well (Fig. 4.7). 2_ Endoplasmic reticulum (ER: s_imply _means_net work wit~in the cytoplasm) secretory pathway f!}).t t._ ~ f connectmg membranous ~ J. J. Golgi complex forms an extensive three-d1mens1onal 111ter network of contin uous vesicl es, tubule s and flatten ed sacs. ER is bound by ~~ trall.f Golgi network es a space know n as cisternal space trun:r Cistcma a single cell membrane, which enclos medial Cistema or lumen. the perinuclear space between ci.r Cistcma 3. The cistemal space of ER is continuous with 4.8 A). the two membranes of the nuclear envelop (Fig. or rough ER (RER Fig. 4.8 B), 4. There are two types of ER: (i) Granular which is studded with riboso mes on its cytoso lic ar surfac type). e. RER is typically The ribosomes are \ I composed of a network of flattened sacs (lamin I:,.:, lic side of the ER memb rane due to the presence of attached to the cytoso are attach ed with the bigger ribosome receptor (ribophorin). Ribosomes mes where the riboph orin recog nition proteins are subunit of the riboso which lacks (SER Fig. 4.8 C), present. (ii) Agranular or smooth ER sed of highly wavy and tubua r memb ranou s structure Nucleus ribosomes. It is compo (tubular type). 5. In a typical mammalian cell 50-90% of the total membrane is devoted to ER Q by the cisternal space. and 10% of the total cellular volume is represented ly involv ed in the biosy nthesi s of secertory proteins, 6. The RER is active ns and the quality control of N-linked glycosylation of the nascent protei by the bound riboso mes. It also helps in the correct the proteins synthesised folding and assembly of multim eric protei ns. esis, drug detoxification, 7. The SER in contrast is involved in lipid synth and regula tion of calcium levels glucogenesis, steroid hormone synthesis in the cytosol (sarcoplasmic reticulum). 8 s of Golgi complex and - The ER can communicate with the inner space means of vesicl mes byres. es (vesic ular transp ort) that shuttle between Fig. 4.7 An Overv iew of the Netwo rk of Organ elles Involved in Secretory lysosostructu these and Endoc ytic Pathways (GERL) 9 · ER, Golgi complex and lysosomes are functionally inter-c onnected hence known as GERL complex (Fig. 4.7). ~ S-- M 26 Laboratory a nu al of Cell Biology - - - -- - -- - - - - - - Study the Ultra Structural Details of Various Cellular Organelles Using Electron... 27 A A ER-Golgi lntennediate Compartment Fig. 4.8 A. Schematic Illustration Depicting the Organization of the ER which is Continuous with the Nuclear Envelope B. EM of Sectional View of Rough ER where Membranes are Studded on their Outer Surface with Ribosomes. C. Smooth ER are Layers of Tubular Membranes and Devoid of Ribosomes Plasma Membrane, Secretion. Endosomes, Lysosomcs B Golgi Complex (Fig. 4.9 A, B) Fig. 4.9 A. Electron Micrograph of Golgi Apparatus. B. Diagrammatic Sketch I. Discovered in 1898 by an Italian biologist Camillo Golgi, the Golgi Illustrating the Movement of Proteins from the ER to the ER-Golgi apparatus comprises of a series of oval, single membrane-bound flattened Intermediate Compartment (ERGIC) and then to the Golgi Apparatus discs with bulging ends called cistemae of about I µm in diameter, arranged in stacks. The number of stacks varies according to the type and function 5. The Golgi stacks are asymmetrical and consists of multiple distinct of cell. The number of stacks can go upto I 00 in some of the mammalian compartments referred to as cis, medial and trans Golgi stacks. The trans secretory cells. most Golgi cisternae form extensions that branch and anastomose into inter 2- Th_e series of cistemae, is called Golgi stack in animals and dictyosomes connected network called the Trans golgi network (TGN). (~ictus means "stack like") in plants. 6. The proteins enter through the convex cis Golgi network (entry face) which 3. Ci sternae margins of each Golgi stacks, are slightly curved to give the Golgi is usually oriented towards the nucleus and then progress to the medial and complex a bow-like appearance. concave trans compartments of the Golgi stack within which most metabolic 4 activities of the Golgi apparatus take place. The trans Golgi network TGN, · Th; co~vex end of the complex that is closer to ER is referred to as cis-face ~r onning face and the concave end comprise the trans-face or the maturing which acts as a sorting and distribution center, directing molecular traffic ,ace. of modified proteins, lipids and polysaccharides to endosomes, lysosomes, the plasma membrane or the cell exterior.  Electron... 29 Iof Cell Biology Study the Ultra Structural Details of Various Cellular Organelles Using Laboratory Manua... b. chemically different and hence the vesicl.cs down when required. (e) The actin filaments form a three dimensional 28. I.. t mac are ,o ribosome s iave to sequential! Each Golg1 c,s e. d by the bound 7. ·ns synthesise d·rr Y network at the periphery of the cell beneath the plasma membrane. This carrying protei. G lgi cistcrnae since these arc 1 1erently modified h the entire o. network determines the cell shape and movement. (D In plant cells the travel throug h' I contain different enzymes.. k. microfilaments are involved in numerous cellular functions including the. tcmae w ,c 1 k y role in the mod·r. 111cat1on, pac agmg and sorting in each c1s. atus plays a e. h I movement of organelles and cellular morphogenesis, which involve cell 8. Golg1 apparyr proteins.The Golgi apparatus re~e,_vdes} e nhew y synthesized division as well as the elongation and differentiation of the cell. of secrcto proteins and glycohp1 s trom t e ER and f-urther lecules- the gIyco. mac~omo m b O-linked glycosylat1on.. Minus end or th e. fy polysaccharides also takes place m the different modifies 11 point.cd end o ce 11 wa 9· The synthesists of Golgi apparatus. compartm~n. as polysaccharides are transportedh from.the Golgi teins hp1ds as we 11 way m various (;:, 'iJ (;:, P locations through the secretory pat 10. ro '... ~~ ___. appa ratus to various k1·nds of secretory ves1 ·c1es which are pinched off.from. transThGolg1 , h network t?~'i7 ___. co ___. 'iJ Ci). their. con tents to their respective destmat1ons. I e t ree major and dehver.. destmat1ons o sue secretory proteins. f h proteins are the plasma membrane, ysosomes and r G-actin , Dimer 'i7 1 Trimer Polymer Barbed end 4 2 or plus end Cytoskeleton (Fig. 4.1 O, 4 ·11 · 1 ) mprises of a network of proteinac eous fibersf that traverse I Cytos keIeton co. h · the cytop Iasm "rom the nucleus to the mner surface o t e plasma fig. 4.10 Assembly of Actin Filament by Polymerization of Actin Monomer s 11 ·ate the directed movemen ts of cell.and its contents.. (G· actin) to form Dimers, Trimers and Polymers mem brane an d medl It prov,'des th e structural framework to the cell anchoring proteins and of other macromolecules. Cellular components are moved around the cell 4. Microtubulcs (Fig. 4.11) (a) composed of heterodimeric subunits by the cytoskeleton during cytoplasmi~ streaming. ~ssembly of cell wall globular proteins a- and p. tubulin. (b) Tubulin dimers polymerize to components as well as their orientation 1s also determ1~ed by cytoskeleto~. form hollow straight columns called protofilaments, 25 nm in diameter. 2. The cytoskeleton includes three types of filaments: Actm filaments , Tubulm (c) 13 of such protofilaments assemble around a hollow core forming a filaments (Microtubules) and Intermediate filaments. The fila'.11ents a~e polar structure- microtubules. (d) Like actin filaments microtubules are composed of protein subunits that assemble to form poly':"enc protem dynamic structures that undergo polymerization and depolymerization filaments linked by non-covalent bonds. The assembly and disassembly of and can thereby undergo rapid cycles of assembly and disassembly. (e) these filaments are affected by factors such as pH, temperature and ionic They function to determine cell shape and are involved in a variety of cell strength.. movements like cell locomotion, intracellular transport of organelles as well 3. The main cytoskeletal protein of most cells is actin that polymerizes as separation of chromosomes during mitosis. is to form thin flexible fibers called microfilaments or actin filaments 5. Intermediate filaments (Fig. 4.12) (a) have a diameter of l 0-25 run that and tubulin filaments and hence the (Fig. 4.10) approximately 7nm in diameter and several micrometers in intermedi ate between that of the actin length with a distinct polarity. (a) Actin has two forms- G-actin (G stan~s name. (b) Unlike the other two elements of the cytoskeleton the intermediate for globular monomeric form) and the F-actin (F refers to the polymeric filaments have no direct role to play in cell movement and instead play filaments that are made up of several G-actin monomers). (b) Two parallel a structural role and provide mechanical strength to cells and tissues. actin filaments rotate at an angle of 166° around a helical axis to lie on (c) Intermediate filaments are composed of a variety of proteins that include top of each other creating a double helical structure of the microfilament. Iamins, karatins, vimentins etc. (d) Intennediate filaments associate with the (c)Actin filaments also associate into bundles or three-dimensional networks other members of the cytoskeleton and also with the plasma membrane thus wi! h the help of several associated proteins. (d) The actin polymerization providing a scaffold that integrates the components of the cytoskeleton as 15 a reversible dynamic process allowing the actin filaments to be broken well as organizes the internal structure of the cell.  Study the Ultra Structural Details of Various Cellular Organelles Using Electron... 31 Peroxisome I. Peroxisomes are a type of microbody present in plant cells. 2. Peroxisomes are single membrane bound organelles 0.2 - 1.Sµm in diameter and contain oxidative enzymes such as oxidase that forms H20 2, and catalase that breaks the Hi0 2 into H20 and 0 2. All peroxisomal enzymes are synthesised by free ribosomes. 3. Peroxisomes can easily be identified under electron microscope with sections that have been stained with diaminobenzidine as the latter fonns an electron-dense deposit in the presence of catalase. Peroxisomes are present in photosynthetic cells and function by consuming oxygen and removing hydrogen from organic substrates by removal of electrons and transferring them to 0 2: e RH 2 + 0 2 ~ R + H20 2 ( R=organic substrate) The peroxide produced in the reaction is potentially harmful to the cell and is broken down by the enzyme catalase present in the peroxisomes, liberating oxygen. H20 2 ~ H20 + 1/2 0 2 Fig. 4.11 Lateral and Cross Sectional View of the M' 4. Peroxisomes contain enzymes that function in (a) fatty acid oxidation, b 1crotu ules (b) metabolism of reactive oxygen species, (c) photorespiration and (d) triglyceride metabolism..a._ · Central rod domain 5. Peroxisomes in germinating seeds are responsible for the conversion of Polypeptide N 94f?A rt; - - - ~ stored fatty acids to carbohydrates, which is critical to providing energy and + ·~ C Head Tail raw materials for growth of the genninating plant. This occurs via a series Coiled-coil A of reactions tenned the glyoxylate cycle, which is a variant of the citric acid Dimer ~ t- I -- cycle. The peroxisomes in which this takes place are called glyoxysomes. 6. In legume root nodules, peroxisomes are involved in conversion of fixed + \: ::: le, f c nitrogen into nitrogen rich organic compounds. Tetramer t- DN Lysosomes (Fig. 4.13) Protofilament + I. Lysosomes are a type of microbody present in animal cells, are single + ·$ I membrane bound polymorphic bodies which vary in size, shape and ~.' I I ~ It I I :. F I ~ functions even within the same cell. 2. All lysosomes contain hydrolytic enzymes and the lysosomal membranes separate these enzymes from the rest of the cell thus protecting the cell from Filament these enzymes. Highly glycosylated integral proteins present (synthesised by the bound ribosomes) in the lysosomal membrane protect the membrane Fig. 4.12 Intermediate Filaments Assembly lnvo Ives th e Association of from the damage by the enclosed enzymes. Two Polypeptides that Wind Around Each 0 t h er In a coiled-co 11 3. Lysosomal enzymes are acid hydrolases that is, these are active at low Arrangement to form Dimers. The Dimers Associate. t O fOrm Tetramers d E ch pl-I and have a requirement of an acidic pH (4.5 or less) for their optimal.. and Protofilaments. Eight Proto fil am en t s Wound Aroun a activity. other to form Rope-like Intermediate Filaments  Manual of Cell Biology 32 Laboratory -- -.----==-=-=:--=.-:.~.:,:::,;:-,.~.-:--- >I. '. ,'4 , jlli"' i.1 " ,.~'. \ ~. I ~ Fig.4. 13 Electron Micrograph of an Autosome in whic h a Mitochondrlon and a Peroxisome have been Enclosed 4. The unique property of the lysosonrnl 1~1e mbrane is to maintain its internal acidic pH by actively accumulating H · ions (protons) with the help of u V-type proton pump. 5. There are three major types of lyso somes: (a) primary lysosomes (b) Secondary Lysosomes and (c) Residua l bodies. 6. Primary lysosomes are newly fanned and still virgin that is these have not entered into any hydrolytic pathway. Primary lysosomes originate from the Golgi complex and contain the hydrolytic enz ymes. 7. Secondary lysosomes are classified into two types namely (a) heterophagic vacuoles are also called heterosomes ·or phagos omes. These are formed by the fusion of the cytoplasmic vacuoles contain ing ex trace Ilular substances, received through endocytosis or phagocytos is. Fusion of the primary lysosomes with the heterosomes triggers the release of the hydrolytic enzymes leading to the digestion of the ingested materials. (b) Autophagic vacuoles (Fig. 4.13) also called autosomes con tain aged and non functional cellular organelles that are no longer required by the cells. These organelles are ~igested and contents released, the process 8· Resi known as autophagy. dual bodies contain undigested endocytosed th at are not material or parts of cells completely degraded in the secondary Iysosom released outside the cells es but are later 9. The Iysosomes l1. ave vari·ous functions like: (a) providin m ~~o_tozoa by phagocytosis, cellular g nutn·tion · s autophagy during unfavourable con ittons. (b) Defence against invading mic macrophages roorganisms by circulating and 11 fun ·. (c) Recyc 1mg - of cellular wastes and scavenging of age d on ctto nal organ II penetration · t e es. (d) Secretio. n of hydrolases by sperm for embryo (t) ~~ eg~. (e) Digestion of yolk 0 during the development of. issolut1on of blood clots and thrombi.