Chapt 02

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Chapt 02

  1. 1. GENERAL BIOLOGY HDL 121 CELL COMPONENTSPREPARED BY:MANEGASCHOOL OF MLTFACULTY OF HEALTH SCIENCE
  2. 2. CELL COMPONENTSChapter 2 : Cell ComponentsCourse PurposeThis course introduces animal cells based on structure,characteristics, functions and cellular division. It alsoemphasises the theory of inheritance including the structureand role gene, DNA, and chromosome. Slide 2 of 10 © 2010 Cosmopoint
  3. 3. CELL COMPONENTSChapter 2 : Cell ComponentsTopic Outlines 2.1 Fluid Mosaic Model 2.1.1 Proposed by Singer & Nicholson 2.1.2 Functions of cell membrane 2.1.3 Connection between cells 2.1.4 Special Structure 2.2 Connection between cells 2.2.1 Tight Junction 2.2.2 Desmosome 2.2.3 Gap Junction 2.3 Special structure 2.3.1 Microvilli Slide 3 of 10 © 2010 Cosmopoint
  4. 4. CELL COMPONENTSChapter 2 : Cell ComponentsLearning Outcomes After completing this lecture, students will be able to: (a) Describe the structure of cell membrane – recall the fluid mosaic model (b) List the functions of cell membrane (c) Outline the membrane junctions – tight junction, gap junction & desmosome (d) Explain special structures of cell membrane, the microvilli Slide 4 of 10 © 2010 Cosmopoint
  5. 5. CELL COMPONENTSChapter 2 : Cell ComponenetsSub Topic 2.1 : Fluid Mosaic Model Lipoprotein layer that surrounds the cell & organelles eg. nucleus, mitochondria, chloroplast, vacuole & lysosome. The structure of the membrane is based on Singer & Nicolson’s fluid-mosaic model Slide 5 of 10 © 2010 Cosmopoint
  6. 6. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.1 : Proposed by Singer & Nicholson The basic structure of membrane consists of a bimolecular phospholipid fluid layer (2 layers of phospholipids/phospholipid bilayer) with globular protein units floating in it forming a mosaic pattern The heads of the phospholipid are hydrophilic pointing outwards into the aqueous medium on both sides of the membrane The tails of phospholipid are hydrophobic facing each other & forming a non-polar interior in the middle of the membrane The structure is dynamic, each lipid molecule can move within its own monolayer and so is each of the protein unit. Some protein units are immobilised by microfilament with the interior of the cell Slide 6 of 10 © 2010 Cosmopoint
  7. 7. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.1 : Proposed by Singer & Nicholson Slide 7 of 10 © 2010 Cosmopoint
  8. 8. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.1 : Proposed by Singer & Nicholson The fluidity of the membrane depends on the length of the fatty acid chains, their saturation & the amount of cholesterol among them. Fluidity affects permeability, membrane enzyme activities, reception to molecules & ease with which membranes fuse Cholesterol with its hydrophilic head & hydrophobic tail fits neatly within the phospholipid layer It functions to control mechanical stability, flexibility & permeability of membrane, particularly reduced leakage of small polar molecules The proteins are embedded in the phospholipid layer like mosaic, only in one monolayer or span the whole membrane. These are integral or intrinsic proteins, fitted neatly because of their charged properties on their surfaces. Slide 8 of 10 © 2010 Cosmopoint
  9. 9. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.1 : Proposed by Singer & NicholsonThe peripheral or extrinsic ones are attached on the outer polarlayer of phospholipidThe proteins function as carriers or channels for molecules tocross the membrane, as structural components, enzymes,receptors & electron carriers for respiratory or photosyntheticphosphorylationsThe carbohydrates exists as branched short chain of sugars onthe outer surface of membranei. glycoproteins (CHO + proteins)ii.glycolipids (CHO + lipids)Function:i. as receptors for chemical like hormonesii.adhesion to neighbouring cells & for immune responses Slide 9 of 10 © 2010 Cosmopoint
  10. 10. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.1 : Proposed by Singer & Nicholson Slide 10 of 10 © 2010 Cosmopoint
  11. 11. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.1 : Proposed by Singer & Nicholson Slide 11 of 10 © 2010 Cosmopoint
  12. 12. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.1 : Proposed by Singer & Nicholson Slide 12 of 10 © 2010 Cosmopoint
  13. 13. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.2 : Functions of cell membrane 1.Barrier/Boundary – physically separates the intracellular components from the extracellular environment (substances outside do not affect reactions taking place within the cell) 2.Anchor – peripheral proteins anchor the cytoskeleton to provide shape to the cell & in attaching to the extracellular matrix to help group cells together in the formation of tissue 3.Transport /regulates or controls the passage – phospholipid bilayer is selectively permeable, allows only certain molecules to pass through protein channels allow only specific polar molecules to go in or out Slide 13 of 10 © 2010 Cosmopoint
  14. 14. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.2 : Functions of cell membrane 4.Receptor sites – some integral proteins as receptor/binding sites for hormones (for recognising external stimuli i.e hormone & antigen molecules – enables cells to recognise other cells & to behave in an organised manner during formation of tissue in the embryo 5.Identification – Glycoproteins as marker, recognized by other cells 6.Protection – any chemical/reaction that happened outside would not harm the cell Slide 14 of 10 © 2010 Cosmopoint
  15. 15. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.1.2 : Functions of cell membrane 7. Compartmentalisation – Within cells, membranes allow compartmentalisation & division of labour to occur especially within membrane-bound organelles. 8. Special functions: light reaction in the membrane of chloroplast & oxidative phosphorylation in the inner membrane of mitochondria 9. Cell Mobility (eg. WBC) & communication between cells Slide 15 of 10 © 2010 Cosmopoint
  16. 16. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic : 2.2 Connection between cells 3 major types: (a) Tight junction (b) Gap junction (c) Desmosome Slide 16 of 10 © 2010 Cosmopoint
  17. 17. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.2.1 :Tight Junction Composed of protein fibres that seal adjacent cells to prevent leakage Forms impermeable junction Eg. Bladder & the lining of the digestive tract Slide 17 of 10 © 2010 Cosmopoint
  18. 18. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.2.1 :Tight Junction Slide 18 of 10 © 2010 Cosmopoint
  19. 19. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.2.2: DesmosomeOn inner surface of cell membrane are specialized integralproteins called plaquesPlaques from adjacent cells connected by thin linker filament(special protein called cadherins)Similar to rivets or staples that attach to components of thecytoskeletonMany epithelial cells must adhere to adjacent membranes toprevent free passage or free movement & to not break apartunder stress Slide 19 of 10 © 2010 Cosmopoint
  20. 20. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.2.2: Desmosome Slide 20 of 10 © 2010 Cosmopoint
  21. 21. CELL COMPONENTSChapter 2 : Cell ComponentsSub Topic 2.2.2: Desmosome Slide 21 of 10 © 2010 Cosmopoint
  22. 22. CELL COMPONENTSChapter 2 : Cell MembraneSub Topic 2.2.3: Gap JunctionAlso known as nexusAt gap junction, the cell membranes of adjacent cells are verycloseTransmembrane proteins form specialized structures of hollowcylinder (protein channel) called connexonsConnexons allow transfer of chemical / small molecules(nutrient monomers) between the cellsCommon in brain cells, forming the synapse, in many glands &in cells in the heart muscle that coordinate contraction forheartbeat. Slide 22 of 10 © 2010 Cosmopoint
  23. 23. CELL COMPONENTSChapter 2 : Cell MembraneSub Topic 2.2.3: Gap Junction Slide 23 of 10 © 2010 Cosmopoint
  24. 24. CELL COMPONENTSChapter 2 : Cell MembraneSub Topic 2.3 : Special Structure Found in absorptive cells Eg. Cells lining the small intestines (microvilli), cells in Loops of Henle. Microvilli are formed as cell extensions from the plasma membrane surface. Function: to increase the surface area for absorption Slide 24 of 10 © 2010 Cosmopoint
  25. 25. CELL COMPONENTSChapter 2 : Cell MembraneSub Topic 2.3.1 : Microvilli MICROVILLI Slide 25 of 10 © 2010 Cosmopoint
  26. 26. CELL COMPONENTS1.1. Cytoskeleton = cell inclusions Definition: cellular ‘scaffolding’ or ‘skeleton’ contained within the cytoplasm A dynamic structure that maintains cell shape, structural integrity & cell & organelle motility Determines the 3 dimensional shape of the animal cells & give a certain firmness in the plant cells 3 elements of cytoskeleton: (a) microfilament (b) microtubule (c) intermediate filament Slide 26 of 10 Topics
  27. 27. CELL COMPONENTS1.1.1:Definition, elements of cytoskeleton (microfilament, microtubule, intermediate filament) Slide 27 of 10 Topics
  28. 28. CELL COMPONENTS1.1.1:Definition, elements of cytoskeleton (microfilament, microtubule, intermediate filament) Slide 28 of 10 Topics
  29. 29. CELL COMPONENTS1.2 : MicrofilamentStructure - fine filaments made of protein with a diameter of 7 nm & a length of several µm - composed of one / two types of protein including actin & myosin - dynamic  can change their length very quickly depending on their locations & functions - each type of protein forms subunits that are arranged helically - the subunits can slide over one another causing the microfilament to contract Slide 29 of 10 Topics
  30. 30. CELL COMPONENTS1.2.1 Structure, position in cells, functionsPosition in cells - exist in bundles & normally found in layer in cytoplasmFunctions - cause invagination & evagination of membrane during endocytosis & exocytosis - cause protrusion of pseudopodium during amoeboid movement in white blood cells - assist in the cleavage process during cytokinesis of animal cells after nuclear division Slide 30 of 10 Topics
  31. 31. CELL COMPONENTS1.2.1 Structure, position in cells, functions Illustrated in Figure 2 is a fluorescence digital image of an Indian Muntjac deer skin fibroblast cell stained with fluorescent probes targeting the nucleus (blue) and the actin cytoskeletal network (green). Slide 31 of 10
  32. 32. CELL COMPONENTS1.3 Microtubule  Structure - fine unbranched tubules with diameter of 25 nm, a wall of 5 nm thick & vary in length - the wall composes 13 rows of globular protein subunits called tubulin, which arranged helically in the wall - tubulin can grow from a certain organisation centre, which is made of dense protein. - tubulin can be added at the base or at one end of microtubule causing to increase in length / removed, causing it to decrease in length Slide 32 of 10
  33. 33. CELL COMPONENTS1.3.1 Structure, position in cells, functions, centrosome & centriole(structure, position in cells, functions) Slide 33 of 10
  34. 34. CELL COMPONENTS1.3.1 Structure, position in cells, functions, centrosome & centriole(structure, position in cells, functions)  Functions - form the cytoskeleton that determines the shape of the cell - divide the cytoplasm into compartments  specialized enzyme system can be isolated from others to function better - can contract causing movement in the cilia & flagella - can pull chromosomes / chromatids during mitosis or meiosis - cause the movement of organelles including mitochondria, lysosomes & vesicles along them like railway tracks Slide 34 of 10
  35. 35. CELL COMPONENTS1.3.1 Structure, position in cells, functions, centrosome & centriole(structure, position in cells, functions) Centrosome & Centriole microtubule organizing centre is an area in the cell where microtubles are produced. Within an animal cell centrosome there is a pair of small organelles, the centrioles, each made up of a ring of nine groups of microtubules. There are three fused microtubules in each group. The two centrioles are arranged such that one is perpendicular (90°) to the other. Slide 35 of 10
  36. 36. CELL COMPONENTS1.3.1 Structure, position in cells, functions, centrosome & centriole(structure, position in cells, functions)  During animal cell division, the centrosome divides and the centrioles replicate (make new copies).  The result is two centrosomes, each with its own pair of centrioles.  The two centrosomes move to opposite ends of the nucleus, and from each centrosome, microtubules grow into a "spindle" which is responsible for separating replicated chromosomes into the two daughter cells. Slide 36 of 10
  37. 37. CELL COMPONENTS1.3.1 Structure, position in cells, functions, centrosome & centriole(structure, position in cells, functions) Slide 37 of 10
  38. 38. CELL COMPONENTS1.3.1 Structure, position in cells, functions, centrosome & centriole(structure, position in cells, functions) Slide 38 of 10
  39. 39. CELL COMPONENTS1.4 :Intermediate filament Structure - filament bigger than the microfilament but smaller than the microtubule, diameter between 8 to 12 nm, only found in animal cells - made up of 4 long stands α-helix coiled fibrous proteins, each consists of only secondary coiled polypeptide - several types; each composes of only one type of protein, including one with keratin - very stable Slide 39 of 10
  40. 40. CELL COMPONENTS1.4.1 Structure, position in cells, functions Slide 40 of 10
  41. 41. CELL COMPONENTS1.4.1 Structure, position in cells, functions  Position of cells - branched & formed a network of cytoskeleton in the cytoplasm & nucleus  Functions - maintain the shape of the cell including nucleus - distribute the organelles & support them in the cytoplasm - help some specialised cells to perform their functions. Eg. The nail producing cells to form the nail & neuron to transmit impulse Slide 41 of 10
  42. 42. CELL COMPONENTS1.4.1 Structure, position in cells, functions Slide 42 of 10
  43. 43. CELL COMPONENTS1.5. Cytoskeletal projection Cilia & flagella are projections form the cell, have the same internal structure but with the different length They are made up of microtubules Slide 43 of 10
  44. 44. CELL COMPONENTS1.5.1 Definition, example – cilia, flagella, basic structure of cilia &flagella Flagellum  A flagellum (plural: flagella) is a long, slender projection from the cell body  The main differences among these three types of flagella: (a) Bacterial flagella: helical filaments that rotate like screws. They provide bacterial motility (b) Archaeal flagella are superficially similar to bacterial flagella, but are different in many details & considered non-homologous (c) Eukaryotic flagella: those of animal, plant & protist cells are complex cellular projections that lash black & forth Slide 44 of 10
  45. 45. CELL COMPONENTS1.5.1 Definition, example – cilia, flagella, basic structure of cilia &flagella An eukaryotic flagellum is a bundle of nine fused pairs of microtubule doublets surrounding two central single microtubules Slide 45 of 10
  46. 46. CELL COMPONENTS1.5.1 Definition, example – cilia, flagella, basic structure of cilia &flagella Slide 46 of 10
  47. 47. CELL COMPONENTS1.5.1 Definition, example – cilia, flagella, basic structure of cilia &flagella Cilium An organelle found in eukaryotic cells Made up of microtubules Tail-like projections extending approximately 5-10 µm outwards from the cell body Two types of cilia (a) motile: constantly beat in a single direction (b) non-motile: typically serve as sensory organelles Slide 47 of 10
  48. 48. CELL COMPONENTS1.5.1 Definition, example – cilia, flagella, basic structure of cilia &flagella Slide 48 of 10
  49. 49. CELL COMPONENTS1.5.1 Definition, example – cilia, flagella, basic structure of cilia &flagella The primary purpose of cilia in mammalian cells is to move fluid, mucous or cells over their surface In humans, ie. Motile cilia are found in the lining of the trachea (windpipe), where they sweep mucus & dirt out of the lungs In female mammals, the beating of cilia in the Fallopian tubes moves the ovum from the ovary to the uterus Slide 49 of 10
  50. 50. CELL COMPONENTSCytosol Definition: the liquid medium of the cytoplasm which is viscous & transparent / soluble part of cytoplasm = ground substance Consists of approximately 75 – 90% water plus ions & many types of organic molecules eg. Enzymes Cytoplasm minus organelles & insoluble components e.g mitochondria 9/21/2011 50 Slide 50 of 10
  51. 51. CELL COMPONENTS Functions: - stores vital chemicals including fats - as the site for certain metabolic pathways (eg. glycolysis, synthesis of fatty acids & amino acids) - as the medium in which many intracellular chemical reactions occur - enables organelles (mitochondria, chloroplasts, ribosomes, lysosomes & vacuole) to move about in it. 9/21/2011 51 Slide 51 of 10
  52. 52. CELL COMPONENTSOrganelles Organelles in cytoplasm include (a) mitochodria (b) ribosomes (c) chloroplasts (d) lysosomes (e) vacuoles (f) Golgi apparatus (g) endoplasmic reticulum 9/21/2011 52 Slide 52 of 10
  53. 53. CELL COMPONENTS Definition: structures within the cell that are specialized for particular functions Basic structure - most organelles have membranes that are very similar to the plasma membrane - the membrane effectively separate the organelle from the cytosol 9/21/2011 53 Slide 53 of 10
  54. 54. CELL COMPONENTSMitochondria Basic structure: - spherical, filamentous or rod-shaped bodies which are bound by a double membrane (outer & inner) - Size: 2 – 8 µm in length - The outer membrane is smooth in texture & surrounds the mitochondrion itself - The inner membrane is arranged in a series of folds known as cristae - The central cavity of the mitochondria which is enclosed by the inner membrane & the cristae is called the matrix 9/21/2011 54 Slide 54 of 10
  55. 55. CELL COMPONENTS Distribution: - found in every eukaryotic cell - the location inside the cell in not fix, they can move - protozoa & yeasts have only one mitochondrion per cell. - In liver cell  500 – 1400 per cell 9/21/2011 55 Slide 55 of 10
  56. 56. CELL COMPONENTS 9/21/2011 56 Slide 56 of 10
  57. 57. CELL COMPONENTS Functions of mitochondria (a) carry out Krebs cycle part of cellular respiration within their matrise (b) carry out oxidation of fatty acids & amino acids (c) carry out oxidative phosphorylation, which produces ATP from ADP & phosphate principal sites for the generation of cellular energy (ATP) during cellular respiration; ‘power houses’ (d) produce their own proteins from DNA with the aid of RNA 9/21/2011 57 Slide 57 of 10
  58. 58. CELL COMPONENTS Definition:Ribosomes small granules where synthesis of proteins occurs Distribution: - found in all cells particularly cells that produce a lot of proteins (eg. Glandular cells of the pancreas & liver cells). - found in the nucleus, cytoplasm freely or attached to ER, mitochondria & chloroplasts. - their numbers is not fixed 9/21/2011 58 Slide 58 of 10
  59. 59. CELL COMPONENTS 9/21/2011 59 Slide 59 of 10
  60. 60. CELL COMPONENTS Basic Structure: - spheroid in shape, consisting of two subunits, one is larger than the other - Very small, ~ 20 nm in diameter for 80S (eukaryotic) & smaller for 70S (prokaryotic) - The subunits can be attached to form bigger functional units in the presence of magnesium ion. Eukaryote: 60S + 40S  80S Prokaryote: 50S + 30S  70S - made up of RNA & protein synthesized in the nucleolus 9/21/2011 60 Slide 60 of 10
  61. 61. CELL COMPONENTS Functions: - provide site for the formation of peptide bonds - amino acids are joined together to form polypeptide / protein. - the subunits can form complex with mRNA - two sites are provided on the surface where tRNA would bring two amino acids to the sites matching the codon of mRNA to that of anti-codon of the tRNA. - ribosomes can ‘read’ the codes on the mRNA & join specific sequence of amino acids to form specific protein 9/21/2011 61 Slide 61 of 10
  62. 62. CELL COMPONENTSEndoplasmic Reticulum (ER) Basic structure: - formed by a complex system of membranes forming tubes & branching channels through the cytoplasm - can be divided into two types (a) Rough ER – with ribosomal attachments on its outer surface, found in glandular cells that produce a lot of protein for secretion (eg. Digestive system  pacrease, stomach) (b) Smooth ER – lacks ribosomal attachments, embedded on the inner surface of the membrane, there are a lot of enzymes catalysing the synthesis of CHO & lipids 9/21/2011 62 Slide 62 of 10
  63. 63. CELL COMPONENTS 9/21/2011 63 Slide 63 of 10
  64. 64. CELL COMPONENTS Functions: - differentiated largely based on the presence or absence of attached ribosomes. - Rough ER  produce proteins for secretion & also for internal use. Eg. Digestive enzyme, hormones & antibody.  transports proteins to smooth ER / Golgi apparatus through sacs pinched off from its surface membrane. Eg. Protein like mucus has its CHO component added in the smooth ER or Golgi apparatus. 9/21/2011 64 Slide 64 of 10
  65. 65. CELL COMPONENTS - Smooth ER  synthesis, secrete & store lipids, CHO & other non- protein product  participates in the detoxification process of harmful chemicals  forms lysosomes; vesicles that are used for internal transport & reactions 9/21/2011 65 Slide 65 of 10
  66. 66. CELL COMPONENTSGolgi Apparatus = Golgi body or Golgi complex & found universally in both plant & animal cells Basic structure: - consists of flat vesicular discs structures placed one on top of the other, which can produce vesicles full of secretion for internal & external uses - proteins made within rough ER bud off in vesicles will be transported to the Golgi where the vesicle fuse with the membrane - the components are then modified & packaged by the time they bud off as vesicle 9/21/2011 66 Slide 66 of 10
  67. 67. CELL COMPONENTS 9/21/2011 67 Slide 67 of 10
  68. 68. CELL COMPONENTS Distribution - found in large no. in glandular cells, neurones * muscle cells. - locations within the cell are not fix, can move & formed form ER - usually one per cell Functions - modifies, packages & distributes all proteins (form glycoprotein) & lipids (form glycolipids) for export & storage - forms lysosomes through the budding of larger vesicle or fusion of several smaller ones. 9/21/2011 68 Slide 68 of 10
  69. 69. CELL COMPONENTSLysosome Basic structure: - spherical membrane bound vesicles containing hydrolytic enzyme that can digest most biological macromolecules - size: 0.05 to 0.50 µm in length - the limiting membrane keeps the digestive enzymes separated from the cytoplasm (Eg. Protease, lipase) - contain digestive hydrolases 9/21/2011 69 Slide 69 of 10
  70. 70. CELL COMPONENTS - These enzymes function optimally at pH 5 & inactive at cytosol pH (pH 7.2) - together with the limiting membrane, this will protects the cell from digesting itself Distribution - found in cells that carry out endocytosis (eg. WBC & protozoa) - found in animal cells, absent in plant cells 9/21/2011 70 Slide 70 of 10
  71. 71. CELL COMPONENTS Functions: - Carry out intracellular digestion (phagocytosis) in which plasma membrane engulf substances & pinch off to form a particle-containing vacuole. Lysosome fuse with the vacuole & digest with their hydrolytic enzyme - Carry out program cell destruction (autolysis) 9/21/2011 71 Slide 71 of 10
  72. 72. CELL COMPONENTS < Electron micrograph of lysosomes Lysosome in the process of destroying a membrane bound mitochondrion > 9/21/2011 72 Slide 72 of 10
  73. 73. CELL COMPONENTS 9/21/2011 73 Slide 73 of 10
  74. 74. CELL COMPONENTS 1. Vesicles containing materials from outside the cell are taken into the cell 2. The vesicle is pinched off from the plasma membrane & becomes a separate vesicle 3. A lysosome approaches the vesicle 4. The lysosome fuses with the vesicles 5. The enzyme from the lysosome mix with the material in the vesicle & the enzymes digest the material 9/21/2011 74 Slide 74 of 10
  75. 75. CELL COMPONENTSNucleus Largest membrane-enclosed organelle in the eukaryoric cell, diameter 10 -20 µm Normally it is spherical or oval in shape; may be cylindrical or lobed in the WBC. The shape can be changed Distribution: found in the centre of the cell but in matured plant cells, it is pushed one side of the protoplast by the big sap vacuole. Normally one per cell Slide 75 of 10 Topics
  76. 76. CELL COMPONENTS1.1.1: Basic structure & FunctionsIt is found in all cells, except in the red blood cells & sieve tubesof phloemContains most of the cell’s genetic material, organized asmultiple long linear DNA molecules in complex with a large varietyof proteins (eg. histones) to form chromosomesFunction: to control all the activities of the cell by regulatinggene expression and to maintain the integrity of these gene Slide 76 of 10 Topics
  77. 77. CELL COMPONENTS1.2. Nucleus parts or componentsThe nucleus can be divided into (a) nuclear envelope (b) nucleoplasm (c) nucleolus (d) chromosome Slide 77 of 10 Topics
  78. 78. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus,nucleoplasm, chromatin / chromosome, DNA)Nuclear envelopeDouble lipoprotein membrane that encloses the entire organelle & keeps its contents separated from the cellular cytoplasmConsists of two cellular membranes, an inner & an outer membrane, arranged parallel to one another & separated by 10 – 50 nmThe inner membrane is smooth; no ribosome is attached to it & is not folded. This envelope disappears at prophase of cell division & reappears at the end of it. Slide 78 of 10 Topics
  79. 79. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus,nucleoplasm, chromatin / chromosome, DNA)The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER) & is similarly studded with ribosomesSometimes, it may be continuous right to the plasma membraneThe space between the membranes (about 10 – 40 nm) is called the perinuclear space & is continuous with the RER lumen Slide 79 of 10 Topics
  80. 80. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus,nucleoplasm, chromatin / chromosome, DNA)  Nuclear pores, which provide aqueous channels through the envelope, are composed of multiple proteins, collectively referred to as nucleoporins  The pores are relatively big, 40 -150 nm & covered a surface of 8% of the envelope  Passage of substances is very controlled  allows the free passage of small water-soluble molecules while preventing larger molecules (eg. nucleic acids & proteins) from inappropriately entering or existing the nucleus  These large molecules must be actively transported into the nucleus instead. Slide 80 of 10
  81. 81. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA)Nuclear pore 1. Nuclear envelope. 2. Outer ring. 3. Spokes. 4. Basket. 5. Filaments. (Drawing is based on electron microscopy images) Slide 81 of 10
  82. 82. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Functions of nuclear envelope  It protects the inner structures of the nucleus  It separates the nucleus from the cytoplasm / separates the cell’s genetic material from the surrounding cytoplasm  reactions occur in the nucleus are not affected  It controls the shape of nucleus  It controls the passage of substances from & to nucleus / serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm & the cytoplasm Slide 82 of 10
  83. 83. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Nucleoplasm Nuclear sap / karyoplasm Part of protoplasm that is inside the nucleus Its composition – same as cytoplasm  consisting mainly water with crystalloids & colloids dissolved in it Has DNA, histone & pentoses that are not found in the cytoplasm Easily stained with acidic eosin to form purple colour Slide 83 of 10
  84. 84. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Crystalloids: monosaccharides, amino acids, organic acids, nucleotides & mineral ions Colloids: DNA, RNA & proteins particularly histone that mixed with DNA forming chromatins Slide 84 of 10
  85. 85. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Functions of nucleoplasm Contains various enzymes for metabolism including that for glycolysis, Krebs cycle, phosphorylation & synthesis of NAD, replication & transcription of DNA Slide 85 of 10
  86. 86. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Chromatin  Describes nuclear material that contains the genetic code  The code is stored in individual units called ‘chromosomes’  The complex of DNA & protein that makes up chromosomes  It is found inside the nuclei of eukaryotic cells, & within the nucleoid in prokaryotic cells  The major proteins involved in chromatin are histone proteins, although many other chromosomal proteins have prominent roles too Slide 86 of 10
  87. 87. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Changes in chromatin structure are affected mainly by methylation (DNA & proteins) & acetylation (proteins) The functions of chromatin are to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis & meiosis & to serve as a mechanism to control expression Chromatin structure is also relevant to DNA replication & DNA repair Slide 87 of 10
  88. 88. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Two types of chromatin can be describes: (a) Heterochromatin (b) Euchromatin Slide 88 of 10
  89. 89. CELL COMPONENTS 1.2.1 Structure and functions (nuclear envelope, nucleolus,nucleoplasm, chromatin / chromosome, DNA) Slide 89 of 10
  90. 90. CELL COMPONENTS 1.2.1 Structure and functions (nuclear envelope, nucleolus,nucleoplasm, chromatin / chromosome, DNA) Nucleolus Spherical structure that is the site of ribosome synthesis in interphase nucleus It is not surrounded by a membrane & is sometimes called suborganelle It forms around tandem repeats of rDNA, DNA coding for ribosomal RNA (rRNA) The main roles of the nucleolus are to synthesize rRNA & assemble ribosomes Slide 90 of 10
  91. 91. CELL COMPONENTS 1.2.1 Structure and functions (nuclear envelope, nucleolus,nucleoplasm, chromatin / chromosome, DNA) The transcription, post-transcriptional processing & assembly of rRNA occurs in the nucleolus The assembled ribosomal subunits are the largest structures passes through the nuclear pores Nucleolus disappears during cell division but reappears in the final stage of mitosis Slide 91 of 10
  92. 92. CELL COMPONENTS 1.2.1 Structure and functions (nuclear envelope, nucleolus,nucleoplasm, chromatin / chromosome, DNA) Chromosome  Functions: - control the production of RNA & proteins in cells. Through these RNA & proteins (enzymes), chromosomes control all the activities of the cell & inheritable characters of an organism - compact chromosomes  enable mitosis & meiosis. Such forms can move easily compared to untidy long slender DNA  enable genes to be passed down from one mother cell to daughter cells & one generation to the next generation Slide 92 of 10
  93. 93. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Slide 93 of 10
  94. 94. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA)DNAA nucleic acid that contains the genetic instructions used in the development & functioning of all known living organismsMain role: long term storage of informationLong polymere of simple units called nucleotides, with a backbone made of sugars & phosphate groups joined by ester bondsAttached to each sugar is one of four types of molecules calles bases Slide 94 of 10
  95. 95. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) Slide 95 of 10
  96. 96. CELL COMPONENTS1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,chromatin / chromosome, DNA) It is the sequence of these four bases along the backbone that encodes information This information is read using the genetic code, which specifies the sequence of the amino acids within proteins The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription Within cells, DNA is organized into structures called chromosomes Slide 96 of 10
  97. 97. CELL COMPONENTS Slide 97 of 10 Topics

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