the cell


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the cell

  1. 1. Introduction to MolecularBiology
  2. 2. What is Molecular Biology?Study of biology at molecular levelBasic Molecular BiologyApplied Molecular Biology2
  3. 3. Which Molecular Level?• Nucleic AcidsDNARNA• Proteins3
  4. 4. What to know about nucleic acids?• StructureChemical propertiesPhysical propertiesTypes• Synthesis• FunctionBasic Molecular Biology4
  5. 5. 5
  6. 6. What to know about proteins?StructureChemical propertiesPhysical propertiesSynthesisHow the sequence of a protein is determined?GeneticsFunction of the proteinsStructure/Function RelationshipBasic Molecular Biology6
  7. 7. 7
  8. 8. 8The Central Dogma of Molecular Biology
  9. 9. Molecular biology seeks to explain therelationships between the structure andfunction of biological molecules and howthese relationships contribute to theoperation and control of biochemicalprocesses.9
  10. 10. Applications of MolecularBiology• Medicine• Agriculture• Pharmacy• Veterinary• Industry• Biological Sciences• etc10
  11. 11. • Medicine:BiochemistryParasitologyImmunologyBacteriologyVirologyPathologyLaboratory MedicineGeneticsetc.Applications of Molecular Biology(Molecular Medicine)11
  12. 12. Tools used in molecular studies• DNA cloningDNA cloning facilitates the isolation andmanipulation of fragments of an organism’sgenome by replicating them independentlyas part of an autonomous vector.Using Biological System12
  13. 13. • Polymerase Chain Reaction (PCR)PCR is used to amplify a sequence of DNA using a pair ofoligonucleotide primers each complementary to one endof the DNA target sequence.These are extended towards each other by a thermostableDNA polymerase in a reaction cycle of three steps:1. Denaturation2. Primer annealing3. PolymerizationUsing Chemical SystemTools used in molecular studies13
  14. 14. 14PCR MACHINES
  15. 15. • DNA SequencingThe two main methods of DNA sequencing are theMaxam and Gilbert chemical method andSanger’s enzymic method.• RNA Sequencing• Protein SequencingDATA BASESGenBankTools used in molecular studies15
  16. 16. 16
  17. 17. Some important events in thehistory of molecular biology1871 Discovery of the DNA.1943 DNA proves to be a genetic molecule capableof altering the heredity of bacteria :Avery, MacLeodand McCarty.1953 Postulation of a complementary double-helicalstructure for DNA.1960 Discovery of messenger RNA, and the demonstrationThat it carries the information that orders amino acidsin proteins. 17
  18. 18. DNA: The Transforming AgentIn 1943, Oswald Avery, C. M. MacLeod, and M. McCarty on bacteriumStreptococcus pneumoniae18
  19. 19. 19
  20. 20. 1961 Use of a synthetic messenger RNA moleculeto work out the first letters of the genetic code.Some important events in thehistory of molecular biology1966 Establishment of the complete genetic code.1970 Isolation of the first restriction enzyme, anenzyme that cuts DNA molecules at specific sites.1973 Beginning of DNA cloning in E. coli.1977 Formation of the first genetic engineering company(Genenetech) specifically found to use recombinant DNAmethods to make medically important drugs. 20
  21. 21. 1977 Development of procedures for the rapidsequencing of DNA.Some important events in thehistory of molecular biology1978 The Nobel Prize in Medicine was awarded for thediscovery and use of restriction enzymes to HamiltonSmith and Daniel Nathans.1978 Somatotatin becomes the first human hormoneproduced by using recombinant DNA.1980 The Nobel Prize in Chemistry is awarded dually tofor the formation of the first recombinant DNA molecules(Paul Berg) and thedevelopment of powerful methods for sequencing DNAto Gilbert and Gilbert and Sanger.21
  22. 22. 1981 Sickle-cell anemia becomes the first geneticdisease to be diagnosed antenatally directly atthe gene level by restriction enzyme analysis ofthe DNA.Some important events in thehistory of molecular biology1982 Human insulin produced by recombinant DNAmethods goes on the market under the trade nameHumulin.1985 Use of heat stable DNA polymerase in PCR.1990 First trial for gene therapy in humans22
  23. 23. THE CELL23
  24. 24. 24Cell TheoryCells were discovered in 1665 by Robert Hooke.Early studies of cells were conducted by- Mathias Schleiden (1838)- Theodor Schwann (1839)Schleiden and Schwann proposed the Cell Theory.
  25. 25. 25Cell TheoryCell Theory1. All organisms are composed of cells.2. Cells are the smallest living things.3. Cells arise only from pre-existing cells.All cells today represent a continuous line ofdescent from the first living cells.
  26. 26. 26Cell TheoryCell size is limited.-As cell size increases, it takes longer formaterial to diffuse from the cell membraneto the interior of the cell.Surface area-to-volume ratio: as a cellincreases in size, the volume increases10x faster than the surface area
  27. 27. 27Cell Theory
  28. 28. 28Cell TheoryMicroscopes are required to visualize cells.Light microscopes can resolve structuresthat are 200nm apart.Electron microscopes can resolvestructures that are 0.2nm apart.
  29. 29. Visualizing Cells29
  30. 30. 30Cell TheoryAll cells have certain structures in common.1. genetic material – in a nucleoid or nucleus2. cytoplasm – a semifluid matrix3. plasma membrane – a phospholipid bilayer
  31. 31. Cell Characteristics• Genetic material– single circular molecule of DNA inprokaryotes– double helix located in nucleus in eukaryotes– nuclear envelope (double membrane• Cytoplasm fills cell interior –– sugars, amino acids,– proteins - organelles• Plasma membrane encloses the cell phospholipid bilayerPhospholipidMembraneproteins 31
  32. 32. 32Prokaryotic CellsProkaryotic cells lack a membrane-boundnucleus.-genetic material is present in thenucleoidTwo types of prokaryotes:-archaea-bacteria
  33. 33. 33Prokaryotic CellsProkaryotic cells possess-genetic material in the nucleoid-cytoplasm-plasma membrane-cell wall-ribosomes-no membrane-bound organelles
  34. 34. 34Prokaryotic Cells
  35. 35. 35Prokaryotic CellsProkaryotic cell walls-protect the cell and maintain cell shapeBacterial cell walls-may be composed of peptidoglycan-may be Gram positive or Gram negativeArchaean cell walls lack peptidoglycan.
  36. 36. 36Prokaryotic CellsFlagella-present in some prokaryotic cells-used for locomotion-rotary motion propels the cell
  37. 37. 37Prokaryotic Cells
  38. 38. Generalized Eukaryotic Cell38
  39. 39. 39Eukaryotic CellsEukaryotic cells-possess a membrane-bound nucleus-are more complex than prokaryotic cells-compartmentalize many cellular functionswithin organelles and theendomembrane system-possess a cytoskeleton for support andto maintain cellular structure
  40. 40. The Plasma MembraneBADC40
  41. 41. The Plasma MembraneA. Phospholipid BilayerTwo layers of phospholipidsHydrophilic head groups facethe waterHydrophobic fatty acids face insideFatty acids may be saturated or unsaturated.Fatty acid structure is adjusted to keepmembranes fluid like oil, not solid like butter.A. CholesterolAdds rigidity to the membrane.Up to 30% of animal plasma membranes. 41
  42. 42. The Plasma MembraneC. ProteinsIntegral proteins span the membranePeripheral proteins are mostly on inside.Act as channels, transport, receptors, enzymesHelps to reinforce cell shapeD. Carbohydrates on the outsideGlycolipids—attached to phospholipidsGlycoproteins—attached to proteinsThe sugar chains form a sticky, sugar layer on theoutside of the plasma membrane called theglycocalyx.Used in mammals for cell-cell identification as partof immune system, such as blood types.42
  43. 43. 43Eukaryotic Cells
  44. 44. 44Eukaryotic Cells
  45. 45. 45Eukaryotic CellsNucleus-stores the genetic material of the cell inthe form of multiple, linear chromosomes-surrounded by a nuclear envelopecomposed of 2 phospholipid bilayers-in chromosomes – DNA is organized withproteins to form chromatin
  46. 46. 46Eukaryotic Cells
  47. 47. Chromosomes• DNA of eukaryotes is divided into linearchromosomes.– exist as strands of chromatin, except duringcell division– associated with packaging histones,packaging proteins• nucleosomes47
  48. 48. 48Eukaryotic CellsRibosomes-the site of protein synthesis in the cell-composed of ribosomal RNA andproteins-found within the cytosol of the cytoplasmand attached to internal membranes
  49. 49. 49Endomembrane SystemEndomembrane system-a series of membranes throughout thecytoplasm-divides cell into compartments wheredifferent cellular functions occur1. endoplasmic reticulum2. Golgi apparatus3. lysosomes
  50. 50. 50Rough endoplasmic reticulum (RER)-membranes that create a network ofchannels throughout the cytoplasm-attachment of ribosomes to themembrane gives a rough appearance-synthesis of proteins to be secreted, sentto lysosomes or plasma membrane
  51. 51. 51Smooth endoplasmic reticulum (SER)-relatively few ribosomes attached-functions:-synthesis of membrane lipids-calcium storage-detoxification of foreign substances
  52. 52. 52Endomembrane System
  53. 53. 53Golgi apparatus-flattened stacks of interconnectedmembranes-packaging and distribution of materials todifferent parts of the cell-synthesis of cell wall components
  54. 54. 54
  55. 55. 55Lysosomes-membrane bound vesicles containingdigestive enzymes to break downmacromolecules-destroy cells or foreign matter that the cellhas engulfed by phagocytosis
  56. 56. 56
  57. 57. 57Microbodies-membrane bound vesicles-contain enzymes-not part of the endomembrane system-glyoxysomes in plants contain enzymesfor converting fats to carbohydrates-peroxisomes contain oxidative enzymesand catalase
  58. 58. 58Vacuoles-membrane-bound structures with variousfunctions depending on the cell typeThere are different types of vacuoles:-central vacuole in plant cells-contractile vacuole of some protists-vacuoles for storage
  59. 59. 59MitochondriaMitochondrion-organelles present in all types ofeukaryotic cells-contain oxidative metabolism enzymes fortransferring the energy withinmacromolecules to ATP-found in all types of eukaryotic cells
  60. 60. 60Mitochondria-surrounded by 2 membranes-smooth outer membrane-folded inner membrane with layerscalled cristae-matrix is within the inner membrane-intermembrane space is located betweenthe two membranes-contain their own DNA
  61. 61. 61Mitochondria
  62. 62. 62Cytoskeleton-network of protein fibers found in alleukaryotic cells-supports the shape of the cell-keeps organelles in fixed locations-helps move materials within the cell
  63. 63. 63CytoskeletonCytoskeleton fibers include-actin filaments – responsible for cellularcontractions, crawling,-microtubules – provide organization tothe cell and move materials within the cell-intermediate filaments – provide structuralstability
  64. 64. 64Cytoskeleton
  65. 65. 65Cell MovementCell movement takes different forms.-Crawling is accomplished via actinfilaments and the protein myosin.-Flagella undulate to move a cell.-Cilia can be arranged in rows on thesurface of a eukaryotic cell to propel a cellforward.
  66. 66. 66Extracellular StructuresExtracellular structures include:-cell walls of plants, fungi-extracellular matrix surrounding animalcells
  67. 67. 67Cell walls-present surrounding the cells of plants,fungi, and some protists-the carbohydrates present in the cell wallvary depending on the cell type:-plant and protist cell walls - cellulose-fungal cell walls - chitin
  68. 68. 68Extracellular matrix (ECM)-surrounds animal cells-composed of glycoproteins and fibrousproteins such as collagen-may be connected to the cytoplasm viaintegrin proteins present in the plasmamembrane
  69. 69. 69Extracellular Structures
  70. 70. 70
  72. 72. Diffusion• Diffusion is the movement of moleculesfrom an area of higher concentration to anarea of lower concentration (which we call“down the concentration gradient”)• Random movement of molecules fills theavailable space.• Does not require cellular energy in theform of ATP.72
  73. 73. Factors Affecting DiffusionLess diffusion More diffusionCooler TemperatureWarmerLarger Molecule size SmallerSubstrate StateSolidSolid Liquid Gas73
  74. 74. Osmosis and TonicityOsmosis is diffusion across a semi-permeablemembrane.In cells, we usually compare water and saltconcentrations inside & outside the cell.Isotonic is salt concentrations same on bothsides of the membraneHypotonic (“less salty”): one side is less saltythan the other.Hypertonic (“very salty”): one side is more saltythan the other.74
  75. 75. Examples Using Red Blood CellsSaltier outsidethan inside: waterleaves cells,shriveling them.Saltier inside thanoutside: water enterscells, swelling them,sometimes tobursting.Salt conc. sameinside and out.Normal for cells.No net movementof water.75
  77. 77. Types of Transport Across Membranes1. Passive Transport substances movedown their concentration gradient2. Facilitated Diffusion— protein-assisteddiffusion3. Active Transport— substances moveagainst their concentration gradient;requires energy77
  78. 78. Passive Transport• Diffusion across a membrane down theconcentration gradient• Does not require cellular energy (ATP)• Usually pass through the lipid bilayer– Oxygen– Carbon dioxide– Small hydrocarbons (also hydrophobic)78
  79. 79. Facilitated TransportPassive transported assisted by proteinsGoes down concentration gradient and sodoes not require energy.For molecules that cannot easily passthrough lipid bilayer:◦ H2O◦ ions◦ glucose, etc.Osmosis with water occurs by facilitatedtransport using the protein aquaporin.79
  80. 80. Channel ProteinsChannel proteins are 1 of 2 types ofintegral membrane proteins in facilitateddiffusion.◦ Often made of 3 or more subunits (polypeptides)grouped together.◦ Have hydrophilic channel in the middle formolecules to pass through.◦ Specific for type of molecule: H2O, Ca++, etc.◦ Many are gated and require a chemical orelectrical stimulus to open the channel as in nervecells (neurons). 80
  81. 81. Examples of channel proteins81
  82. 82. Carrier Proteins• Carrier proteins are facilitated transportproteins that bring molecules across themembrane by changing shape in a rockingmotion.82
  83. 83. Active Transport• Carries molecules against theconcentration gradient• Requires energy usually as ATP.Ion pumps are active transport pumpsEstablish different concentrations of anionsand cations across membrane so set up acharge across the membrane or membranepotential.83
  84. 84. The Sodium-Potassium Pump84
  85. 85. Thanks 85