Overview of the cell structure Overview of the cell structure

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Transcript of Overview of the cell structure Overview of the cell structure

  • Overview of the cell structure

  • Readings and ObjectivesReadingRussell: 2.5a, 21.2, 22Cooper: Chapter 1ObjectivesCell TheoryBasic properties of cellsCell sizeCell diversityProkaryotic vs eukaryotic cells DiversityStructure

  • Properties of CellsBasic properties of cellsOrder and complexitysurrounded by a semi-permeable membrane, similar in composition and functionSimilar chemical composition: similarity of structural patterns of macromolecules and their functionsSimilar biochemical and regulatory processeshierarchal complexity from molecules to supramolecular structures Self replication by division: all cells come from existing cells by division, process of division share similarities among cells

  • Properties of CellsBasic properties of cellsCells are small (see module 3)Varied between ~0.5 to a few 100 um (eg E.coli ~0.6 um, RBC 8 um, skin epithelial cells ~30 nm and ameoba ~500 um)Why cells are generally small? Limiting factor: Surface to volume ratio (S/V)Surface is the portal of supply for the volume of cell

  • Properties of CellsBasic properties of cellsCells are small (see module 3)S/V vs X in nonlinearS/V exponentially reduced as X increasesSurface (size of cell) reaches a limit that cannot support the cells need (volume)Eukaryotes: have increased the S/V by extending internal membrane surfaces

  • Properties of CellsPropertiesInteraction with the environmentAll have transmittable genetic programDNA: similar structure and function, being inheritedGenes: units of genetic function, basic similarityEvolution: plasticity of genetic information, functional divergence in response to environmental cuesEnergy biogenesisSimilarity of metabolic pathways, eg. glycolytic pathway, Krebs cycle, adaptive variations on a general themeUse of ATP as the universal cellular energy currencyChemical and mechanical activitySimilar enzymes carry out metabolic reactions energy Use of energy to do mechanical work

  • Cell theoryEarly observationsRobert Hooke (1665): first to observe unit structures in cork, called them cellsAntone Van Leeuwenhoek: discovers microbial single cellsMatthias Schleiden and Theodor Schwann (1839): Independently concurred that all living organisms,All living organisms consist of unit structures called Cells (The Cell theory)Rudolf Virchow (1855): expanded the cell theory, Each cell is the result of division of previous cellsModern cell biology addresses the question how cells workTo understand the molecular basis of cellular processes

  • Cell diversityDomains of life: cells are organized in three domainsProcaryotes- Eubacteria and ArhaebacteriaEucaryotes- Protista, Fungi, Plants and AnimalsSimilarities: Procaryotes and eucaryotesCell membrane energy metabolismGenetic codeDifferences: Procaryotes are unicellularExcept for many members of protista the rest of eukaryotes are multicellularSize: procaryotes 0.5-5 um, eucaryotes 5-500 umMembrane bound organelles present in eucaryotes but not procaryotesReproduction: cell fission in procaryotes vs mitosis in eukarotes

  • Procaryotes: StructureBacterial cytoplasm is surrounded by a cell membrane, a cell wall, and for some with a polysaccharide capsuleCell wall: used for protection, shape, rigidityComposed of peptidoglycan, a polysaccharide of alternating acetlylated muramic acid and glucoseamine 14 glycosidic bond btw sugars cross-linked by a short oligopeptide Two types of bacteria based on cell wall structureGram positive: multiple layers of peptidoglycan Gram negative: few layers of peoptidoglycan

  • Procaryotes: StructurePlasma membraneBeneath the cell wall is the plasma membrane, a phospholipid bilayer with associated proteins Steroid like molecules instead of cholesterol

  • Procaryotes: StructureCytoplasm: lacks membrane bound organellesRibosomes 70S; 3 rRNA + 55 proteins (in 2 subunits 50S and 30S)Protein synthesisChromosome: single supercoiled chromosome that resides in a region called nucleoid (not membrane bound)

  • Procaryotes: StructureBacteria have appendages with specific functions Flagella, composed of flagellin helps bacteria move Fimbriae are small bristlelike fibers that allow bacteria to attach themselves to surfaces Sex pili (F pilus) used for conjugation to transfer DNA from one bacterium to anotherGenes coding for F-pilus are on F plasmid

  • Procaryotes: reproductionReproductionFission instead of mitosisChromosomal DNA replicationCytokinesisformation of divisome (several proteins that tag the centre of cell)Cell wall peptidoglycan depositedChromosomes separated

  • Eucaryotic cellsDiversityProtista: free-living marine unicellular, some photosynthetice.g. Giardia lamblia, dinoflagellates, Paramecium, PlasmodiumMulticellular organismsFungi, Plants, AnimalsDifferentiationModel organisms (a) Saccharomyces cerevisiae (yeast) (b) Arabidopsis thaliana (c) Caenorhabditis elegans (d) Drosophila melanogaster (e) Mus musculus

  • Eucaryotic cells StructureCharacteristics:Typically 10-30 umSeparation of DNA and cytoplasm by nuclear envelopePresence of membrane-bound compartments with specialized functions: Mitochondria, chloroplasts, ER, Golgi complexHighly specialized motor proteinsNuclear envelope and internal membranesOriginated from cell membrane differentiated and acquired special functions

  • Eucaryotic cellsorganelles can be divided into four categoriesThe nucleus and ribosomesendomembrane system energy-related organellescytoskeleton

  • Can you meet these objectives?Describe the cell theoryDescribe the basic properties of cellsOutline the major advances leading to modern cell biologyDescribe the properties of procaryotic cellsContrast and compare prokaryotes and eukaryotesDiscuss the cellular structure of prokaryotes