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Transcript
Chapter 2 The Cell: the Basic Unit of Life Contents 1 2 3 Cells Cell Organization Two Fundamental Cell Types Cells Basic unit of living organism First named by Robert Hook in the 17th century Different types but the same essential properties Same building blocks: proteins, carbohydrates, fats, and nucleic acids Liver Neutrophil Goldfish skin Neuron Essential Functions of Living Cells 1 Growth Metabolism • Catabolism: breaking down large molecules to generate building blocks and energy • Anabolism: Generation of large molecules using building blocks and energy Essential Functions of Living Cells 2 Reproduction Cell cycle • Cyclical process of cell growth and division • Daughter cell must receive a correct copy of genetic material DNA replication before cell division Cell cycle Essential Functions of Living Cells 3 Maintenance of internal environments Use energy to maintain the internal environments • Unique molecules – Specific proteins, DNA etc. • Molecules also exit outside but with different concentrations – Water, salts, sugar etc. Amoeba Essential Functions of Living Cells 4 Response to external environments Sense a change in their environment Respond • Maintaining osmotic homeostasis • Bacterial chemotaxis • Release of digestive enzymes from stomach cells • ….. Essential Functions of Living Cells 5 Communication with each other Between cells in an organism • e.g. Nerve cell and muscle Between single cell organisms • e.g. Mating of yeast cells, quorum sensing of bacteria Essential Functions of Living Cells 6 Differentiation in multicellular organisms Cells differentiate to cells with specific functions Specific cells organize into different tissues and organs Common Cellular Processes Constant supply of energy Need energy for all the cellular activities Energy source • Sun: photosynthetic plant or bacteria • Food and Chemicals Chemical reactions Enzymes: protein catalyst accelerating chemical reactions Common Cellular Processes Cell processes occur in a series of small steps Pathway: a process consisting of a series of steps Regulation of processes Regulation of various processes by regulation of protein-protein and protein-DNA interactions Cell cycle, blood sugar levels, blood pressure, body water balance etc. Cell Organization Interaction of molecules with water Important factor for determining the molecular organization within a cell Hydrophilic (water soluble) or Hydrophobic (water insoluble) • Congregation of hydrophilic parts with other hydrophilic parts • Congregation of hydrophobic parts with other hydrophobic parts Binding of molecules Specificity of molecular bindings determines cellular processes Binding: fitting between molecules • Depends on shape and chemical properties (charge) Cellular Membranes I Provide structural organization Lipid bilayer with hydrophobic core and hydrophilic face Plasma (cell) membrane: Hydrophobic barrier between inside (cytoplasm) and outside of the cell Internal membranes • • • • Nucleus Endoplasmic reticulum, Golgi apparatus Mitochondria Chloroplast Cellular Membranes II Control molecular transport across the membrane Free diffusion • Small, electrically neutral or slightly charged molecules (CO2, O2, water) Transport through membrane-bound channels and transporters Two Fundamental Cell Types Prokaryotic cells Prokaryote (pro; before, karyon: kernel or nucleus) No nuclear membrane Small (0.2-2 m), mostly single-celled organisms • Eubacteria : common bacteria, e.g. E.coli, blue-green algae • Archaea (Archaebacteria) Eukaryotic cells Eukaryote (well-formed nucleus) Nuclear and internal membranes organelles Larger than prokaryotes (10-100 m) • Single-celled: yeast, green algae, amoebae • Multicellular: fungi, plant, animal The Scale of Life The phylogenetic tree of life as defined by comparative ribosomal RNA sequencing Two Fundamental Cell Types Procaryote & Eucaryote Primary Difference: presence or absence of nucleus (more details in Table 2.1 and 2.2) Procaryotic Cells Procaryote (pro; before, karyon: kernel or nucleus) No nuclear membrane Small (0.5-3 m), mostly single-celled organisms Eubacteria : common bacteria (e.g. E. coli, blue-green algae ) Archaea (Archaebacteria): methanogens (methane-producing), thermoacidophiles, and halobacteria (high salt) • Live in extreme environments. • Possess unusual metabolism. Eubacteria Divided into two groups by gram stain. Gram-negative cell (e.g. E. coli) • • • • Outer membrane Peptidoglycan Cytoplasmic (inner) membrane Periplasm – Between inner and outer membranes Gram-positive cell (e.g. Bacillus subtilis) • • • • No outer membrane Peptidoglycan Teichoic acid Cytoplasmic membrane 21 22 23 Teichoic acids Teichoic acids (cf. Greek τειχος, teichos, "wall") are bacterial polysaccharides[1] of glycerol phosphate or ribitol phosphate linked via phosphodiester bonds They can be covalently linked to Nacetylmuramic acid of the peptidoglycan layer, to the lipids of the cytoplasmic membrane, or to a terminal D-alanine in the tetrapeptide crosslinkage between N-acetylmuramic acid units. Cellular Membranes Provide structural organization Lipid bilayer with hydrophobic core and hydrophilic face Plasma (cell) membrane: Hydrophobic barrier between inside (cytoplasm) and outside of the cell Internal membranes for eucaryote • • • • Nucleus Endoplasmic reticulum, Golgi apparatus Mitochondria Chloroplast Cytoskeleton and Centrioles Viruses No independent reproduction Genetic material (DNA or RNA) Proteins (Capsid) Host specificity Bacteria (bacteriophages), human etc Tissue specificity Microbial Diversity psychrophile: optimum temp < 20oC mesophile: 20oC < optimum temp < 50oC thermophile: 50oC < optimum temp aerobic: growth in the presence of oxygen anaerobic: growth without oxygen facultative: growth under either circumstances coccus: spherical or elliptical bacillus: cylindrical or rod spirillum: spiral Naming Cells Escherichia coli (E. coli) written in italic Escherichia: genus coli: species various strains of E. coli --- (ex) E. coli K12 Viruses Not cells No independent reproduction (not alive by itself) • Genetic material (DNA or RNA) • Proteins (Capsid) “Viruses are in the semantic fog between life and non-life.” (Campbell and Reece, Biology, 6e, p 339.) Are viruses living beings? “The answer to that question is ‘no’, inasmuch as viruses are incapable of independent life.” (de Duve, Life Evolving, p.313) Conclusion: Viruses do not fit the basic definition of cellular life. • Require host for all cellular activities • No metabolic capability of their own Bacteriophage Bacteriophage: virus infecting bacteria lytic cycle: reproduction of virus (Fig. 2.1) lysogenic cycle: Phage DNA is incorporated into the host DNA Eucaryote Eucaryotic cells Eukaryote (well-formed nucleus) Larger than procaryotes (10-100 m) • Single-celled: yeast, green algae, amoebae • Multicellular: fungi, plant, animal Nuclear and internal membranes organelles • • • • Nucleus --- contains chromosomes as nuclear material Mitochondria --- powerhouse of a cell Golgi body --- responsible for the secretion of certain proteins Vacuole --- responsible for food digestion, osmotic regulation, and waste-product storage • Chloroplast --- responsible for photosynthesis • endoplasmic reticulum, lysosome, glyoxysome …. Nucleus and Mitochondria Endoplasmic Reticulum Cell Cycle in a Eucaryote Cell Cycle (Fig. 2.4) S phase: --- DNA synthesis M phase: --- mitosis G 1, G 2 : --- G strands for gap between S and M phase --- Cell growth Mitosis DNA replication Mitosis Prophase • Condensation of chromosomes and disappearance of nuclear membrane Metaphase • Alignment of chromosome in the center • Pulling by spindle fibers attached to the kinetochore Anaphase • Splitting of chromatids and pulling to the opposite ends of the cell Telophase • Decondensation of chromosome • Formation of new nuclear membrane Cytokinesis Cell division after mitosis Interphase The time between cell division and the next mitosis (G1, S, G2) Mitosis and Cytokinesis Chromosome Tightly packed complex of DNA and histone proteins Eucaryotic Cells Fungi Yeasts --- single small cells of 5- to 10-m size Molds --- filamentous fungi, have a mycelial structure Algae Unicelluar algae (microalgae) --- 10 to 30 m Plantlike multicelluar algae Protozoa Unicellular, motile, relatively large (1 - 50 mm) --- amoeba Plant cells Animal cells http://multimedia.mcb.harvard.edu/anim_innerlif e_hi.html