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Cell Architecture Classification of organisms “Five kingdom system:” Divide all organisms into groups (kingdoms)-different groups have different combinations of cell parts (organelles) ! Procaryota ! Animalia ! Plantae ! Fungi ! Protista Classification by molecular biology Modern systems divide organisms into groups-(domains, kingdoms)—on the basis of DNA sequences Prokaryotes ! Bacteria, Archaea ! Simplest structure (Protobionts: a step toward living cells?) Plasma Membrane Thin sheet 7-9 nm (0.007-0.009 !m) thick Composition: lipid (fat) and protein Found in all cells Functions: ! serves as platform for biochemical reactions ! recognizes outside stimuli ! controls transport of molecules (and larger things) into and out of cell. Cell Wall Thick net (variable width) surrounding the plasma membrane; rigid Found in most prokaryotes (bacteria, archaea); also plants, fungi, some protists Composition: peptidoglycan, cellulose, chitin, etc. (long molecules, porous net) Functions ! limits the size of cell ! controls cell growth Nucleoid Nucleic acid (long, stringy molecule) in center of cell Function: contains information (DNA) ! cell functions (metabolism) ! growth of cell ! reproduction Ribosomes Small, solid spheroids (0.02 !m diameter) Nucleic acid (RNA) and protein, two subunits each Ave. 30,000 per cell Function ! synthesis of proteins Eukaryotes ! Plants, Animals, Fungi, Protists ! Complex cell structures ! Multicellular organisms, with specialized cells Organelles in prokaryotes that are the "same" in eukaryotes Plasma membrane Cell wall (in plants, fungi, some protists) Ribosomes Nucleus (nuclei) Spheroid, 10-20 !m diameter Present in all eukaryotes: usually one per cell (more? coenocytic or syncitial) Surrounded by nuclear envelope Nucleolus: makes ribosomes Chromatin: ! Nucleosomes ! Chromosomes ! Centromeres ! Telomeres Function: like nucleoid of prokaryotes Mitochondrion (-dria) Spheroid ca. 1 !m diameter Surrounded by a double membrane Crista (-ae): inner membrane folds Matrix: liquid gel center Function: directs energy transformation, metabolism Found in all eukaryotic cells: 1 to 10,000 (ave. 100) per cell Mitochondria in cornial cells are long and tubular a and d and green in c and f is autofluorescence b and e and red in c and f is a fluorescent dye absorbed by mitochondria Plastid Spheroid 5 !m diameter Found in plants and some protists ! Double membrane ! Thylakoids ! Stroma Functions depend on type: ! Chloroplast (green) ! Leukoplast (white) ! Chromoplast (colored) ! Proplastids Organelles in prokaryotes and eukaryotes ! Plasma membrane ! Cell wall (in prokaryotes, plants, fungi, some protists) ! Ribosomes ! Nucleoid/nucleus ! Mitochondrion ! Plastids Endoplasmic reticulum (E.R.) (“network between organelles”) Interconnected flattened or tubular sacs, cisterna(e) Functions: synthesis and packaging ! Rough: proteins ! Smooth, cell wall carbohydrates, glycogen (starch), glycoproteins, steroid hormones. In all eukaryotic cells Golgi apparatus (dictyosome, in plants) Dense complex of cisternae, several per cell Functions: ! synthesis of carbohydrates on proteins (glycoproteins), ! transport of proteins to different compartments in cell Found in all eukarotic cells Vesicles Small sacs Single membrane Functions: ! storage, isolation ! transport Vacuoles Larger sacs Single membrane In protists, storage organs, digestive organs, related to water pumping (contractile vacuole) In plants and fungi, large storage organs salts, sugars, red and blue pigments in flowers, wastes, strange chemicals (poisons ) Cytoskeleton Microtubules Stiff helical rods of protein (tubulin); 25 nm diam Functions: ! Structural support (e.g. mammalian nerve cell). ! Support for movement (e.g., vesicles, cilia, flagella, spindles). Motor proteins: ! Kinesin toward + end ! Dynein toward - end Microfilaments Flexible rods of protein (actin); 7 nm thick Functions: ! Structural support ! Support for movement (e.g., muscles, streaming). Motor protein: ! Myosin Intermediate filaments Stiff protein rods, 8-12 nm thick Function: hold organelles in place Figure 4. IF-associated proteins provide flexible intracytoplasmic resilience in response to external stresses by reversibly cross-linking IFs to other cytoskeletal and membrane sites. (A through C) BPAG1n/dystonin, a 280-kD linker protein with actin- and neurofilament-binding domains, aligns neurofilaments along actin stress fibers when a cultured mammalian cell is triply transfected to express BPAG1n, NF-L, and NF-H. (A) Neurofilament; (B) BPAG1n/dystonin; (C) actin. [Reproduced with permission from Yang et al. (50).] (D) Electron micrograph of the residual cytoskeleton of a rat embryo fibroblast after dissolution of actin filaments with gelsolin. Linked to 10-nm gold particles, antibodies against the 500-kD cross-linker protein plectin reveal bridges between microtubules and IFs. Pseudocolored elements are microtubules (orange), IFs assembled from vimentin (green), plectin (red), and gold particles marking plectin (yellow). (E) Model suggesting that plectin mediates linking between IFs, microtubules, actin, myosin, and membrane-bound adhesion sites (focal contacts or plasma membrane components) (51, 53). (Images kindly provided by T.ハSvitkina and G.ハBorisy.) Dynamic relationships between membranous organelles ! E.R. formed by outbudding of nuclear envelope ! E.R. produces vesicles: substances produced in E.R. (e.g. proteins, tagged with carbohydrates; glycoproteins) appear in vesicles ! Golgi accepts materials from E.R. ! Golgi vesicles modify materials (e.g. altered glycogroups) ! Golgi vesicles can (a) stay as storage vesicles (e.g. lysosomes), (b) fuse with plasma membrane to secrete their substance, (c) fuse with another membrane (e.g. vacuolar membrane) to transfer material into an organelle. ! Secretion vesicles can be “constitutive” or “regulated”—Golgi targets different materials into each. Cells in various organisms Plants: have all the organelles described for eukaryotes (except some specialized cells) Fungi: like plant cells in number and type of organelles, but without plastids (also many other biochemical, structural, and behavioral differences) Animals: no cell wall, no plastids, no large vacuole Protists: +/- cell wall, pellicle, contractile vacuole Bacteria, archaea: +/- cell wall, no nucleus, mitochondria, plastids, E.R., Golgi; but cyanobacteria have thylakoids (like inside of plastids)