Cell Architecture

“Five kingdom system:” Divide all organisms into groups (kingdoms)--different groups have different combinations of cell parts (organelles) ! Procaryota ! Animalia ! Plantae ! Fungi ! Protista

Classification of organisms

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 plasmamembrane; rigid

Found in most prokaryotes (bacteria, archaea); alsoplants, 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: usuallyone per cell (more? coenocytic orsyncitial)

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 autofluorescenceb 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.) (“networkbetween 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 IFsto other cytoskeletal and membrane sites. (A through C) BPAG1n/dystonin, a 280-kD linker protein with actin- and neurofilament-bindingdomains, 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) Electronmicrograph of the residual cytoskeleton of a rat embryo fibroblast after dissolution of actin filaments with gelsolin. Linked to 10-nm goldparticles, antibodies against the 500-kD cross-linker protein plectin reveal bridges between microtubules and IFs. Pseudocolored elementsare microtubules (orange), IFs assembled from vimentin (green), plectin (red), and gold particles marking plectin (yellow). (E) Modelsuggesting that plectin mediates linking between IFs, microtubules, actin, myosin, and membrane-bound adhesion sites (focal contacts orplasma membrane components) (51, 53). (Images kindly provided by T.ﾊSvitkina and G.ﾊBorisy.)

Dynamic relationships between membranousorganelles

! E.R. formed by outbudding of nuclear envelope

! E.R. produces vesicles: substances producedin E.R. (e.g. proteins, tagged withcarbohydrates; glycoproteins) appear in vesicles

! Golgi accepts materials from E.R.

! Golgi vesicles modify materials (e.g. alteredglycogroups)

! Golgi vesicles can (a) stay as storage vesicles(e.g. lysosomes), (b) fuse with plasmamembrane to secrete their substance, (c) fusewith another membrane (e.g. vacuolarmembrane) to transfer material into anorganelle.

! Secretion vesicles can be “constitutive” or“regulated”—Golgi targets different materialsinto 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)