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A Tour of the Cell We study cells using microscopes and biochemistry.Cells come in a range of sizes (where light microscopes cannot magnify as well as electron microscopes) Microscopy --- Light microscope vs. electron microscope--Light: visible light passes through specimen. Refracts light so specimen is magnified. Magnifies up to 1000X. specimen can be alive/moving. Color. --Electron: focuses a beam of electrons through/onto specimen. Magnify up to 1,000,000 times. Specimen is non-living and in vacuum. Black and white.--transmission electron microscopy (TEM): 2D. creates a flat image with extreme detail. enhance contrast by staining atoms with heavy metal dyes.--scanning electron microscopy (SEM): 3D. used for detailed study of surface of a specimen. Gives great depth of field. Studying cell structure and function:1. Cell fractionation – take apart cells, separate major organelles.2. Ultracentrifuge – applies force 1 million times the force of gravity to further separate the cell organelles with the most dense at the bottom. 2 types of cells:1. prokaryotes: domain bacteria and archeaa. no nucleusb. DNA in nucleoidc. Cytosold. No organelles other than ribosomese. Small sizef. Primitiveg. Ex: bacteria and archea2. eukaryotes: domain eukarya (protists, fungi, plants, animals)a. has nucleus and nuclear envelopeb. cytosolc. membrane-bound organelles with specialized structure/functiond. much larger in sizee. ex: plant/animal cells Cell size and scale-cells must be small to maintain a large surface to volume ratio à large SA allows increased rates of chemical exchange between cell and environment-ex: small intestine has a highly folded surface to increase absorption of nutrients (with villi on the SI wall, and microvilli on each cell)-ex: root hairs in plants increase SA for increasing absorption of water and minerals. ORGANELLESNucleus:-control center of the cell-contains DNA-surrounded by double membrane (nuclear envelope), continuous with the rough ER-nuclear pores – controls what enters/leaves the nucleus-chromatin – complex of DNA + proteins, makes up chromosomes-nucleolus – subdomain of nucleus, assembles ribosomal subunits Ribosomes: -functions in protein synthesis -composed of rRNA + protein -large subunit + small subunit -types: free ribosomes and bound ribosomes free – float in cytosol, produce proteins used within the cell bound – attached to ER, make proteins for export from the cell Endomembrane system: regulates protein traffic and performs metabolic functions Endoplasmic Reticulum (ER): -network of membranes and sacs -types:rough ER (RER) – ribosomes on surface. Functions to package proteins for secretion, sends transport vesicles to Golgi, makes replacement membranesmooth ER (SER) – no ribosomes on surface. Functions to synthesize lipids, metabolize carbs, detox drugs and poisons, stores Ca2+ Golgi Apparatus:-function – synthesis and packaging of materials (small molecules) for transport in vesicles. Produces lysosomes. -series of flattened membrane sacs (cisternae) -cis face: receives vesicles -trans face: ships vesicles Lysosomes:-function – intracellular digestion. Recycle cell materials. Programmed cell death (apoptosis) -contains hydrolytic enzymes Vacuoles: -function – store materials (food, water, minerals, pigments, poisons) -membrane-bound vesicles -ex: food vacuoles, contractile vacuoles -plants have a large central vacuole to store water and ionsMitochondria: -function – site of cellular respiration -double membrane: outer and inner membranes-cristae: folds of inner membrane, contains enzymes for ATP production, increases surface area to increase ATP made -matrix: fluid-filled inner compartment Chloroplasts: -function – site of photosynthesis -double membrane -thylakoid disks in stacks (grana), stroma (fluid) -contains chlorophylls (pigments) for capturing sunlight energy Endosymbiont Theory-mitochondria and chloroplasts share similar origin-prokaryotic cells engulfed by ancestors of eukaryotic cells-evidence: double membrane structure, have own ribosomes and DNA, reproduce independently within cell Peroxisomes: -function – breakdown fatty acids, detox alcohol -involves the production of hydrogen peroxide Cytoskeleton: -function – support, motility, regulate biochemical activities -3 types of cytoskeletal fibers:--microtubules: protein = tubulin. Largest fibers. Shape/support the cell (compression resisting girders). Track for organelle movement. Forms spindle for mitosis/meiosis (chromosome movement). Component of cilia/flagella (cell motility).--microfiliments: protein = actin. Smallest fibers. Support cell on smaller scale (tension bearing elements). Cell movement. Ex: ameboid movement, cytoplasmic streaming, muscle cell contraction.--intermediate filaments: intermediate size. Permanent fixtures, maintain shape of cell. Fix position of organelles. Centrosomes: -region from which microtubules grow -also called microtubule organizer -animal cells have centrioles Cilia and Flagella: -flagella: long and few. Propel through water -cilia: short and numerous. Locomotion or move fluids -made of microtubules Extracellular matrix (ECM) (animal cells): -outside plasma membrane -composed of glycoproteins (ex: collagen) -function – strengthens tissues and transmits external signals to cell Intercellular junctions (animal cells): -tight junctions: 2 cells are fused to form a watertight seal -desmosomes: rivets that fasten cells into strong sheets -gap junctions: channels through which ions, sugar, small molecules can pass Cell wall (plant cells): -protect plant -composed of cellulose Plasmodesmata (plant cells): -channels between cells to allow passage of molecules PLANT CELLS ONLY: central vacuoles, chloroplasts, cell wall of cellulose, plasmodesmata ANIMAL CELLS ONLY: lysosomes, centrioles, flagella/cilia, desmosomes/tight junctions/gap junctions, extracellular matrix
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