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Transcript
Cells: Chapt. 4 Two Basic Types of Cells • Prokaryotes: – prounounced: pro-carry-oats • Eukaryotes – Proun: you-carry-oats A. Prokaryotes Small, simple cells (relative to eukaryotes) Size: about 1 µm (1 micron) No internal membrane-bounded organelles No nucleus Simple cell division Contain the; 1. true bacteria & 2. archaebacteria 1. True Bacteria = Eubacteria • Majority of bacteria • Examples include: E. coli, Lactobacillus (yoghurt), Lyme disease Eubacteria •Peptidoglycan cell walls (carbos & AA) •Separated into Gram + and - forms Text pg. 58 Bacteria in the Environment example: Iron utilizing Baceria A B A) An acid hot spring in Yellowstone is rich in iron and sulfur. B) A black smoker chimney in the deep sea emits iron sulfides at very high temperatures (270 to 380 degrees C). 2. Archaebacteria • Live in extreme environments: high salt, high temps • Different cell wall • Very different membrane lipids • Unusual nucleic acid sequence Archaea types: Based on their physiology, Archae can be organized into three types: • • • Methanogens (prokaryotes that produce methane); Extreme halophiles (prokaryotes that live at very high concentrations of salt (NaCl); Extreme (hyper) thermophiles (prokaryotes that live at very high temperatures). All archaea have features that distinguish them from Bacteria (i.e., no murein in cell wall, ether-linked membrane lipids, etc.). And, these prokaryotes exhibit unique structural or biochemical attributes which adapt them to their particular habitats. B. Eukaryotes • Bigger cells: 10-100 µm • True nucleus • Membrane-bounded structures inside. Called organelles • Divide by a complex, well-organized mitotic process Liver Cell 9,400x Eukaryotes • Larger more complex cells that make up most familiar life forms: plants, animals, fungi, algae • Surrounded by a cell membrane made of lipids • Text pg 60-61 The Cell Theory • Cells first observed by R. Hooke 1665 • Named for the Monk prayer cells • Cell Theory states that; 1. All life is composed of cells 2. Cells are the basic units of life 3. Cells arise from already existing cells Cells are typically Small Typical cell size •Text pg. 56 Why are Cells Small? • Cells must exchange gases & other molecules with environment… • Nutrients in, Wastes out • As size increases, the rate of diffusion exchange slows down…. • This is due to the ratio of surface area to volume Surface Area to Volume • Cell surface area is important in taking in nutrients • Sfc area increases as the square of cell diameter • But… entire cell volume needs to be fed • And, cell volume increases as the cube of cell diameter Consider 2 Cells... Surface Area to Volume Cell Radius (R) 5 µm 50 µm Surface Area (4πr2) Volume 3 (4/3πr ) Surface Area to Volume Ratio 314 µm2 31,400 µm2 3 524 µm3 524,000 µm 0.6 0.06 The Eukaryotic Cell: Components • Outer cell membrane composed of lipids and proteins • Cytoplasm: interior region. Composed of water & dissolved chemicals…a gel • Numerous organelles…. Organelles • Specialized structures within eukaryotic cells that perform different functions... • Analogous to small plastic bags within a larger plastic bag. • Perform functions such as : – protein production (insulin, lactase…) – Carbohydrates, lipids… • Text pg 60-61 Organelles of Note: The Nucleus • Contains the genetic material (DNA), controls protein synthesis. DNA --> RNA --> Protein • Surrounded by a double membrane with pores • Contains the chromosomes = fibers of coiled DNA & protein • Text pg. 62 Chromosomes All Chromosomes from a single cell One chromosome Pulled apart A single chromosome Showing the amount of DNA within Mitochondria • Generate cellular energy in the form of ATP molecules • ATP is generated by the systematic breakdown of glucose = cell respiration • Also, surrounded by 2 membrane layers • Contain their own DNA! • A typical liver cell may have 1,700 mitoch. • All your mitoch. come from your mother.. • Text pg. 68 Chloroplasts • Found in plants, algae and some bacteria. Responsible for capturing sunlight and converting it to food = photosynthesis. • Surrounded by 2 membranes • And…contain DNA • Text pg. 69 Ribosomes • Size ~20nm • Made of two subunits (large and small) • Composed of RNA and over 30 proteins • Come in two sizes…80S and 70S • S units = Sedimentation speed Ribosomes • DNA --> RNA --> Protein • The RNA to Protein step (termed translation) is done on cytoplasmic protein/RNA particles termed ribosomes. • Contain the protein synthesis machinery • Ribosomes bind to RNA and produce protein. Endoplasmic Reticulum = ER • Cytoplasm is packed w. membrane system which move molecules about the cell and to outside • An internal cellular subway system • Outer sfc of ER may be smooth (SER) • Or Rough (RER) • ER functions in lipid and protein synthesis and transport Golgi Complex • Stacks of membranes… • Involved in modifying proteins and lipids into final form… – Adds the sugars to make glyco-proteins and glyco-lipids • Also, makes vesicles to release stuff from cell • Text pg. 66-67 ER to Golgi network Lysosomes • important in breaking down bacteria and old cell components • contains many digestive enzymes • The ‘garbage disposal’ or ‘recycling unit’ of a cell • Malfunctioning lysosomes result in some diseases (Tay-Sachs disease) • Or may self-destruct cell such as in asbestosis • Text pg 67 Cytoskeleton • Composed of 3 filamentous proteins: Microtubules Microfilaments Intermediate filaments • All produce a complex network of structural fibers within cell • Text pgs. 72-76 The specimen is human lung cell double-stained to expose microtubules and actin microfilaments using a mixture of FITC and rhodamine-phalloidin. Photo taken with an Olympus microscope. Microtubules • Universal in eukaryotes • Involved in cell shape, mitosis, flagellar movement, organelle movement • Long, rigid, hollow tubes ~25nm wide • Composed of a and ß tubulin (small globular proteins) • Text pg. 72 http://www.cytochemistry.net/Cell-biology/ Microfilaments • Thin filaments (7nm diam.) made of the globular protein actin. • Actin filaments form a helical structure • Involved in cell movement (contraction, crawling, cell extensions) • Text pg. 72 Intermediate filaments • Fibers ~10nm diam. • Very stable, heterogeneous group • Examples: Lamins: hold nucleus shape Keratin: in epithelial cells Vimentin: gives structure to connective tissue Neurofilaments: in nerve cells Text pg. 72 Image of Lamins which reside in the nucleus just under the nuclear envelope Cell Motility: Flagella & Cilia • Both cilia & flagella are constructed the same • In cross section: 9+2 arrangement of microtubules (MT) • MTs slide against each other to produce movement • Text p 74 Human Sperm: TOTO-3 iodide for DNA (blue) and Nile red for membrane lipid (red) How Flagella Move a Cell Possible Origins of Eukaryotic Cells • Text pg 70 Infolding of outer membranes Uptake of prokaryotes Endosymbiosis • Theory that eukaryotic cells arose from an early prokaryote (1) engulfing a second, smaller prokaryote (2) • The internalized #2 was not digested but became a symbiote. • Today’s mitochondria & chloroplasts may have arisen this way • Text pg. 70 Evidence for Endosymbiosis • Double membrane around both organelles • Both organelles have their own DNA • Both organelles have smaller (70S) ribosomes… • Both organelles divide by simple fission