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Lecture #2 Date _________

Lecture #2 Date _________. A Tour of the Cell. Microscopes. Micrograph = a picture of an image seen through a microscope. Compound Light Microscope 2 or more glass lenses bent light from specimen to form enlarged image Specimen must be small or thin enough Stains may alter or kill cells.

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Lecture #2 Date _________

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  1. Lecture #2 Date _________ A Tour of the Cell

  2. Microscopes • Micrograph = a picture of an image seen through a microscope

  3. Compound Light Microscope 2 or more glass lenses bent light from specimen to form enlarged image Specimen must be small or thin enough Stains may alter or kill cells Electron Microscopes Electrons accelerated to wavelengths shorter than those of light Magnetic field bends electrons Better resolution of fine details Transmission EM: magnetic field is “lens”; electrons through specimen, focused, and magnified Scanning EM: thin coat of metal on specimen; electrons move back and forth across specimen; detector transforms energy into image Microscopes

  4. Cell • The smallest unit that retains the properties of life

  5. Cell size • As cell size increases, the surface area to volume ratio decreases • Volume increases by cube of diameter, but surface area only increases by square! • A.k.a. If a cell grows, its volume increases more rapidly that its surface area! • Rates of chemical exchange may then be inadequate • Each part of membrane must serve 4 times as much cytoplasm! (Not as efficient!) • Folding increases surface area!

  6. All Cells Have • Plasma Membrane • Outermost membrane • Separates cell from environment • Selectively permeable • Nucleus or Nucleiod • DNA occupies a membranous sac or an interior region • Cytoplasm • Semifluid matrix • Contains ribosomes (where proteins are built)

  7. Prokaryotic Cells No nucleus No membrane-bound organelles Naked circular DNA, ribosomes, sometimes a cell wall (peptidoglycans) Ex: bacteria Domains: Archae and Bacteria Kingdoms: Archaebacteria and Eubacteria Eukaryotic Cells Contain a nucleus Have membrane-bound organelles Ex: algae, trees, YOU Domain: Eukarya Kingdoms: Protist, Fungi, Plant, Animal Sometimes you feel like a nut!

  8. Cell Membranes • Plasma Membrane surrounds cell • A barrier • Selectively Permeable • Organelles have membranes • Subdivide cytoplasm = keep reactions separate! • Phospholipid Bilayer • two layers of lipids • Surface Proteins • Carry out membrane functions • Channels, pumps, receptors

  9. Fluid Mosaic Model of the Cell

  10. Eukaryotic Cells • Contain Organelles • Internal, membrane-bound sac or compartment that serves one or more specialized functions in eukaryotic cells • Ex: nucleus, ER, Golgi body, vesicles, mitochondria • Non-membranous Structures • Ex: ribosomes and cytoskeleton

  11. Why Organelles? • Compartmentalization allows a large number of activities to occur simultaneously in a small space! • The cell can synthesize and break down materials at the same time! • Molecules can be made, stored, and used later!

  12. Plant Cells Central Vacuole Chloroplasts Cell Wall Animal Cells NO cell wall or chloroplasts Lysosomes Centrioles Organelles Structures in common? Because there are functions that ALL cells need!

  13. Nucleus • “Protective container” for DNA – (instructions for building proteins) • Keeps DNA away from metabolic machinery of cytoplasm • Outer membrane is boundary where cells can control passage and signals to and from cytoplasm

  14. Nucleus • Nuclear Envelope • Double-membrane system (2 outer membranes) • Lipid Bilayer controls what goes in and out (pores) • Protein filaments on inner surface anchor DNA • Ribosomes on outside surface • Nucleoplasm • Nucleolus • RNA made (subunits for ribosomes) • Chromosomes = one DNA molecule plus associated proteins • Chromatin = cell’s collection of DNA plus associated proteins

  15. Nucleus • Genetic material... •chromatin •chromosomes •nucleolus: rRNA; ribosome synthesis • Double membrane envelope with pores • Protein synthesis (mRNA)

  16. Cytomembrane System • A series of organelles in which lipids are assembled and new polypeptide chains are modified into final proteins • Endoplasmic Reticulum • Golgi Bodies • Vesicles

  17. Endoplasmic Reticulum • Structure: stacks of flattened stacks • Continuous with nuclear envelope in animals • Rough ER vs. Smooth ER • Some polypeptide chains enter the space in RER and get modified • In the membrane of SER, lipids are assembled from building blocks delivered earlier • Vesicles bud from the ER membrane and transport unfinished lipids and proteins to a Golgi body

  18. Endomembrane system, I • Endoplasmic reticulum (ER) • Continuous with nuclear envelope • Smooth ER •no ribosomes; •synthesis of lipids, •metabolism of carbohydrates; •detoxification of drugs and poisons • Rough ER •with ribosomes; •synthesis of secretory proteins (glycoproteins), membrane production

  19. Ribosomes • Protein manufacture • Free •cytosol; •protein function in cell • Bound •endoplasmic reticulum; •membranes, organelles, and export

  20. Golgi Body • Structure: series of flattened membrane-bound stacks • Proteins and lipids take on their final form • “Finishing touches” put on proteins and lipids; then sorted and packaged inside vesicles for shipment (vesicles form as patches of membrane bulge out break away into the cytoplasm)

  21. Endomembrane system, II • Golgi apparatus •ER products are modified, stored, and then shipped • Cisternae: flattened membranous sacs • trans face (shipping) & cis face (receiving) • Transport vesicles

  22. Vesicles • Tiny, membranous sacs that move through cytoplasm or take position in it • Lysosomes • Peroxisomes

  23. Lysosomes • Animal cells and certain fungal cells • Intracellular digestion • Enzymes for breakdown of waste, etc.

  24. Peroxisomes • Single membrane • Produce hydrogen peroxide in cells • Metabolism of fatty acids and amino acids; detoxification of alcohol (liver) • Hydrogen peroxide then converted to water and oxygen

  25. Endomembrane system, III • Lysosomes •sac of hydrolytic enzymes; digestion of macromolecules • Tay-Sachs disease~ lipid-digestion disorder

  26. Mitochondria • Structure: double membrane system • Inner membrane folds back on itself (cristae) • Forms 2 distinct compartments • Resemble bacteria – size, DNA,ribosomes • Site of Cellular Respiration • Breaks down organic compounds into carbon dioxide and water in order to release energy (ATP) • requires oxygen

  27. Other membranous organelles, I • Mitochondria • quantity in cell correlated with metabolic activity; •cellular respiration; •double membranous (phospholipid); •cristae/matrix; •intermembrane space; •contain own DNA

  28. Plant Organelles • Chloroplasts • Plastids • Central Vacuole

  29. Plastids • Specialize in photosynthesis or storage • Chloroplasts convert sunlight energy into energy of ATP which is used to make sugars (photosynthesis) • Disk shape; stroma enclosed by 2 outer membrane layers; stroma contains thylakoid membrane (stacks = grana) • Resemble bacteria • Chromoplasts – contain carotenoids • Amyloplasts – lack pigments

  30. Other membranous organelles, II • Chloroplast •type of plastid; •double membranous; •thylakoids (flattened disks); •grana (stacked thylakoids); •stroma; •own DNA

  31. Central Vacuole • Fluid-filled • Stores amino acids, sugars, ions, and toxic wastes • Turgor pressure

  32. Cytoskeleton • Interconnected system of fibers, threads, and lattices between nucleus and plasma membrane • Gives internal organization, shape, and capacity to move

  33. The Cytoskeleton • Fibrous network in cytoplasm • Support, cell motility, biochemical regulation • Microtubules: •thickest; long, hollow cylinder •tubulin protein – monomers added •shape, support, transport, chromosome separation (cell division) • Microfilaments : •thinnest; 2 actin protein filaments twisted as helix; •motility, cell division, shape • Intermediate filaments: middle diameter; most stable; keratin; only in some animal tissues; used for shape

  34. Cell Motility • Microfilaments and Microtubules • Length of MF or MT can grow or diminish by assembly or disassembly of subunits. • Pseudopod • Parallel rows of MF or MT actively slide in specific directions. • Muscle cells • MF or MT shunt organelles or parts of cytoplasm from one place to another.

  35. Cilia/flagella • Locomotive appendages • “9+2 array” arises from a centriole •9 doublets of microtubules in a ring •2 single microtubules in center •connected by radial spokes •anchored by basal body •dynein protein – “motor”

  36. Centrosomes/centrioles • Centrosome: region near nucleus • Centrioles: 9 sets of triplet microtubules in a ring; used in cell replication; only in animal cells

  37. Cell Surface Specializations • Cell Wall • Outside plasma membrane • Cellulose • Protects and supports • Eukaryotes: plants, many protists, many fungi • Matrixes Between Animal Cells • Cell-to-Cell Junctions • Where cell sends and receives signals and materials

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