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7.2: THE PLASMA MEMBRANE

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7.2: THE PLASMA MEMBRANE

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    1. 7.2: THE PLASMA MEMBRANE Membranes = “the edge of life”

    2. What must a membrane do? let some things leave / enter cell keep stuff inside or outside of cell be flexible as cell changes shape

    3. The cell membrane is composed of molecules called PHOSPHOLIPIDS.

    4. one end is strongly nonpolar (hydrophobic); one end is extremely polar (hydrophilic)

    5. the nonpolar lipid “tails” are repelled by polar water molecules; the polar “heads” of the molecules form hydrogen bonds with water molecules.

    6. So, every phospholipid molecule orients so that its polar “head” faces water and its nonpolar “tails” face away... two layers are formed with the tails facing each other...the result is called a LIPID BILAYER.

    7. Lipid bilayer membranes are: PERMEABLE to: lipids nonpolar molecules: O2, CO2 small polar molecules: H2O IMPERMEABLE to: ions (Na+, K+, Cl-) large polar molecules: sugars, proteins

    8. 3 Main Types of Membrane PROTEINS… Channels Receptor proteins Cell surface markers

    9. 1. CHANNELS: a channel will transport only certain kinds of molecules...which gives the cell membrane its selectively permeable nature

    10. 2. RECEPTOR PROTEINS: collect & transmit information from the cell’s environment

    12. 3. CELL SURFACE MARKERS: identify your body‘s cells as belonging to you (useful in cell-cell recognition)

    13. NUCLEUS contains the cell’s DNA contains all of the information for cell to function

    14. NUCLEAR ENVELOPE double membrane which encloses the nucleus

    15. CHROMATIN threadlike complex of DNA which makes up chromosomes in eukaryotic cells

    16. CHROMOSOMES compacted, coiled up chromatin; human cells have 46 chromosomes (23 pairs)

    17. NUCLEOLUS spherical region in the nucleus -synthesizes ribosomes

    18. RIBOSOME site of protein synthesis made in the nucleolus may be free (in cytoplasm) or attached to the ER

    19. The Endomembrane System **all structures are essentially compartments, closed off by their membranes from the cytoplasm

    20. ENDOPLASMIC RETICULUM (ER): extensive network used to transport and/or modify proteins; can be ROUGH (ribosomes) or SMOOTH (no ribosomes)

    21. Rough ER: rough appearance due to ribosomes on outer surface; manufactures and transports proteins.

    22. Smooth ER: synthesizes lipids, phospholipids, steroids detoxifies drugs and poisons

    23. GOLGI APPARATUS: stacked, flattened membranes finishes, sorts and ships many cell products (a.k.a. the “post office” of the cell)

    25. LYSOSOMES contain enzymes that digest macromolecules; recycle the cell’s own organic material; can destroy cells.

    27. Other Membrane-Bound Organelles:

    28. VACUOLE: used for storage; in animal cells, vacuoles are smaller than in plant cells

    29. PLANT VACUOLES… may contain soluble pigments in some cells (red and blue pigments in flowers);

    30. PLANT VACUOLES… help protect from predators by storing waste products that may also be poisonous compounds

    31. MITOCHONDRIA: sites of cellular respiration the # in cells varies and is related to the cell’s metabolic activity

    32. CHLOROPLASTS: (“the organelles that feed the world”) contain chlorophyll; site of photosynthesis (convert light energy into chemical energy

    33. MICROTUBULES & MICROFILAMENTS make up the cytoskeleton structural support to cell; maintain shape involved in cell movement

    35. Microfilaments: thin, solid protein fibers; stabilize cell shape

    36. Microtubules: thin, hollow cylinders made of protein can serve as “tracks” to guide organelle movement; involved in separation of chromosomes in cell division; make up CENTRIOLES

    38. FLAGELLA and CILIA: FLAGELLA: longer usually single extensions; used to propel a cell CILIA: shorter and more numerous than flagella; wavelike motion used to sweep extracellular material over/away from cell

    39. Extracellular Structures: CELL WALL: semirigid structure outside of cell membrane of PLANT CELLS; consists of CELLULOSE fibers; provides support, limits cell’s volume, and protects against fungi and/or microorganism infection.

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