The Plasma Membrane 3'4

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The Plasma Membrane (3.4)

• The lipid bilayer is not solid and rigid, but
  somewhat fluid.
• Cell membranes are of mixed composition of
• proteins, which can be
• embedded in the bilayer or
• at the inner or outer surface, and
• 2) various lipids including
• Phospholipids
• Glycolipids
• Cholesterol

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Fluid Mosaic Model

• Phospholipids and Proteins
• Phospholipids impart fluidity
• Proteins carry out most functions
• Transport proteins
• Adhesion proteins
• Receptor proteins
• Recognition proteins

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Proteins (pg. 47)

• Enzymes some proteins are enzymes that serve in
  a cells metabolic processes
• Transport proteins allow water-soluble
  substances to move through the membrane by
  binding to the molecules or ions and moving them
  into or out of the cell
• Receptor proteins bind extracellular substances
  that trigger changes in a cells activities. Ex.
  hormones
• Recognition proteins identify a cell type
• Adhesion proteins help cells of the same type
  stick together and stay positioned in their
  tissues

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cytoskeletal protein)
ADHESION PROTEIN
open channel
gated channels (open and closed)
active transport
LIPTD BILAYER
RECEPTOR PROTEIN
RECOGNITION PROTEIN
TRANSPORT PROTEINS
Look closely at each type of molecule although
they look the same, they have distinct features
Fig. 3.11, p. 47
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The Cytomembrane System (3.5, pg. 48)

• The CS
• A series of organelles in which lipids are
  assembled and polypeptide chains are modified
  into final proteins
• Includes the ER, Golgi bodies, and various
  vesicles. These organelles functionally connect
  with one another
• The products of the cytomembrane system (CS) are
  sorted and shipped to different destinations

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Endoplasmic Reticulum

• The function of the CS begins with the ER
• The ER is continuous with the cell membrane,
  curves throughout the cytoplasm, and encloses the
  nucleus (can be smooth or rough)
• Rough ER is arranged into stacks of flattened
  sacs with many ribosomes attached
• Every new polypeptide chain is made on a
  ribosome, but only those with a built-in signal
  can enter the rough ER
• Once inside, enzymes may attach oligosaccharides
  and other side chains to the polypeptide

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ER-continued

• Many specialized cells secrete final proteins,
  these cells have a lot of rough ER
• Ex.-pancreas, ER-rich gland cells make and
  secrete enzymes for digestion
• Smooth ER has no ribosomes and is like connecting
  pipes
• Many cells assemble most of their lipids inside
  these pipes
• Ex. liver cells-smooth ER inactivates certain
  drugs and harmful by-products of metabolism
  skeletal muscle cells-store and release calcium
  ions essential for muscle contraction

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Golgi bodies

• Look like a stack of pancakes, flattened sacs
• In Golgi bodies, enzymes finish proteins and
  lipids, sort them, and package them inside
  vesicles for shipment (gift wrap dept.-it may
  attach a phosphate group which is like a mailing
  tag)
• The vesicles bulge out from the top layer and
  break away into the cytoplasm

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Vesicles (pg. 49)

• Tiny membranous sacs that move through the
  cytoplasm
• Ex.-1) lysosome-contains enzymes to digest
  organic compounds, including whole cells
  (bacteria)
• 2) peroxisomes-contain enzymes that break down
  fatty acids and amino acids

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The Cytomembrane Systemsee pg.48
Vesicles
Golgi body
Secretory pathway
Smooth ER
Rough ER
Nucleus
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Moving substances by diffusion and osmosis (3.6)

• Both sides of the cell membrane are mostly water,
  with lots of dissolved substances, this is a
  solution (when one substance is dissolved in
  another)
• 2 parts to a solution
• Solvent-the substance doing the dissolving
• Solute-the substance being dissolved

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Diffusion

• Movement of substance from a region where it is
  more concentrated to one where it is less
  concentrated

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Solutions

• Concentration-how much is water? How much is
  stuff
• Gradient-the number of molecules in one region is
  not the same as another region
• Concentration gradient-the difference in the
  number of molecules or ions of a given substance
  in two adjoining regions

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Concentration gradient

• Molecules move because of random movement, the
  natural energy of molecules
• They are in constant motion and collide randomly
• Where there are more molecules, there are more
  collisions
• Each molecule diffuses according to its own
  concentration gradient
• Once equilibrium is reached, they move back and
  forth at equal rates (but they never stop moving)

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Factors Influencing the Rate and Direction of
Diffusion

• Concentration gradient
• Until equilibrium is reached
• Molecular size
• Small molecules move faster
• Temperature
• Faster at higher temperatures
• Electric or Pressure gradient
• Electrical charge difference
• Pressure differences

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Directional Movement of Water Across Membranes

• Osmosis
• Diffusion of water due to a water concentration
  gradient between two regions that are separated
  by a selectively permeable membrane
• Osmotic movement
• Dependent on concentration of solutes in the
  water
• Side with more solutes has a lower
  concentration of water
• remember the solution is 100, more water means
  less stuff and vice versa

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Osmosis and Tonicity

• Hypotonic
• Water diffuses in
• Cell swells
• Hypertonic
• Water diffuses out
• Cell shrinks
• Isotonic
• No net change
• These prefixes refer to the stuff