Membranes and Cellular Transport

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Membranes and Cellular Transport

• Chapter 5

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Phospholipid Bilayer

• Phospholipid has two fatty-acid chains attached
  to its backbone.
• One end (the lipid) is strongly non-polar while
  the other end (the phosphate) is strongly polar.
• polar head faces outward toward the water
• non-polar tails face inward away from the water.

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Cell Membrane Fluid Mosaic Model

• Cell membrane is called a Fluid Mosaic because
  the inside of the membrane is a fluid and the
  different structures (proteins) are floating
  (in what looks like random order, but not really)
  in the fluid.

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Membrane Proteins

• Membrane proteins can have many functions
• transporters
• enzymes
• receptors
• cell surface identity markers (name tags)
• cell adhesion proteins
• attachments to cytoskeleton

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Plasma Membrane Proteins
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MOVEMENT ACROSS THE CELL MEMBRANE

• Can be either passive or active
• Passive requires no energy from the cell
• Active needs cell energy in order to work

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Passive Transport

• Types
• 1.) Diffusion
• An overall (net) movement of substances from a
  region of high concentration to a region of low
  concentration.

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Selective Membrane Transport

• The cell membrane is considered selectively
  permeable, because only certain molecules are
  allowed to enter.

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2.) Facilitated Diffusion

• Uses proteins
• Does not require energy.
• Molecules attach to the proteins and are brought
  into the cell.

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Facilitated Diffusion
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3.) Osmosis

• diffusion of water across a membrane.
• Water moves towards the higher solute
  concentration.
• Solutes are particles dissolved in the liquid.

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Osmosis

• Osmotic concentration - concentration of all
  solutes in solution
• Hypertonic -more solute outside the cell than
  inside.
• Hypotonic - more solute inside the cell than
  outside.
• Isotonic - solute concentrations inside and
  outside are equal

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EFFECT of OSMOSIS on RED BLOOD CELLS
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Maintaining Osmotic Balance
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Active Transport

• Types
• 1.) Active transport involves the use of energy
  to move substances against their concentration
  gradient (uphill).
• Often involves highly selective protein carriers
  within the membrane
• Example
• sodium-potassium pump

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2.) BULK TRANSPORT
Another type of active transport. ARRGH WHEN
DOES IT STOP!!!???!!!
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Bulk Transport

• REQUIRES ENERGY!!!
• Endo- into
• Exo- out of
• Types of Bulk Transport
• 1.) Endocytosis - the movement of material into
• the cell.
• Examples
• phagocytosis - solids are taken into the cell.
• pinocytosis - Liquids are taken into the cell.
• receptor-mediated endocytosis - transport of
  specific molecules such as cholesterol.
• 2.) Exocytosis - discharge of material out of the
  cell from vesicles at the cell surface

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