Transport across the plasma membrane

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Transport across the plasma membrane
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Structure of the plasma membrane

• This diagram shows the currently accepted fluid
  mosaic model for the membrane structure.
• The plasma membrane is made of of a phospholipid
  bilayer (two layer). The membrane has many
  proteins embedded in it, some forming protein
  channels.
• The plasma membrane regulates what enters and
  leaves the cell. Many molecules cross the cell
  membrane constantly to supply the cell with its
  needs and remove its wastes.

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• The plasma membrane is partially/selectively/diffe
  rentially permeable
• Materials can cross the membrane in different
  ways.
• Large amounts of material requires bulk transport
  via endocytosis/exocytosis
• Small (molecular) amounts move in and out of
  cells via
• Diffusion
• Facilitated diffusion
• Osmosis
• Active transport

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Endocytosis

• Endocytosis is the cellular uptake of molecules
  and other substances by regions of the plasma
  membrane that surround the substance and pinch
  off to form an intracellular vesicle.

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Exocytosis

• Exocytosis is the secretion of macromolecules by
  the fusion of vesicles with the plasma membrane.

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Diffusion

• Simple diffusion is the movement of substances
  form a higher-concentration region to a
  lower-concentration region.

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Facilitated diffusion

• Facilitated diffusion is the movement of
  substances from a higher-concentration region to
  a lower-concentration region with the assistance
  of an integral protein across a selectively
  permeable membrane.

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Osmosis

• Osmosis is the net movement (diffusion) of a
  solvent (water in living organisms) from a region
  of higher water concentration to a region of
  lower concentration.

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Tonicity is a relative term

• Hypotonic Solution - One solution has a lower
  concentration of solute than another.
• Hypertonic Solution - one solution has a higher
  concentration of solute than another.
• Isotonic Solution - both solutions have same
  concentrations of solute.

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Plant and Animal Cells put into various solutions
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Osmosis and Animal Cells
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Active Transport

• Active transport is the net movement of dissolved
  substances through a cell membrane against its
  concentration gradient (from low to high
  concentration). This is a process requiring
  metabolic energy.