Membrane Structure and Transport

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Membrane Structure and Transport
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Membrane Structure

• Phospholipid bilayer (nonpolar)
• Membrane proteins act as transport channels
• Carbohydrate chains act as ID tags for the
  cell
• Cholesterol provides stability for the membrane

http//library.thinkquest.org/C004535/media/cell_m
embrane.gif
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Membrane Functions

• Provides a selectively permeable barrier around
  the cell
• Controls the passage of substances in and out of
  the cell.
• Polar and charged substances can pass through the
  membrane proteins (gates)
• Maintains homeostasis for the cell helping it
  meet its needs.

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Types of Cellular Transport

• ACTIVE
• Requires energy from ATP
• Goes against the concentration gradient (low to
  high)
• Active Transport, Endocytosis, Exocytosis

• PASSIVE
• Does not require energy
• Goes with the concentration gradient (high to
  low)
• Simple Diffusion, Facilitated Diffusion

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Simple Diffusion

• Particles move from areas of high to low
  concentration
• This continues until equilibrium is reached
• Random motion of particles and a concentration
  gradient drive diffusion.

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Facilitated Diffusion

• Particles are moving through a transport protein
  from high to low concentration
• Particles that are polar are charged must move
  through a protein channel
• Glucose and ions enter the cell in this way.

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Osmosis

• Osmosis is the diffusion of water through a
  selectively permeable membrane.
• Water will move to the side of the membrane that
  has the higher solute concentration.

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Osmosis

• Cells will shrivel when put into a solution with
  MORE SOLUTE. Ex) salt water
• If solute concentration is equal on both sides of
  the membrane, the cell does not change.
• Cells will swell or burst when put into a
  solution with LESS SOLUTE Ex) Fresh water

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Active Transport

• Particles move from low to high concentration
  against concentration gradient
• Requires ATP energy
• The sodium / potassium pump is an example.

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Endocytosis

• The plasma membrane surrounds and brings large
  particles into the cell
• Phagocytosis cell eating
• Pinocytosis cell drinking
• Requires energy

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Exocytosis

• The export of large particles such as waste out
  of the cell
• Proteins, hormones, and other substances are
  secreted from cells in this manner
• Nerve cells release neurotransmitters in this
  manner