The Plasma Membrane

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The Plasma Membrane

• Chapter 7.2

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I. The Plasma Membrane Surrounds the Cell.

• Boundary between the cell and its watery
  environment.
• Gateway for materials to enter and exit
  the cell (ex
  nutrients
• and waste).
• Function maintain
• homeostasis (balance)
  
• for the cell.

Plasma Membrane
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• The Plasma Membrane is a selectively permeable
  membrane.
• Allows some molecules to enter and keeps others
  out
• Selective barrier (like a screen door, coffee
  filter)

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II. Structure of the Plasma Membrane

• Composed of two layers of phospholipids, called
  the phospholipid bilayer.
• Phospholipids are lipids
  with a phosphate attached
  to them.

Phospholipid molecule
Polar head (includes phosphate group)
Nonpolar tails (fatty acids)
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• The phosphate head is polar
  (hydrophilic loves water), so it interacts with
  the watery environment inside the cell and
  outside the cell.
• The fatty acid tails are nonpolar (hydrophobic
  afraid of water) so they
  avoid
  water.

Polar heads love water
Non-polar tails hide from water
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The Fluid Mosaic Model of the Plasma Membrane
http//www.stolaf.edu/people/giannini/flashanimat/
lipids/membrane fluidity.swf

• Fluid because it moves like water
• Mosaic because the proteins make a pattern on the
  surface.

Carbohydrate chains
Proteins
Transport Protein
Phospholipids
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III. Other parts of the Plasma Membrane

• 1. Cholesterol stabilizes the phospholipids
  and prevents the fatty acid tails from sticking
  together.

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1. Transport proteins move needed substances and
   waste through the plasma membrane, they regulate
   which molecules enter and leave.

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1. Inner surface proteins give cell its
   flexibility
2. Carbohydrate chains stick out from the surface
   of plasma membrane, identifies chemical signals
   and other cells.

Carbohydrate chains
Proteins
Transport Protein
Phospholipids