Cell Membrane

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Cell Membrane
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Function of Cell Membrane

• Separates the cells contents from materials
  outside the cell
• Regulates what moves in and out of a cell
• without the cell membrane to contain the
  substances the cell needs for life, the cell
  would die.

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Structure of Cell Membrane

• -composed of groups of organic compounds
  (glycolipids, glycoproteins, proteins,
  cholesterol, and phospholipids)
• Phospholipid shaped like a head with 2 tails
• -made from a phosphate group connected to 2 fatty
  acid tails (forms a double layer called a lipid
  bilayer)

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Structure of Phospholipid
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Why are the phospholipids arranged tail to tail?

• -b/c water is inside and outside the cell
• phosphate group is hydrophilic (polar) end
• -attracts water
• fatty acid tail end is hydrophobic (nonpolar)
• -repels water

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Arrangement of phospholipids tail to tail
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Polar vs. Nonpolar

• Polar- positive and negative ends (b/c electrons
  are not shared equally)
• Ex. Water
• Nonpolar- does not have oppositely charged ends
  (atoms share electrons equally)

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Arrangement of phospholipids tail to tail due
to water inside outside the cell
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Fluid Mosaic Model of Cell Membrane

• -lipid bilayer is not strong firm like a hard
  shell, but it is fluid like a soap bubble (often
  called a fluid mosaic model)
• -individual phospholipids, arranged side by side,
  float within the bilayer (cholesterol prevents
  phospholipids from sticking together)

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Structure of Cell Membrane

• -nonpolar interior zone- true barrier that
  separates the cell from its surroundings
• many polar particles like sugars, proteins, ions,
  most cell wastes cannot cross this zone b/c
  they are repelled by the nonpolar region

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Whats in the cell membrane?

• Solution?
• -passageways through the barrier that enable the
  cell to regulate what substances go in and out.
• Cell Surface Proteins- proteins embedded within
  the plasma membrane of cells
• Proteins- 50 to 70 of cell membrane

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Types of Cell Surface Proteins

• Channel Proteins- act as gates to the cell
  interior, transporting food other molecules
  (sugar, proteins, ions) in wastes out

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Types of Cell Surface Proteins

• Receptor proteins- information receivers they are
  the informers of the cell, gathering information
  about the cells surroundings
• many hormones act by binding to specific
  receptor proteins
• Ex. Glycoproteins- combination of protein and
  carbohydrates
• Ex. Integral proteins- span entire range of cell
  membrane

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Types of Cell Surface Proteins

• Marker proteins- name tags of the cell
  identifies what kind of cell it is (ex. Liver
  cell, heart cell, or brain cell)
• marker proteins have long exterior arms that
  often have carbohydrates attached to them
• Ex. Glycoproteins or glycolipids

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Arrangement of cell surface proteins
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Cell Membrane Structure