Cell Membrane Composition and Functions

History of the Cell Membrane

• Garde Nicholson and Jonathan Singer proposed the fluid mosaic model in 1932

Composition of the Cell Membrane

• Phospholipids (40%): found throughout the cell membrane
• Proteins (50%): embedded in the phospholipid bilayer, can be found in the peripheral or interior of the membrane
• Carbohydrates (10%): found only on the exterior of the cell membrane
• Cholesterol: attached to phospholipids

Functions of Each Biomolecule

• Phospholipids:
  • Have a polar, hydrophilic head and a non-polar, hydrophobic tail
  • Form a bilayer with hydrophilic heads facing outward and inward, and hydrophobic tails facing inward
  • Allow water to pass through, but not other substances
• Cholesterol:
  • Helps maintain fluidity of the membrane at different temperatures
  • Increases fluidity at low temperatures, decreases fluidity at high temperatures
• Proteins:
  • Integral proteins: span the entire membrane
  • Peripheral proteins: found on the periphery of the membrane
  • Two types of integral proteins:
    • Channel proteins: form a channel for molecules to pass through
    • Transport proteins: change conformation to transport molecules across the membrane
• Carbohydrates:
  • Form a glycocalyx (glycoproteins and glycolipids) on the exterior of the cell membrane
  • Help the cell recognize its surroundings and interact with other cells and molecules

Functions of the Cell Membrane

• Protects the cell and its organelles
• Regulates transport of substances into and out of the cell
• Helps the cell recognize and interact with its surroundings
• Important for compatibility in organ transplants and blood transfusions

History of the Cell Membrane

• Garde Nicholson and Jonathan Singer proposed the fluid mosaic model in 1972 (not 1932)

Composition of the Cell Membrane

• Phospholipids make up 40% of the cell membrane and are found throughout
• Proteins account for 50% of the cell membrane and are embedded in the phospholipid bilayer
• Carbohydrates make up 10% of the cell membrane and are only found on the exterior
• Cholesterol is attached to phospholipids

Phospholipids

• Have a polar, hydrophilic head and a non-polar, hydrophobic tail
• Form a bilayer with hydrophilic heads facing outward and inward, and hydrophobic tails facing inward
• Allow water to pass through, but not other substances

Cholesterol

• Helps maintain fluidity of the membrane at different temperatures
• Increases fluidity at low temperatures, decreases fluidity at high temperatures

Proteins

• Integral proteins span the entire membrane
• Peripheral proteins are found on the periphery of the membrane
• There are two types of integral proteins:
  • Channel proteins form a channel for molecules to pass through
  • Transport proteins change conformation to transport molecules across the membrane

Carbohydrates

• Form a glycocalyx (glycoproteins and glycolipids) on the exterior of the cell membrane
• Help the cell recognize its surroundings and interact with other cells and molecules

Functions of the Cell Membrane

• Protects the cell and its organelles
• Regulates transport of substances into and out of the cell
• Helps the cell recognize and interact with its surroundings
• Important for compatibility in organ transplants and blood transfusions