4.1 Structure of the
cell-surface membrane
,Plasma membranes
• These are all membranes around and within cells
• Have same basic structure
• Cell-surface membrane is the plasma membrane that surrounds ce
and forms boundary between cytoplasm and outside of cell
,Phospholipids
• Molecular structure of phospholipid: hydrophilic phosphate head, t
hydrophobic fatty acid tails, glycerol, ester bond
• Hydrophilic heads point to outside of membrane as there is water o
both sides
• Hydrophobic tails pint into the cell membrane to avoid water
• They transport lipid-soluble substances
Function
• Transport lipid-soluble substances into/out of cell
• Prevent water-soluble substances going into/out of cell
• Flexible and self-sealing membrane
, Proteins
• Some occur on surface of bilayer [extrinsic proteins] and give
mechanical support/as cell receptors
• Some extend through the bilayer as proteins channels or carrier
proteins
• Channels: water-filled tubes so water-soluble ions can diffuse across
• Carrier: bind to ions/molecules and change shape to transport them
Function
• Structural support
• Channels to transport water-soluble substances
• Active transport across membrane via carrier proteins
• Form cell-surface receptors for identifying cells or act as receptors
• Help cells adhere together
cell-surface membrane
,Plasma membranes
• These are all membranes around and within cells
• Have same basic structure
• Cell-surface membrane is the plasma membrane that surrounds ce
and forms boundary between cytoplasm and outside of cell
,Phospholipids
• Molecular structure of phospholipid: hydrophilic phosphate head, t
hydrophobic fatty acid tails, glycerol, ester bond
• Hydrophilic heads point to outside of membrane as there is water o
both sides
• Hydrophobic tails pint into the cell membrane to avoid water
• They transport lipid-soluble substances
Function
• Transport lipid-soluble substances into/out of cell
• Prevent water-soluble substances going into/out of cell
• Flexible and self-sealing membrane
, Proteins
• Some occur on surface of bilayer [extrinsic proteins] and give
mechanical support/as cell receptors
• Some extend through the bilayer as proteins channels or carrier
proteins
• Channels: water-filled tubes so water-soluble ions can diffuse across
• Carrier: bind to ions/molecules and change shape to transport them
Function
• Structural support
• Channels to transport water-soluble substances
• Active transport across membrane via carrier proteins
• Form cell-surface receptors for identifying cells or act as receptors
• Help cells adhere together
