PLASMA MEMBRANE

• Phospholipid bilayer: bilayer that comprises mostly phospholipids
• Fluid mosaic: mosaic of proteins embedded within a fluid phospholipid bilayer
• Selectively permeable: some substances move through passively, others use proteins for transport

MEMBRANE COMPONENTS

• Phospholipids
• Proteins
• Cholesterol
• Carbohydrates

PHOSPHOLIPIDS

• Amphipathic: hydrophilic head and hydrophobic fatty acid tails
• Form liposomes in aqueous environment
• Weak hydrophobic interactions = membrane fluidity
• Saturated phospholipids: maximize hydrogens in fatty acid tails, no kinks
• Unsaturated phospholipids: double bond produces kink, increases fluidity

CHOLESTEROL

• Temperature buffer
• Moderate temperature: decreases fluidity, lessens lateral movement
• Low temperature: increases fluidity, prevents solidification

PROTEINS

• Includes transmembrane proteins that span the bilayer (other types exist)
• Proteins provide about half the mass of the membrane

CARBOHYDRATES

• Glycoproteins: branched carbohydrates covalently bound to proteins
• Glycolipids: carbohydrates covalently bound to lipids (extracellular only)

CLINICAL CORRELATION:

Blood types

• Carbohydrates on surface of red blood cells must be compatible between donor & recipient in blood transfusion

FUNCTIONS OF THE CELL MEMBRANE

• Cell communication
• Import and export of molecules
• Cell growth
• Cell motility

Eukaryotes have internal membranes within the cell, prokaryotes do not.