Describe, with the aid of a diagram, the structure of the cell membrane, and transmembrane transport processes.

Master answer

Structure of Cell Membrane

Cell Membrane

• Made of
  • Phospholipids
  • Proteins
  • Cholesterol – Found in eukarocytes ie cells with nuclei
• Cell membrane = 7.5nm thick semi permeable structure

Lipid Bilayer

• Fluid rather than solid
• Phospholipids have:
  • eg phosphatidyl-choline & phosphatidyl-ethanol-amine
  • Hydrophilic head
    • Water soluble
    • Exposed to aqueous exterior & interior
  • Glycerol backbone
  • Fatty acid tails –
    • Hydrophobic
    • Meet in middle of cell membrane
• Proteins can be either:
  • Integral – ie pass through bilayer eg ion channels
  • Peripheral = straddling
    • make up 50% of cell membranes mass

Function of CM Proteins

• Structural
• Carriers for facilitated diffusion (i.e. down electrochemical gradient)
• Pumps for ion active transport
• Ion channels (diffusion down electro- or chemical gradient or both; e.g. K-“leak” channels)
• Receptors for chemical messengers (i.e. hormones , neurotransmitters , autacoids…)
• Enzymes
• Glycoproteins involved in AB processing or anticoagulation (e.g. the mucopolysaccharide glycocalyx of the endothelium which repels clotting factors + PLT’s → helps prevent blood from clotting in intact blood vessels)

Transmembrane Transport Processes

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Mooney / JC 2019

Answer by JC, Mooney