Membrane Proteins

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•  Membrane proteins are diverse in terms of structure, position in the membrane and function

Phospholipid bilayers are embedded with proteins, which may be either permanently or temporarily attached to the membrane

  • Integral proteins are permanently attached to the membrane and are typically transmembrane (they span across the bilayer)
  • Peripheral proteins are temporarily attached by non-covalent interactions and associate with one surface of the membrane  

channel protein

Structure of Membrane Proteins

The amino acids of a membrane protein are localised according to polarity:

  • Non-polar (hydrophobic) amino acids associate directly with the lipid bilayer 
  • Polar (hydrophilic) amino acids are located internally and face aqueous solutions

Transmembrane proteins typically adopt one of two tertiary structures: 

  • Single helices / helical bundles 
  • Beta barrels (common in channel proteins)

Membrane Protein Structures

membrane protein structures

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Functions of Membrane Proteins

Membrane proteins can serve a variety of key functions:

  • Junctions – Serve to connect and join two cells together 
  • Enzymes – Fixing to membranes localises metabolic pathways 
  • Transport – Responsible for facilitated diffusion and active transport 
  • Recognition – May function as markers for cellular identification 
  • Anchorage – Attachment points for cytoskeleton and extracellular matrix 
  • Transduction – Function as receptors for peptide hormones 

Mnemonic:  Jet Rat

Membrane Protein Functions

membrane protein functions 2