Brent Cornell

    
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  

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

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