Three classes of membrane protiens

Membrane Proteins

Types of Membrane Proteins

• Proteins associated with the cell membrane are classified based on their attachment:
  • Integral membrane proteins.
  • Peripheral membrane proteins.
  • Lipid-anchored membrane proteins.

Integral Membrane Proteins

• Embedded within the lipid monolayer(s).
• Monotopic: Embedded in just one monolayer.
• Transmembrane: Span through both monolayers of the lipid bilayer.
  • Can pass through the bilayer once or multiple times, depending on protein length and function.
  • Multiple passes may create openings for substance transport.

Peripheral Membrane Proteins

• Sit against one of the monolayers.
• Attached through weak electrostatic forces rather than covalent bonds.
• Easily released from the membrane by changing the pH or other environmental factors.

Lipid-Anchored Membrane Proteins

• Hydrophilic, located on the membrane surface.
• Covalently bound to lipids in the bilayer.
• Permanently attached until the bond is broken, unlike peripheral proteins.

Glycoproteins and Glycosylation

• Proteins with carbohydrate chains attached, similar to glycolipids.
• The process of attaching carbohydrates is called glycosylation.
• Glycosylation starts in the endoplasmic reticulum (ER) and continues in the Golgi apparatus.
  • Plays a role in cell recognition.
  • The carbohydrate chains on glycolipids determine blood type, acting as antigens.