Unit 1: Biochemistry - #4 Role of Membrane Proteins

Integral vs Peripheral Membrane Proteins

All membrane proteins can be separated into these two additional categories

1. Integral Membrane Protein → Embedded in the lipid bilayer

2. Peripheral Membrane Protein → On the surface of the lipid bilayer

Integral/Transmembrane Proteins

• Span the entire bilayer and are exposed to the aqueous environment on both sides of the membrane

• Within Membrane - Non polar amino acids are hydrophobic which matches the hydrophobic region of the phospholipid tails

• Outer Membrane - Polar amino acids are hydrophilic and extend into the extracellular fluid on the outside and into the cytoplasm on the inside

• Transport Proteins → Acts as channels or pumps

Peripheral Proteins

• Loosely bound to the surface of the cell membrane

• Do not interact with the hydrophobic core of the membrane

• Outer Surface - They hold onto the surface of the membrane with ionic and H-bonds. Most are on the extracellular side of the membrane, but some are on the cytoplasm side as well.

• Act as cell identity markers (antigens) or receptors

• Inner Surface - Anchor points for microtubules or microfilaments

Membrane Carbohydrates

• Some of the membrane lipids and proteins have carbohydrates linked to them.

• Called glycolipids (any membrane lipid + carbohydrate) or glycoproteins (membrane component with sugar or carb + aa)

• Crucial for cell-cell recognition and signaling

• Allows the cell to distinguish one cell from another and to identify foreign cells or particles (bacterial or viral infections)

• Recognize and bind to carbohydrate receptors on adjacent cells and leads to attachment between cells