Cell membrane proteins | Cells | MCAT | Khan Academy

Overview of Membrane Proteins

• The significance of membrane proteins in cell membranes can be up to 75%, though typically around 50%.

• Membrane proteins are vital for various cell membrane functions.

Structure of the Cell Membrane

• Comprised primarily of phospholipids forming a lipid bilayer.

  • The lipid bilayer includes two layers of phospholipids.

Types of Membrane Proteins

Integral Proteins

• Integral proteins are embedded throughout the membrane and difficult to remove.

• They play crucial roles in cell functions and can span the entire membrane.

Peripheral Proteins

• Peripheral proteins are located on the outer layer or may attach to integral proteins.

• Easier to detach than integral proteins, they often facilitate specific cell processes like hormone signaling.

Lipid-Bound Proteins

• Rare and located within the membrane, these proteins interact with the internal environment.

• They are less functional for external interactions due to their location.

Important Integral Proteins

Channel Proteins

• Form a channel through which ions (e.g., Na+) pass into and out of the cell.

• Facilitate passive transport, not requiring energy, and operate based on concentration gradients (moving from high to low concentration).

Carrier Proteins

• Carry specific molecules into the cell and can also transport substances out.

• Unlike channel proteins, they can actively transport substances against concentration gradients, sometimes requiring ATP.

  • Example: Bringing in chloride ions despite high internal concentrations.

Glycoproteins

• Combinations of sugars and proteins that exist on various proteins.

• Serve as signaling molecules for cell recognition, crucial for communication and interaction between cells.

Summary of Membrane Proteins

• Peripheral Proteins: Easy to remove, located outside the membrane.

• Integral Proteins: Embedded in the membrane, challenging to detach.

• Lipid-Bound Proteins: Rare, internal membrane presence.

• Channel Proteins: Allow passive ion flow based on concentration gradients.

• Carrier Proteins: Protect molecules while transporting, can move substances against gradients, sometimes using ATP.

• Glycoproteins: Signal and facilitate cell recognition.