Biology 12

3.4 Plasma Membrane Structure and Function

The plasma membrane regulates entrance and exit of substances from the cell to help maintain homeostasis.

The fluid-mosaic model of the plasma membrane structure:

· Phospholipids form a bilayer, with the hydrophilic polar heads facing inside and outside of the cell and hydrophobic tails facing each other

· Peripheral proteins are partially embedded on one side of the membrane

· Integral proteins span the entire membrane and may protrude into one or both sides; they move laterally

· Steroids, glycolipids, and glycoproteins are also present

Functions of the Membrane Proteins

Plasma membranes of different cell types have unique combinations of proteins. Generally,

· Peripheral proteins play a structural role by helping to stabilize and shape the plasma membrane

· Integral proteins determine a membrane’s specific functions. The following are types of integral proteins:

· channel proteins

· carrier proteins

· cell recognition proteins

· receptor proteins

· enzymatic proteins

Types of the Membrane Proteins

Channel proteins are involved in the passage of molecules through the cell membrane by forming a channel.

Carrier proteins are involved in the passage of molecules through the cell membrane by combining with the substance.

Cell recognition proteins are glycoproteins involved in cell recognition of pathogens.

Receptor proteins bind specific molecules, which causes a cell response.

Enzymatic proteins catalyze cell reactions.