Cell Membrane Structure and Function

Amino acids are large molecules which are pumped across the membrane by transmembrane transporters.

Small molecules or ions such as carbon dioxide (CO₂) and oxygen (O₂) can move across the plasma membrane by passive osmosis.

Periplasm is found in Gram negative bacteria. Gram negative bacteria have both a plasma membrane and an outer membrane separated by periplasm.

Besides being selectively permeable, plasma membrane of eukaryotes also functions in synthesis of ATP through chemiosmosis.

Cell membrane is impermeable to charged polar molecules like glucose-6-phosphate.

Caveolae are the small invaginations of plasma membrane of many vertebrate cell types, especially in endothelial cells and adipocytes. These are rich in proteins and lipids.

Podosomes are connected to cellular motility and invasion. Therefore, they serve as sites of attachment and degradation along the extracellular matrix.

Lipid rafts and caveolae microdomains of the cell membrane are rich in cholesterol.

The actin-based filaments formed by cytoskeleton in order to sense the external environment are called filopodia. They are rich in actin-binding proteins, e.g. fascin and fimbrin. Filopodia are slender cytoplasmic projections that form focal adhesion with the substrate linking it to the cell surface.

Cell membrane of myocytes is known as sarcolemma. It consists of a plasma membrane, which is a lipid bilayer, and an outer coat consisting of a thin layer of polysaccharide material (glycocalyx) that contacts the basement membrane, which contains numerous thin collagen fibrils and specialized proteins such as laminin that provide a scaffold for the muscle fiber to adhere to it.

When the pump binds two molecules of K+ to their respective bonding sites on the extracellular face of the transport protein, dephosphorylation of the pump occurs.

G-proteins are an example of lipid-anchored proteins. G-proteins act as molecular switches inside the cell and are involved in transmitting signals from a variety of stimuli outside a cell to its interior.

The inner mitochondrial membrane is very rich in proteins. It contains proteins in the form of enzymes required for electron transport chain.

Fluid mosaic model about the structure and function of membrane was given by Singer and Nicolson in 1972.

Sphingolipids are not found in cell membrane.