The structure and function of the plasma membrane

Plasma membrane

The plasma membrane is a selectively permeable barrier controlling the passage of substances in and out of the cell.

• double layer of phospholipids with embedded proteins

• Physical barrier separating the inside/outside of cell

Much of our body is hydrophilic

Fats are hydrophobic

Fats in cell membrane provide a barrier to water

Phospholipid

• hydrophilic polar heads (phosphate)

• hydrophobic lipid tails (fatty acids)

• arranged as a double layer around cytoplasm, tail to tail

Plasma Membraine Proteins

Membrane proteins mediate movement of hydrophilic substances

• Are often amphipathic, meaning they have both hydrophilic and hydrophobic regions

Integral proteins

• embedded partially or fully into the membrane

Peripheral membrane proteins

• associated with the membrane, but not actually embedded in it

Allow cell-celll identification and facilitate intercellular communication

Plasma membrane proteins main functions

Transport

• channels, transporters, may be general or selective, gated or not

Enzymatic activity

• carry out chemical reaction, may or may not be a part of a team of enzymes

Signal transduction

• external signalling molecule causing communication of information to the inside of the cell

Plasma membrane proteins other functions

Cell-Cell recognition

• use of glycoproteins (carbohydrate + protein) as molecular signatures of the extracellular side of the cell

Intercellular joining

• e.g. gap unctions or tight junctions

Attachment to the cytoskeleton and extracellular matrix (ECM)

• e.g. fibronectin mediates contact between cell surface integrins and ECM can facillitate movement

Membranes are not static

• the membrane is a mosaic of molecules bobbing in a fluid layer of phospholipids

• cell specific and dynamic repertoire of membrane-bound proteins present as required