cell membrane

Cell membrane is a biological membrane that separates the interior of all cells from the outside environment (the extracellular space) The basic function of the cell membrane is to protect the cell from its surroundings. The cell membrane controls the movement of substances in and out of cells

 and organelles

 composition of cell membrane :

1-       Lipid

      The cell membrane consists of three classes of amphipathic lipids: phospholipids,    glycolipids, and sterols.

2-      carbohydrates  :

Plasma membranes also contain carbohydrates, predominantly glycoproteins, but with some glycolipids (cerebrosides and gangliosides). Carbohydrates are important in the role of cell-cell recognition in eukaryotes; they are located on the surface of the cell where they recognize host cells and share information,

3-      protein

protein are important for the cell , they are responsible for various biological activities , membrane protein consist of 3 main type , integral protein , peripheral protein and lipid anchored protein

1-  transmembrane proteins     Span the membrane and have a hydrophilic cytosolic domain, which interacts with internal molecules, a hydrophobic membrane-spanning domain that anchors it within the cell membrane, and a hydrophilic extracellular domain that interacts with external molecules.

2-  peripheral protein  associated with peripheral regions of the lipid bilayer. These proteins tend to have only temporary interactions with biological membranes, and once reacted, the molecule dissociates to carry on its work in the cytoplasm.   Some enzymes, some hormones

3-  -lipid anchored Covalently bound to single or multiple lipid molecules; hydrophobically insert into the cell membrane and anchor the protein.            

Function of cell membrane

1-The cell membrane surround the cytoplasm of living cell physically separating the intracellular component from extracellular environment , it also play a role in anchoring the cytoskeleton and in attachment to extracellular environment

2-Some substances (small molecules, ions) such as carbon dioxide (CO2) and oxygen (O2), can move across the plasma membrane by diffusion, which is a passive transport process, osmosis involve a solvent moving through semipermeable membrane from are of low concentration to high

osmosis

3-Transmembrane proteins extend through the lipid bilayer of the membranes; they function on both sides of the membrane to transport molecules across it Nutrients, such as sugars or amino acids, must enter the cell, and certain products of metabolism must leave the cell.