The relationship lead to the permanent association and integration leading to eventual evolution of eukaryotes.
Membranes that may be double or single layered line cell organelles. The Mitochondria, chloroplast and the nucleus (not strictly an organelle) have double layered membranes, while the Lysosomes, Golgi apparati, vacuoles and so on have a single membrane. The Ribosomes are non-membranous structures.
The structural representation in the fluid mosaic model of the plasma membrane is universal in all living cells (plants & animals) and consists of two layers of phospholipids (lipids attached to a phosphate unit, proteins that dynamically move about the membrane and a small amount of glycoproteins (glucose bonded to proteins).
The lipid molecules are "amphiphilic," having a hydrophilic (water loving) portion facing outside and a hydrophobic (water shunning) lipid portion turned inside. (Campbells' Biology Chapter 8; Dalton.M Chapter2/membrane/html.)
Primarily, there are10 different types of lipids reported in cell membranes with different types of cells/organelles having differing percentage of each lipid, protein, and carbohydrate. They are: (1)Cholesterol, (2)Glycolipids, (3) Phosphatidylcholine, (4)Sphingomyelin, (5)Phosphatidylethnolamine, (6)Phosphatydilinositol, (7)Phosphatidylserine, (8) Phosphatidylglycerol, (9)Diphosphatidylglycerol (Cardiolipin), (10)Phosphatidic acid (Dalton.M Chapter2/membrane/html).
Proteins in the cell membrane may have limited movement (being bound to the cell's exoskeleton or other membrane structures) or move freely if unbound (Campbells' Biology Chapter 8; Cellmembranes.html 10 Aug. 2003) . These proteins could be in the hydrophobic (integral proteins) or in the hydrophilic (peripheral proteins) regions. The proteins vary in structure and function but have distinct directional orientation (Campbells' Biology Chapter 8).
The membranes are responsible for maintaining an almost constant cell or organelle environment. For instance the pH with the Lysosome is maintained at 5. This has been made possible by the selective permeability of the membrane that allows ready entry of glucose, amino acids and lipids and prevents the exit of metabolic intermediates while allowing external passage of wastes. The membranes' hydrophobic portions are typically impermeable to water-soluble materials like glucose, amino