Eucaryotic Cell Organelles

A eucaryotic cell has excessive foldings of intrace!:u:;ir cembrane as compared to procaryotic cell. The eucaryotic cell has a number of'organelles such as endoplasmic reticulum, Golgi apparatus, nucleus, mitochondria etc. Organelles have the same relation to a cell, as organs have with an organism. The endoplasmic reticulum is a complex system of membranous sacs, chambers, and tubular canals. It is the site for synthesis of proteins. The Golgi apparatus (or complex) which is a stack of flattened sacs sorts out and processes proteins, besides, it helps in secretion. Membranes also enclose lysosomes, the organelles that contain enzymes necessary for degrading foreign materials thereby help in defence mechanisms. Likewise, membranes surround peroxisomes (microbodies) in which highly reactive hydrogen peroxide is synthesised and degraded. Peroxisomes are also the sites where a variety of biochemical reactions cause conversion of lipids into proteins and v+~ ,e-aversa. In plants, the membranes surround large liquid filled vacuoles. The remaining cytoplasm which is not bound by these organelles is referred to as the cytosol.

The extensive intracellular membrane system of a eucaryotic cell is much larger in size than a procaryotic cell. It provides enough surface area for the exchange of materials and other important cellular reactions which take place on the membrane surface.

It is assumed that membranous organelles have been formed by infolding of plasma membrane through a process called endocytosis (Figure shown below). In endocytosis portions of cell membrane along with the contents of the external medium invaginate and pinch off in the form of cytoplasmic vesicles. Exocytosis is just a reverse process.