Chapter 1 Structure and Functions of Biomembranes

Abstract

Publisher Summary This chapter discusses the structure and functions of biomembranes, and highlights the specialized roles of mitochondria and peroxisomes. Cell membrane systems provide two important functions: (1) They establish a biological barrier to the extracellular environment, and (2) they compartmentalize specialized and sometimes toxic biological reactions within the cell. Mitochondria consist of a double membrane system, with an extensive inner membrane surface area. The mitochondrial membrane system is second, only to the endoplasmic reticulum membrane surface area, often consisting of up to 40% of the total membrane in a cell. Because of this vast membrane network, mitochondria occupy a large portion of the cytoplasmic volume of cells, and in many cell types, are constantly changing shape. Rather than the rod-like structures often depicted in textbooks, they are more often seen as elongated string-like structures. Mitochondrial movement occurs in a number of cell types and is mediated by microtubules. Although, the mitochondrial genome encodes for 33 genes, the vast majority of proteins are made by the cell and are imported by the mitochondrial transporters of the outer and inner membranes, the translocase of the inner membrane (TOM) and translocase of the inner membrane (TIM) complexes. The most commonly associated function of mitochondria is in the production of ATP from oxidative phosphorylation. Peroxisomes are small, single membrane organelles that contain a number of oxidative enzymes. One unique function is in the production of plasmalogens, the most abundant lipid found in myelin.