TWO - The structure of the cell membrane

Abstract

This chapter discusses the structure of the cell membrane. It has been suggested that cell membrane contained either pure lipid or pure protein, with pores about the size of a large molecule, or that it was in the form of a mosaic containing either pure lipid or pure protein in various areas. A common structure for the cell membrane exists in cells as diverse as erythrocytes, axons of nerve cells, muscle fibers, leucocytes of the blood, yeast cells, algal cells, and the ova of the echinoderms. There are variations to some extent between the membranes of the various cells. In the apical region of cells, the plasma membrane may be folded into fingerlike projections called microvilli. These are very numerous in the apical borders of kidney tubule cells and those of the small intestine. These villi are completely covered with unit membrane. There is evidence of presence of pores in the plasma membrane and these pores may be open or closed and since they are present in large numbers in the plasma membrane when they are open, they compress the membrane into a series of pillars composed mainly of lipid.