Bacteriorhodopsin Bacteriorhodsin, dealing with the light absorption, contains seven alpha-helical transmembrane segments which span the membrane. Each is connected to the next by a loop of hydrophilic amino acids which extend into or through the polar membrane surfaces. Other membrane proteins contains as many as 20 or more transmembrane segments, and some proteins have one or more beta-strand segments which span the membrane interior. Therefore, structures such as the beta barrel, where the beta strands are wound into a cylinder which allows interstrand hydrogen bonds to form, are more likely. This unique segregation produces proteins which have distinct polar and nonpolar regions.
Glycoproteins are proteins which have attached carbohydrate groups.
The carbohydrate groups of proteins link into straight or branch chains containing up to 60 residies. In Glycoproteins, the carbohydrate group is linked to the protein segments of the molecules in two distinctly different patterns. These glycoproteins are most abundant in plasma membranes. The carbohydrates' function in glycoproteins is believed to be that it adds stability to membranes and adds to the forces which fold and maintain membrane proteins into their correct 3-dimensional form. In water, phospholipids spontaneously assemble into bilayers .