y-chain B-cr 1.27A C1 ) AMl-trans 4.6A 2 gi ki Fg. 2-14. Structure of 1. 2-diacylphosphatidylcholine molecule emphasizing the relative orientation and conformation of the head group and of the acyl chain. The lower part of the figure illustrates an alkyl chain in an all-trans and par -gauche conformations.The Newman projections for the trans and gauche conformations are also shown. The dihedral angle (Cr-Cu)is 180 for the trans conformation and 120 or 240" for the gauche conforma- tion. The 2gl kink is formed by rotating about one C-c bond by an angle of 120"and then otating about either of the two next nearest neighboring bonds by -120