胆固醇结构式 (a) 18 (b) 2 12 17 CH3 11 13 16 2 19 5 25HC- CH3 10 B 8 1 24CH2 23CH2 22CH2 HC20CHa 18 21 a 1 CH3 123 17 9 3 A 10 > 6 HO Hydrophilic Hydrophobic region region 胆固醇结构式