上游充通大兽 Many Common Features Underlie the Diversity SHANGHAI JIAO TONG UNIVERSITY of Biological Membranes Membranes are as diverse in structure as they are in function.However, they do have in common a number of important attributes: 1.膜是层类结构，只有两个分子厚。Membranes are sheetlike structures, only two molecules thick,that form dosed boundaries between different compartments.The thickness of most membranes is between 60 A(6 nm) and 100 A(10 nm). 2.膜的主要组分是脂质和蛋白质。Membranes consist mainly of lipids and proteins.The mass ratio of lipids to proteins ranges from 1:4 to 4:1. Membranes also contain carbohydrates that are linked to lipids and proteins. 3.膜的脂质分子分为亲水和疏水两个部分。Membrane lipids are small molecules that have both hydrophilic(亲水的)and hydrophobic(疏水 的)moieties.这些脂质分子在水中能够自发形成封闭双层结构。These lipids spontaneously form closed bimolecular sheets in aqueous media. These lipid bilayers are barriers to the flow of polar molecules.Many Common Features Underlie the Diversity of Biological Membranes Membranes are as diverse in structure as they are in function. However, they do have in common a number of important attributes: 1.膜是层类结构，只有两个分子厚。Membranes are sheetlike structures, only two molecules thick, that form dosed boundaries between different compartments. The thickness of most membranes is between 60 Å (6 nm) and 100 Å (10 nm). 2.膜的主要组分是脂质和蛋白质。Membranes consist mainly of lipids and proteins. The mass ratio of lipids to proteins ranges from 1:4 to 4:1. Membranes also contain carbohydrates that are linked to lipids and proteins. 3.膜的脂质分子分为亲水和疏水两个部分。Membrane lipids are small molecules that have both hydrophilic (亲水的) and hydrophobic (疏水 的) moieties.这些脂质分子在水中能够自发形成封闭双层结构。These lipids spontaneously form closed bimolecular sheets in aqueous media. These lipid bilayers are barriers to the flow of polar molecules