S226; lipid composition influences membrane fluidity: unsaturated fatty acid tails are kinked, limit close packing of the hydrophobic tails and so increase fluidity.

• 胆固醇：1）胆固醇存在于真核细胞膜上（30%25以下），细菌质膜不含有胆固醇，但某些细菌的膜脂中含有甘油脂等中性脂类。