21 弹性蛋白富含甘氨酸和脯氨酸，但是羟脯氨酸很少，没有羟赖氨酸的存在。通过赖氨酸残基共价交联，形成疏松而富有弹性的交联网络。 Elastin functions in connective tissue together with collagen. Whereas elastin provides elasticity, collagen provides rigidity to connective tissue.
32 透明质酸（hyaluronic acid）：is unique among the GAGs in that it does not contain any sulfate.
33 Hyaluronic acid polymers are very large (with molecular weights of 100,000) and can hold a large volume of water. This property makes them excellent lubricators and shock absorbers.促进细胞的增殖和迁徙，调节细胞分化。
34 蛋白聚糖Proteoglycans： The majority of GAGs in the body are linked to core proteins, forming proteoglycans.
35 在高尔基复合体中核心蛋白质的丝氨酸残基（常有Ser-Gly-X-Gly序列）装配上氨基聚糖（GAG）链。 The GAGs extend perpendicularly from the core in a brush-like structure.
64 Transport is specific.There is a maximum transport rate which is achieved when the concentration gradient is very large and each transport protein is working at its maximal rate.The rate of facilitated diffusion is faster than simple diffusion.