除小的疏水分子外,无蛋白脂质双分子层对大多数分子相对不渗透。极性的、体积大的或带电的分子需要转运蛋白才能穿过质膜。跨膜转运蛋白是蛋白质的质膜,可以大致分为水通道蛋白通道蛋白质,蛋白质载体和水泵(表1),每个运输蛋白质是非常具体和运输货物只有一个类分子,如离子或糖,通常只有一个特定的分子内部类。

表1:膜转运蛋白

包含膜转运蛋白的表格。该表包含传输器类型、传输器子类型和函数的列。第一个运输机:水通道蛋白。没有子类型。功能:与通道蛋白不同,通道蛋白是通过细胞膜运输水的通道,并且始终保持开放状态。下一个转运体类型:通道蛋白。亚型:电压门控,配体门控和机械门控。功能:门控通道的开启和关闭响应配体结合,机械变形,或电压。能够运送极性的、体积大的或带电的分子,这些分子不能沿电化学梯度扩散穿过薄膜。下一个转运体类型:载体蛋白。 Subtypes: uniporter, symporter, anti porter. Function: Protein that binds the cargo on one side of the membrane and undergoes a conformational change to move the cargo to the other side of the membrane. Can transport one type of cargo in one direction, multiple types of cargo simultaneously in the same direction, or multiple cargo types in opposite directions. Can transport polar, bulky, or charged molecules that cannot diffuse through the membrane down the electrochemical gradient. Next transporter type: active transport. Subtypes: ATP driven pump, light driven pump, and coupled transport. Function: Uses energy to transport cargo molecules against the electrochemical gradient. Pumps transport cargo up an electrochemical gradient using energy from ATP or light. Coupled transport uses a molecule travelling down an electrochemical gradient to drag another molecule up the electrochemical gradient. This could be through anti port or symport transport.

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