生物膜可以形成一个严密的屏障以阻止离子被动扩散出细胞,而较大的物质例如蛋白质却可以自由穿过膜。包膜病毒感染细胞时,核衣壳可以大部分完整地进入宿主细胞,新的病毒体亦可完好地离开细胞。许多病毒并不裂解宿主细胞,而是使其不断释放感染性子代病毒。例如丝状噬菌体f1就是在其感染的细菌中不断增殖并释放出来,这是由于噬菌体编码的非结构蛋白pⅣ在细菌外膜形 Biofilms can form a tight barrier to stop the passive diffusion of ions out of the cell, while larger substances such as proteins are free to pass through the membrane. When enveloped virus infects cells, the nucleocapsid can enter most of the host cells intact, and new virions can leave the cells intact. Many viruses do not lyse the host cells, but keep releasing the infectious progeny virus. For example, the filamentous bacteriophage f1 is constantly proliferating and releasing in the bacteria it infects, due to the fact that the bacteriophage-encoded nonstructural protein pIV is localized in the bacterial outer membrane