Final answer:
There are two mechanisms for cellular entry of extracellular viruses and bacteria through the endocytic pathway: effector proteins secreted by the pathogen and surface proteins that bind to host cell receptors.
Step-by-step explanation:
The mechanisms of cellular entry of extracellular viruses and bacteria through the endocytic pathway can occur in different ways depending on the specific pathogen.
One mechanism involves the secretion of effector proteins by the pathogen, which triggers the entry of the pathogen into the host cell. For example, Salmonella and Shigella use this mechanism by secreting effector molecules that cause the formation of membrane ruffles, allowing the bacterial cell to enter the host cell.
Another mechanism relies on surface proteins expressed by the pathogen that bind to receptors on the host cell, leading to entry. Yersinia pseudotuberculosis, for instance, produces a surface protein called invasin that binds to beta-1 integrins on host cells, facilitating entry.