Endocytosis Explained: Receptors & How They Work

[discombobulated]

I need an explanation please!
I understand that endocytosis is when the cell takes in extracellular material and small internal vesicles called endosomes are formed. The endosomes are then sorted according to their contents,(by the golgi apparatus) to go to different cellular destinations like lysosomes.
But, what I'm having trouble understanding is how the receptors fit in. My textbook says this: "Endocytosis is a selective process, controlled by receptors on the cell surface that recognise and bind chemical signals on extracellular molecules or particles." I don't get what it means by, bind chemical signals!
Can someone please explain to me how the receptors are involved in endocytosis, any diagrams or pictures would also be useful because i find it easier to understand things if i can visualise them!
Thanks in advance.

 

[Moonbear]

Part of the trouble is that it's actually a very complicated process, and it's probably far too soon in your biology class to start explaining it all, so you're getting the very simplified version now.

When they say "bind chemical signals," it means other chemicals from outside the cells (they can be secreted from nearby cells, or arriving from blood circulation, for example) that have a structure that is complementary to the receptor can bind to the receptor. When this outside chemical (such as a protein) binds to the receptor, it changes the shape of the receptor a little bit. This in turn changes how it reacts to other molecules in the cell, and a "cell signalling" cascade of events occurs. This cascade of events can be very complicated, so it is best left for more in-depth learning in advanced biology classes, such as molecular and cell biology. So, for now, what you'll need to know is that there is a complicated series of chemical reactions that happens after an outside molecule binds to a receptor that leads to endocytosis, as well as the other actions of that receptor in the cell (it's not just endocytosis), and if you continue learning biology in more advanced courses, I promise you'll learn more than you ever dreamt you could about the details of how this happens.

 

[discombobulated]

Thanks so, the receptors on the cell surface detect the chemicals from the outside body and changes accordingly. Another sentence I'm unclear about is: "the lower pH in endosomes causes the dissociation of mant receptors and their cargoes, enabling them to be directed to different destinations." Does this mean that the receptors are also in the vesicle when the endosome is formed?

 

[Moonbear]

Thanks so, the receptors on the cell surface detect the chemicals from the outside body and changes accordingly.

Not necessarily from outside the body (though sometimes that is true, such as with scents), but from outside the cell with a particular receptor. So, for example, a cell in the pancreas has a receptor to detect glucose in the blood to signal for the cell to make insulin. The cell might also have receptors for insulin so that when enough insulin is made, it gets that message and slows down production.

Another sentence I'm unclear about is: "the lower pH in endosomes causes the dissociation of mant receptors and their cargoes, enabling them to be directed to different destinations." Does this mean that the receptors are also in the vesicle when the endosome is formed?

Yes; this is not always true, but often, yes, the receptor is internalized in the endosome too.