Hi,

I just watched https://www.youtube.com/watch?v=qasm7Mj7CYg on endo and exocytosis mechanisms.

Much of the content in the video is wrong. I study endocytosis and teach it to graduate students at the University of Maryland School of Medicine, and I will warn my students not to watch this. The errors in the video are not just mild or trivial nitpicking errors, but serious, fundamental errors in the topic area. These are mistakes that would cause med students to miss many questions on their exams and cause high school and college students to fail their exams on this topic, because they would show a total misunderstanding of the topic. It should be removed from circulation as soon as possible.

I posted these comments on Youtube also:

Just thinking about the first 3 or so minutes where it discusses endocytosis:

1) Receptor-mediated endocytosis is NOT the fusion of vesicles with cells. It's extremely rare for most cells to take up anything that is membrane-bound. When that happens, e.g. in neutrophils, it is called phagocytosis. Receptor-mediated endocytosis is called RECEPTOR-MEDIATED because receptors on the cell surface recognize extracellular molecules, generally proteins but also viruses or some other things, and the binding of the molecule to the receptor allows the cell to internalize the receptor and the molecule along with it. Receptor-mediated endocytosis involves an inward invagination of the plasma membrane and the creation of a vesicle INSIDE the cell (called an endosome)--almost exactly the opposite of what is shown here.

2) Pinocytosis is NOT an active, directed gobbling of ions or amino acids. Ions like Na or Cl have many routes into the cell, most notably ion channels or transporter molecules, that are constantly active and maintaining ionic homeostasis. Pinocytosis is poorly understood, but much of what is said here about it is wrong. Salmonella does NOT enter the cell via pinocytosis. In fact, the process is triggered by the Salmonella itself, and much more closely resembles phagocytosis; the Salmonella does not passively enter the cell by hitching a ride on an ongoing process.

3) After phagocytosis, the cell does NOT "direct enzymes" to digest internalized pathogens. The phagosome fuses with lysosomes.