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Course: Biology library > Unit 10
Lesson 5: Bulk transportEndocytosis, phagocytosis, and pinocytosis
Phagocytosis is the process by which a cell engulfs and internalizes a large particle, such as a bacterium, by extending its membrane around it. Pinocytosis is similar, but instead the cell engulfs droplets of extracellular fluid, taking in any dissolved substances within. Both phagocytosis and pinocytosis are forms of endocytosis.
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Why would the cell want to "consume" anything?(12 votes)
The ability to internalize material from outside the cell is important for several cellular processes including the ingestion of essential nutrients, removal of dead or damaged cells from the body, and defense against microorganisms. Eukaryotic cells internalize fluid, large and small molecules, and even other cells from their surroundings by a process called endocytosis. During endocytosis, the plasma membrane of the cell forms a pocket around the material to be internalized. The pocket closes and then separates from the plasma membrane.
In phagocytosis, a type of endocytosis, large vesicles ingest whole microorganisms.
inside surface of the plasma membrane to form a membrane-enclosed bubble, or vesicle, containing the ingested material. There are two main types of endocytosis that are distinguished by the size of the vesicle formed and the cellular machinery involved. Pinocytosis (cell drinking) describes the internalization of extracellular fluid and small macromolecules by means of small vesicles. Phagocytosis (cell eating) describes the ingestion of large particles such as cell debris and whole microorganisms by means of large vesicles. While all eukaryotic cells are continually ingesting fluid and molecules by pinocytosis, only specialized phagocytic cells ingest large particles.
Read more: http://www.biologyreference.com/Dn-Ep/Endocytosis.html#ixzz3wrmmIMYU(26 votes)
can a cell eat a cell?(9 votes)
Yes! Certain cells specialize in doing this, Like Phagocytes and Macrophages. It can be necessary to do such things because sometimes a cell becomes toxic or damaged, and needs to be destroyed.(23 votes)
Is the food vacuole from phagocytosis also considered a vesicle?(13 votes)
I think so. I also think that cells like bacteria actually put a membrane around themselves that came from a different cell so that other cells will accept it, thinking it is something that they should take in.(6 votes)
What is a cytoskeleton? Thanks(4 votes)
The cytoskeleton is the fibrous web of microtubules and filaments that provide the cell with its structure and shape.(13 votes)
- What is the difference between a vesicle and a vacuole?(4 votes)
The vesicles could be send to everywhere in the cell and also help the cell to send some substance to the outside by exocytosis.
The vacuole is a very big membranous organelle that can help maintain the cell volume, cell structure and concentration in the cell.(16 votes)
Endocytosis is both Phagocytosis and Pinocytosis?(3 votes)
It is more like phagocytosis and pinocytosis are types of endocytosis.
Endocytosis is when a cell takes something into itself, whether that is a virus, ions, glucose molecules, or anything else. But sometimes when a cell takes in a specific thing it is given a special name, that is where pinocytosis and phagocytosis come in.
Pinocytosis is when a cell takes in some kind of liquid, like water. Since it is taking in something (a liquid), it is a special type of endocytosis.
Phagocytosis is when a cell takes in a large particle, like a bacterium. Again, this is a special type of endocytosis.(8 votes)
What's the difference between phagocytosis and pinocytosis?(3 votes)
Phagocytosis--Large particles are engulfed by the cell.
Pinocytosis--Liquids are engulfed by the cell.
The process in which the cell engulfs the substances are the same; the materials are collected in vesicles to be transported into the cell. However, one is used for gathering large particles, and the other is used for fluids.
To remember this difference, notice the prefixes "phago" and "pino". "Phago" is Greek for "to eat". "Pino" is Greek for "to drink".
Does this help?(5 votes)
- How does a cell know when to "eat". Are their receptors involved?(4 votes)
- Some of the time receptors will be involved.
There is a wikipedia article on the multiple types of endocytosis with a bit about their regulation:
https://en.wikipedia.org/wiki/Endocytosis
And, if you want to learn more this recent review may be helpful:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4880020/(3 votes)
- Is endocytosis fully active transport? Does it count as active transport, What if it works by the concentration gradient?(3 votes)
endocytosis requires energy to engulf an object which is why it is counted as active transport(4 votes)
- Won't some part of the membrane be lost, due to the pinch off(4 votes)
Part of the cell membrane is being pinched off in endocytosis, but during exocytosis there is a cell membrane gain, so it would equal out.(2 votes)
Video transcript
- [Voiceover] We have other videos where we talk about how small molecules, or ions, might be able to go through a cell's membrane in different ways, whether actively or passively, maybe facilitated in some way. What we wanna talk about in this video is how we can do this for larger things. We're gonna focus on here is bulk, bulk transport. Transport. So this first example, you could imagine this cell with this mauve or purple-colored membrane is engulfing this big green thing which is maybe a bacteria or something. And so you see that the membrane... Let me make it very clear. This is inside. This is inside the cell. This is outside. Outside the cell. And you can see the cellular membrane starts to wrap around this, I guess we can think of this a bacteria, then it fully wraps around and then that membrane that was wrapping around the bacteria pinches off and now the bacteria is inside of the cell, and it's wrapped by this membrane. And this process where you're engulfing these large things, we call this Phagocytosis. So this is phago... Phagocytosis. And the prefix I guess you'd say, phago comes from the Greek for "to eat". So this is literally about cell eating. And in many cases, this thing that is now in here, you could view this as the cell's food, this compartment that is holding this, in this case bacteria, is gonna transport it maybe to a lysosome, so it can be processed and digested in some way. We would call this big compartment, this membrane-bound compartment, we would call this a food vacuole. Food. Food vacuole. Now this scenario down here is similar but different. Over here I have the cell which is I see part of its membrane and it's in magenta right over here. We can see The Phospholipid Bilayer . That's why I drew two lines for the membrane. And instead of engulfing a large particle or bacteria, it's just engulfing some fluid. It's engulfing some fluid, so you see it's starting to wrap around this section of fluid, wraps even more around this section of fluid, and then the membrane that was around it completely pinches off and goes into the cell. And I'm drawing all of these things in two dimension, but this would actually be happening in three dimension. So this wouldn't just be a circle, this would right over here would be a sphere. And this thing that has been pinched off and is now inside the cell, we call this a vesicle, which is just a general term for these membrane-bound compartments inside of cells. And this process where the cell has essentially drunk a bunch of fluid and the stuff that happens to be in the fluid, we call this Pinocytosis. Pinocytosis. Pinocytosis. And pino comes from the Greek word "to drink". And I'm always fascinated by word roots. And I'm not a linguistic expert here, but it's neat because even in languages I'm familiar with like Hindi and Urdu, the word pina means "to drink", so maybe it's even related to the word pani which is in those words in those languages. I know all of these have a shared linguistic root, so it's always fascinating to see these linguistic connections. So this is Pinocytosis where the cell is drinking so to speak, but it's also getting the other stuff that's in that fluid. This is Phagocytosis, the cell is eating. And these are both special cases of I guess the more general term of engulfing in this way which is called Endocytosis. Endocytosis. So Phagocytosis is a form of Endocytosis, and Pinocytosis is a form of Endocytosis. Now the next question you might say is: OK I can get that this happens, this can be observed under a microscope, but how does it happen? How does the cell wrap around and pinch around? And like I say in a lot of videos, people think that we understand some of it, but this is not fully fully understood. There is views that well the cytoskeleton must be involved in some way. It has to create space here for this thing to be able to pinch off and move in that direction. It maybe will help actually the cell's membrane wrap around in some way, but these are all areas of active research. How does this Endocytosis actually occur? How does the cell know what to consume I guess you could say, and then how does the membrane actually behave in this way to do it, to do it well?