Exocytosis is a form of bulk transport during which large numbers of molecules are transported out of the cell. In exocytosis, a vesicle (a small, membrane-bound compartment) containing the molecules to be released fuses with the cell membrane, and the contents of the vesicle are expelled. Exocytosis is important for the transport of neurotransmitters.
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- So this adds a patch of membrane to the cell's outer membrane. But that would mean that the cell's membrane keeps getting bigger and bigger with each exocytosis. Does it get bigger? And if not, why doesn't it?(19 votes)
- It does add to the membrane, but while exocytosis is occurring, so is endocytosis. Endocytosis is basically the opposite, where the membrane makes a pit on the outside surface of the cell and pulls in molecules, forming a vesicle. Endocytosis is cell drinking (pinocytosis) and cell eating (phagocytosis).(27 votes)
- This would mean that the golgi apparatus is also phospholipid bilayer, right?(7 votes)
- The golgi apparatus is enclosed by a phospholipid bilayer, as well as all organelles within in the cell (excluding ribosomes).(2 votes)
- Is the release of neurotransmitters, a kind of exocytosis?(6 votes)
- Yes, it is. During the release of neurotransmitter vesicles merge with the Outer cell membrane(7 votes)
- sal is nearly eating that microphone dawg(8 votes)
- If the vesicles are made of the same bilayer as the membrane, aren't the charged parts of the phospholipids of the vesicle repelled by the (same) charged parts of the membrane (same charge repel eachother)? Or does this work via proteins on the membrane? if yes, how do they work?(5 votes)
- No, cell organelles (even though membrane-bound) do not repel each other when close to the cell membrane. Why? First of all, the different charge is on the cytoplasmic side of the cell membrane than on the outer side.
Inside of cell is a certain charge which is okay for cell organelles. While on the outside is a different charge.
This is what helps exocytosis.
If you ask for endocytosis. well, there are carbohydrates which are positively charged on the surface and modify charge.
The reason why endocytosis and exocytosis is possible - is exactly the chemical charge and chemical constituents of the membrane (surrounding vesicles).(1 vote)
- When the protein is expelled from the cell, sal says that it goes somewhere else to be used. How does the protein know where to go(4 votes)
- Chemical signaling present in the cell and between cells helps the movement of proteins. Vesicles always know where to go, and where they will be uptaken. Signaling molecules which go further+sta re hormones which are distributed via blood - in that case, blood flow (created by pumping of the heart) directs hormones, and after that when they reach target destination, target cells usually have receptors which bind hormones. After binding, changes occur.(1 vote)
- how long does it take for this prosses to happen?(3 votes)
- On the order of minutes — the paper I looked at claimed 90-120 seconds for regulated exocytosis in Drosophila (fruit flies).
- How does your body create phospholipid bilayers? Are they naturally occurring in the foods we eat, so our cells just 'steal' them off of consumed plant cells? Or does our body have to piece them together? There seems to be large and important quantities of them in cells.(2 votes)
- Great question!
The membranes of living cells are constantly having new lipids and proteins added. Some organelle membranes like the ER and nuclear envelope can breakdown into small vesicles and then reform, others like mitochondria are always present.
Membranes as structures appear to be inherited separately from genes§, though their specific composition is controlled by genes.
While our bodies don't incorporate whole membranes from food, we do absorb many lipids from food (some of which are essential components of our diet) and use them to maintain and grow cellular membranes.
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References and further reading:
§Note: This is known as structural inheritance — for an introduction see:
- It looks to me like energy is being used in endocytosis and exocytosis. Are endocytosis and exocytosis forms of bulk transport, or are they active transport? Is bulk transport the same thing as active transport?(2 votes)
- Don't quote me on this, but I'm pretty sure that bulk transport is a form of active transport.(2 votes)
- regarding3:20to3:40If moter proteins must use ATP to move the vesicles along tracks how can they possibly use it efficiently enough to justify using 1 atp to carry 1 Amino acid at a time for a mere hundredth perhaps worse of a protein that can bring in sugar for processing.(2 votes)
- well they can, they are designed to be efficient and utilize as much as possible energy and to waste at least as possible energy (since we know all work requires some waste of energy).(1 vote)
- Let's talk a little bit about exocytosis, which is how the cell is able to release larger molecules that might be used by the rest of the body. Other cells, or maybe it's going to be part of the extracellular matrix. And to understand how this works, it's really the reverse of endocytosis, we're going to go and produce some proteins in the endoplasmic reticulum, this is our classic example. Those proteins are then going to bud off, in their own little vesicles, which then merge with the golgi apparatus where they are further processed. So they're processed in the golgi apparatus, right over here, and then eventually they're going to bud off of the golgi apparatus in new vesicles, and those vesicles are going to make their way over to the cell's outer membrane, the plasma membrane and the membranes of the vesicles are going to merge with the membrane of the cell and in doing so, they're going to release their contents. And this is classic exocytosis, there are other cases where maybe it merges partially, releases the contents and then buds back is called the "kiss and run" method of exocytosis, but the classic one is it merges with the membrane. We can look at this, this membrane after the vesicle's membrane has merged with the plasma membrane, the membrane might look like this. So if the vesicle, let me do the vesicle's membrane in orange, if the vesicle's membrane is at an orange, well now it has merged like this and it has released its contents. It has released the protein to be used someplace else, someplace else in the body. And I want to be clear, this membrane, and I talk about it many times in many other videos, even though I've drawn it as one line right over here, this is going to be a phospholipid bilayer, so if we were to zoom in, it would look like this. It's a phospholipid bilayer. So these are some of the phospholipids that were part of the original part of the original membrane and then we also, in my little box, I get some of the ones that are part of, or that were part of the vesicle that was holding that protein. That were part of the vesicle that was holding the protein. So I really want to stress I want to really stress these lines that I'm drawing these are bilayers of phospholilpids. And all of these lines, these membranes that you see, these are all bilayers of phospholipids. Just to make sure that we are visualizing this correct. And that's what exocytosis is and one thing that I find interesting is when you first learn about it you see it diagrammed like this and you just assume, okay, well, these bubbles of these with these membranes they just randomly must float eventually to the membrane where they get merged and then they release their contents. But actually it isn't that chaotic. They actually can sit on tracks so they actually can sit on tracks. Remember we talked about the cytoskeleton which isn't drawn enough probably because it makes drawings really messy but whenever we think about a cell there's all this structure to it. There's all this structure to it, microtubules, microfilaments, intermediate filaments, all of these things over here that not only provide structure to the cell, but they can be used to transport. And these vesicles these vesicles can actually ride on these structures and you could actually have motor proteins that are using ATP to actively push the vesicle containing its contents so this is a kind of transportation. It's really like a factory to push them towards the membrane so that they can be released. So whenever I think about it, it's fascinating 'cause I always talk about these cells being a universe unto themselves. And they aren't just these blobs, they have all of these structures, there's all of these proteins that are really on an unbelievably small scale able to do these fairly intricate processes. So what I just showed you, once again, this is classic exocytosis, you'll see it when you have proteins, lipids, being produced by the cell that need to be released somehow. They're also famously used in neurons, the chemical signal, when you go from one neuron to another, you have exocytosis of neurotransmitters that will trigger the next neuron. So these are very, very important processes. Our bodies would not function properly or, wouldn't function at all, if we did not have exocytosis.