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Microfilaments and intermediate filaments

Created by Efrat Bruck.

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  • old spice man green style avatar for user Jess
    At , an example of how microfilaments are used in mitotic division is given but it is not clear what role they play. How do the microfilaments aid in mitotic division? Or what is another example for how the microfilaments are used in human/animal cells?
    (6 votes)
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  • blobby green style avatar for user wuzy
    @, what does she mean by gross movement of the cell?
    (6 votes)
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  • blobby green style avatar for user Jacqueline Rivera Calvillo
    What is the cell lining the small intestine?
    (1 vote)
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  • blobby green style avatar for user Mark Falina
    At it is said microtubules help an amoeba move its pseudopods around a piece of food. Is this how phagocytes (e.g. macrophages) engulf pathogens?
    (1 vote)
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  • duskpin tree style avatar for user jglass20
    Intermediate filaments are described as "permament". If they act in the same way that a spring does, doesn't that mean that they have to be able to move??
    (1 vote)
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  • piceratops seed style avatar for user Lamont
    ntestinal epithelium; simple epithelial cells
    (1 vote)
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  • duskpin ultimate style avatar for user KnowledgeHideout
    Since microfilaments are dynamic, does actin actually shrink during muscle contraction? I thought actin thin filaments just move relative to myosin, increasing the amount of actin-myosin overlap (the I-band and H-zone shorten, while the A-band stays the same length). Also, why isn't myosin classified as a microfilament if it's a thick filament?
    (1 vote)
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  • male robot hal style avatar for user Doğu Yorulmaz
    but a spring is flexible, are intermediate filaments too?
    (1 vote)
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  • leaf green style avatar for user christie2taylor
    Since microfilaments are dynamic, does actin actually shrink during muscle contraction? I thought actin thin filaments just move relative to myosin, increasing the amount of actin-myosin overlap (the I-band and H-zone shorten, while the A-band stays the same length). Also, why isn't myosin classified as a microfilament if it's a thick filament?
    (1 vote)
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  • mr pants teal style avatar for user Shameen Ferdinando
    c'mon u teach well but why don't u throw a joke here and there from time to time like khan
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Video transcript

- [Voiceover] Microfilaments are found in the cytoplasm and they are composed of a protein known as actin, and many molecules of actin will join together to form an actin polymer. And then the actin polymers will twist around each other to form an actin filament. Microfilaments are mainly involved in the gross movement of the cell. And microfilaments are dynamic, and what we mean by that is that they can lengthen and shorten very frequently, and in that sense, they're similar to microtubules. So, they become longer in a process known as actin polymerization, and they become shorter in a process known as actin depolymerization. And it's the polymerization and depolymerization that helps to move the cell. So, one example of where microfilaments help with the gross movement of the cell is during cell division. So the cell at some point is going to be pinched in that way and then eventually it'll separate into two separate cells, and the microfilaments help the cell make that kind of pinched shape, and then move to create two separate cells. Another example of where microfilaments help with the movement of a cell is in an amoeba. So let's say here is our amoeba cell, and we're gonna say that it's trying to capture this piece of food right over here. So in order for it to do that, it has to extend its pseudopods in that direction, and move it around that food molecule. And what helps those pseudopods move? The microfilaments. Let's move on to intermediate filaments. So, intermediate filaments, in contrast to microtubules and microfilaments, are made up of many different types of proteins that are strung together into polymers. These polymers twist together to make the intermediate filaments. And intermediate filaments are different than microtubules and microfilaments in that they're pretty much permanent. So, once they're made by the cell, they kind of stay put, as opposed to microtubules... I'm just gonna abbreviate like that... and microfilaments that we explained are dynamic. They constantly change depending on the needs of the cell. So, what do intermediate filaments do? Well, they provide structural support for the cell. Or another way to say this is they resist mechanical stress. And in the picture it almost looks like the intermediate filaments are this supporting wire, and if you recall in our introduction to cytoskeleton, we mentioned that the intermediate filaments can be compared to the springs inside of a mattress. So, if you were to sit down on a mattress, you might squish it a little bit, but once you stand up, the mattress will revert to its original shape, thanks to the springs inside. So the intermediate filaments, in blue in this picture, act in the same way.