Filaments: Definition & Function

Filaments: Definition & Function
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  • 0:02 What Are Filaments?
  • 0:44 Microtubules
  • 1:41 Intermediate Filaments
  • 2:52 Microfilaments
  • 4:25 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
This lesson is about filaments, the structural proteins of the cell. Here, the structure of the three types of filaments and their functions will be described.

What Are Filaments?

Filaments are the structural proteins of the cell. There are three types of filaments: microtubules, microfilaments (known as actin filaments), and intermediate filaments. Together, these three types of filaments make up the cytoskeleton. Like the name sounds, the cytoskeleton gives the cell support, like a skeleton in a body! Similarly, the cytoskeleton allows the cell to move around its environment, much like our skeleton helps us move.

Other functions include helping with cell division, adhesion between cells, and movement of things within the cell. To learn more about filaments, we'll look at each individual type.

Microtubules

Microtubules are the biggest filaments in the cell. They are made of a protein called tubulin, which are arranged in dimers to make a single long strand. Each dimer, or chemical structure with two like sub-units, is made of one alpha and one beta tubulin. Microtubules originate near the nucleus, at structures called centrioles and radiate outwards towards the edges of the cell.

Microtubules can be thought of as the highway of the cell. Cells transport materials in small bubbles called vesicles, up and down the microtubules. The vesicles act as the trucks driving on the highway. Similar to how highways may undergo construction, microtubules are frequently assembled and disassembled based on where things need to go in the cell.

microtubule

Above is a diagram of two proteins that act like trucks on the microtubule highway. These proteins, dynein and kinesin, move cargo along the microtubules in the cell.

Intermediate Filaments

Intermediate filaments are smaller than microtubules but larger than microfilaments. Intermediate filaments can be made of different proteins, but are all in the same family and share similar characteristics. Examples of intermediate proteins are: desmin, which helps to connect cells to each other in organs like skin; keratin, which makes up hair and nails; and laminin, which is involved in supporting the structure of the nucleus inside cells. Intermediate filaments can assemble into large coils made of many strands of filaments to create stronger chains. In the following image, two intermediate filaments assemble to make a dimer, and two dimers assemble to make a tetramer:

intermediate filament

Intermediate filaments can be thought of as cushioning for the cell. The proteins are easily stretched and can help the cell hold onto other cells during mechanical stress. Think of a professional mountain bike. The bike has shock absorbers connecting the seat to the bike. These keep the seat attached and make it easier for the biker to go over large bumps in the road. Intermediate filaments keep cells attached to each other in a flexible way. In the next image, skin cells are attached together through junctions called desmosomes, which are made of the intermediate filament desmin:

skin

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