hello everyone and welcome in this video we will discuss the cytoskeleton and cell motility today we believe that walter fleming was the first to postulate that the problem could be divided into compartments a fiber network the king is an inter fibrillar substance however this theory was set aside to give space to that of Conklin who instead discovered an ordered spatial organization capable of directing the orientation of the future divisions of the zygote and determining the localization of future organs. This suggested that the heterogeneity of the cytoplasm was maintained by a plasma chip scaffold made up of fibrillar elements in the 1960s with the improvement of sample preparation methods and the introduction of the high voltage electron microscope which Porter identified a dense fibrillar structure which they called micro sieve among vehicles today we know that the cytoskeleton is in fact the skeleton of the cell, it is made up of a complex system of protein filaments that give the cell a correct shape and also adequate robustness and appropriate internal structuring is normally a dynamic structure and depending on the case the skeletal gyrus allows the cell to divide, move by crawling for example or notice contracting or extending long cellular extensions there are three components of the cytoskeleton we talk about micro filaments microtubules in intermediate filaments micro filaments are actin polymers with a diameter of about 6 nanometers and a variable length these can perform very different functions in some types of cells they form specialized structures such as the relatively ecstatic support of the micro villi in the entero ct although these filaments are dispersed throughout the cell they are concentrated above all in the strong kes i.e. in the peripheral portion just under the plasma membrane the cortex and therefore a dense weave that performs multiple functions on the one hand excludes and physically the organelles of the most peripheral portion of the cytoplasm, mainly responsible for the dynamics of the transport signaling processes that occur in the cell immediately behind the plasma membrane on the other hand the cortex itself is a structure capable of exhibiting and notable structural variations that allow the movement of the cell edge in processes of cellular locomotion or phagocytosis, microtubules, on the other hand, are long hollow cylinders and composed of the tubulin protein, these have an external diameter of 25 nanometers and are much more rigid than actin filaments, these are long and straight and furthermore they have one end attached to a single microtubule organizing center called the so center but the intermediate filaments instead are more similar to ropes and have an intermediate diameter compared to the previous ones, i.e. approximately 10 nanometers these are composed of proteins of the intermediate filaments which constitute a large and heterogeneous family, one type II intermediate filament forms a network called the nuclear mine which is located just under the internal nuclear membrane others extend through the cytoplasm giving the cells a force mechanically, each type of filament that we have mentioned is made up of smaller protein subunits that are held together by weak covalent interactions. The subunits can diffuse rapidly in the cytoplasm while ready-made and assembled filaments cannot do so for this rapid organizations of the cytoskeleton are obtained by assembling filaments into single subunits in one site and then reassembling them in a different site is an important thing is that the term cytoskeleton can make one think of a static structure when on the contrary it is a highly dynamic structure because it implies for manifestation of phenomena such as the locomotion of the vesicular graph or other morphological changes which overall are called cellular motility to better understand what the functions of these structures are and the ways in which they are carried out in the cell it is necessary to describe the main molecular characteristics of actin and other proteins Latin is one of the most abundant proteins in the cell arriving on average to represent up to 15 percent of the total protein content, numerical actinamo is a globular protein with a weight of approximately 42 kg daltons and a diameter of around 5.4 nanometers. the monomer is characterized by a binding site and hydrolysis of ATP so that the protein can be in various states actin monomers can combine to form polymers made up of two filaments wrapped in a single right-handed helix called f actin a fundamental characteristic of micro f tina filaments is their intensity polarity with one end differing both chemically and structurally from the other but in addition to the structural polarity with its implications we must consider another parameter of great importance namely the polymerization dynamics and it is polymerization of the filaments starting from a high concentration of free monomers in solution and by measuring the formation of the polymer a lag phase is observed followed by a growth phase the lag phase and by the fact that the association of two monomers to form a very low probability dimer even lower than that of dissociation of the dimer into the two even monas, consequently in order for the polymerization to start it is necessary at least the formation of a three mer which is more stable than the devero itri mary then they lengthen due to the addition of new subunits the elongation in fact it involves the addition of new monomers from both ends of the polymerization nuclei and is the fastest phase and then the last stage called a in the link in which various short filaments bind together to obviously form polymers of longer length this entire polymerization process is aided by a very fine regulation of numerous accessory proteins that we will surely find later and which can be the profiles na lane tubina too much myosin alpha khtey nina fila mina fibrin and many others regarding the dynamics of cooking these are the basis of cellular motility processes in which the polymerization of the cell constitutes the propulsive force for the movement these mechanisms are mostly implemented in the movement processes a me boyd and and in the protrusion of cellular extrusions such as cody thread and pseudo podia in the movement me boyd is in fact an adherent cell a substrate can move a coordinated series of events the cell in movement is polarized and shows an anterior side which is characterized by the dynamics of external flexion and advancement of the membrane and a posterior side characterized instead by retraction dynamics. Let's now talk about microtubules. Microtubules are the largest cytoskeletal elements and are made up of tubulin which, as Latin, is a globular protein that tends to polymerize into structures called proto filaments and the constituent unit of these lamenting products is a hetero of mere as far as your bowline is concerned we know that there are three types of tube lines the alpha beta or gamma alpha and beta they bind to form the basic entity which is called free hetero for the construction of the proto filament and the affinity between alpha tubulin and beta tubulin is high so much so that in the cytoplasm only mary heteros are observed and not of monomers therefore each single filament is made up of a sequence of alpha and beta line tubes alternating with each other and the proto filaments and microtubules are therefore hetero polymers the lament products interact laterally with each other and form a planar structure which closes to form a cylinder cable or a microtubule in different conditions in vitro microtubules can form which are made up of a variable number of protons ranging from 8 to 16 we know that in the cell the microtubules are made up of 13 filaments and form a hollow cylinder with an internal diameter of about 25 nanometers the microtubule is therefore a rigid, helical hollow tube made up of 13 filaments aligned in parallel at the most dynamic end the growth and shortening are faster and is called the plus end and corresponds to the end exposing the beta sub unit while the other is called the minus end and corresponds to the alpha subunit at the two ends we know that the dynamic events are different they have a difference linked to the speed in the plus subunit tubulin can be removed or added faster than its unit minus the polymerization of microtubules originates from complexes that in the cell are all located in correspondence with a thickening of protein material that surrounds the oil centers and which takes the name of material for the ular centers. The set of oil centers of the material for the lar centers constitutes the center soma and for the function of these complexes it is therefore called the center of organization of microtubules the center so but as center of organization of microtubules dictates the geometry of this component of the cytoskeleton inside the cell in fact all the microtubules start from the center of the cell towards which their minus end is facing and radiate towards the periphery where their plus end is facing. It is important to remember these two ends for the role that the motor proteins which we are going to talk about now will have, in fact the radial distribution of the microtubules and their very precise polarity within the cell have a fundamental role in giving directionality to certain transport processes that must take place from the center towards the periphery or from the periphery towards the center, in fact there are motor proteins that move by sliding on the microtubules and the main ones are the Chinese ones which move unidirectionally towards the plus end and the Divine ones which instead move towards the minus end. The directionality of the movement if microtubules is the cornerstone of the vesicle transport processes which occur in both directions between the endoplasmic reticulum and the Golgi apparatus and between the latter and the plasma membrane. Not to be forgotten is the role of some proteins that associate with the microtubules to stabilize the structure called maps within the cell is an organ it consists of an ordered structure in the microtubules the center which forms a cylinder with a length of about 0.5 micrometers and a diameter of 0.2 micrometers the microtubules of the center are oriented along the main axis of the center there are 9 triple reads arranged in the triplet my future closest to the center is a classic microtubule made up of 13 lawn filaments while the other two are not complete cylinders but are made up of 10 lawn filaments that go to close on the adjacent microtubule regarding the structure of the oil centers and their role within the cell cycle we will delve deeper in the next videos so I advise you to write to yourself if you don't want to get lost there it is important to know that microtubules also come into play in other structures which are the cilia and flagella but we will also deal with this in detail in a next video regarding cell motility. Let's now focus on the intermediate filaments. Even the intermediate filaments are protein polymers but typically do not show the dynamics that we have described regarding the micro filaments and micro tovoli but they form very stable structures in the cell which are aimed at providing mechanical resistance to deformations and external stresses. The intermediate filaments are therefore abundant in cells subjected to strong mechanical stresses and some organisms equipped with exoskeleton the intermediate filaments are distinguished based on their localization in the nuclear cytoplasm the intermediate filaments in the cytoplasm are divided into mint keratins the neuro filaments the cretins are typical of the epithelia and belong to two classes of intermediate filaments, class 1 of the acid keratins and the class 2 of neutral vessel keratins whereas the intermediate filaments of the connective tissue of the muscle and glial cells belong to the class of 5th mint while in the neurons they are found the intermediate filaments of class four also known as neuro filaments, finally the nuclear intermediate filaments belong to class 5 or the laminae and are found in the nuclear lamina and in the skeleton nucleus where they constitute a mechanical support network for the structure of the nucleus and an anchor for the chromatin but as the intermediate filaments are formed all the proteins of the films intermediate bodies are low ancellar reform and present an extended central domain which is narrow and long due to the folding of the alpha helix of the protein the central region of the double alpha helix is where it exceeds times it is also called qohelet coil during the assembly of the polymer the dimer is formed by the coiling of two molecules proteins that interact laterally through their respective central domains forming the structure called coil and coil as regards the formation of the tetra america structure both by wrapping 2 of mary in a staggered way i.e. in reverse it is in the head-to-tail position different tetra mary always join together in a staggered to form proto filaments and different product filaments then associate with each other thanks to lateral hydrophobic interactions of the coil and coil domains which provide mechanical resistance to the filament, all the peptides that participate in the construction of the filaments are phosphors given by different kinases since phosphorylation is a mechanism for regulating the assembly while the destruction of the filaments that need to be replaced is entrusted to proteolysis, obviously the intermediate filaments are also characterized by accessory proteins, that is, there are proteins whose function is to connect the different components of the skeletal structure to each other, creating a mechanical unit between them, therefore given the different mechanical properties of the three classes of polymers of the cytoskeleton, the formation of a single network that connects them through protein bridges allows to confer to the cell with its structural self-support characteristics which are elasticity and flexibility so that following a deformation due to pressure or stretching within certain limits the cell is able to return to its original shape with this we have concluded the chapter on the cytoskeleton will follow an in-depth video regarding the transport and locomotion processes that use micro filaments and microtubules as tracks and we will deal in detail with my hosein and Chinese ne and dinelli, having said that that's all for today thanks for your attention and see you soon