The cytoskeleton is composed of three types of filaments: microfilaments, intermediate filaments, and microtubules.
The cytoskeleton is a network of protein filaments that provide structural support and enables intracellular support in the eukaryotic cells.
The cytoskeleton helps maintain cell shape and organelles, rapidly assembles and disassembles and has the ability to grow rapid changes in cell shape.
Microtubules are hollow, tubular structures composed of tubuline proteins. They have a diameter of 25nm and is able to provide structural support and serves as tracks for intracellular transport. they resist compression and involved in processes like cell division.
Microtubules also provide motility:
Flagella - "snake like motion'
Cilia - 'rowing like motion'
Microfilaments are actin filaments. They are thin and flexible filaments made up of actin protein subunits arranged in a helical structure. They have a diameter of 7nm and are highly dynamic, constantly assembling and disassembling.
Microfilaments are 3d linear strand of networks using branching proteins.
Microfilaments resist tension and the cortical network under the plasma membrane helps make this region lessfluid, which maintains shape.
The interactions between actin and motor proteins such as myosin support cell movement and allow musclecontraction.
Intermediate filaments is made of proteins including keratin, lamins and neurofilaments in neurons. They have a diameter of 10nm, intermediate between microfilaments and microtubules. the proteins contained provide a mechanical strength and stability to tissues and cells. They are supercoiled into cable and less dynamic than the other two.
Intermediate filaments form permanent cellular structures.
Intermediate filaments are found in epithelial tissue, hair follicles, skin, nails, muscles, nerves, blood vessels, and connective tissue
Cell junctions allow cell-cell adhesion and communication, allowing cells to form tissues and uncoordinated functions.
There are 3 types of cell junctions:
Tight junctions
Desmosomes
Gap junctions
Tight junctions hold adjacent cells together and form a continuous impermeable seal between cells to preventleakage of fluids and solutes through the intracellular space. They regulate a passage of ions, water and small molecules.
Desmosomes provide a strong adhesion between adjacent cells, anchoring intermediate filaments to the cell membrane and transmitting force across tissues. They are connected into the cell by intermediate filaments.
Gap junctions form channels between adjacent cells that allow direct exchange of ions, small signalling molecules, which allow rapid cell-cell communication and at the point of the cytoplasm.
Many tissues lie in the extracellular composition which varies between tissues. This extracellularcomposition is called the matrix and composed of materials secreted by cells.
The secreted cells occurs by constitutive exocytosis. Most ECM proteins are glycoproteins and the most abundant one is collagen.
Collagen have great tensilestrength and embedded into a proteoglycan complex.
Proteoglycan complex are proteins with extensive sugar additions and can trap water within the ECM. This resistscompression and helps retain tissue shape.
Fibronectins attach cells to ECM
Integrins link cytoskeleton to ECM
Fibronectins and Integrins provide communication link from ECM to cell interior