Regulation of animal cell shape

• 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 less fluid, which maintains shape.
• The interactions between actin and motor proteins such as myosin support cell movement and allow muscle contraction.
• 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 prevent leakage 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 extracellular composition 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 tensile strength and embedded into a proteoglycan complex.
• Proteoglycan complex are proteins with extensive sugar additions and can trap water within the ECM. This resists compression 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