cytoskeleton: functions

• microtubules and microfilaments support the cells organelles and keep them in position
• microtubules and microfilaments also help strengthen cell and maintain its shape
• microtubules and microfilaments are also responsible for the movement of materials within the cell. e.g. movement of chromosomes when separating during cell division depends on concentration of microtubules.
• proteins of the cytoskeleton also cause the cell to move

  e.g. the movement of cilia and flagella is caused by

  the cytoskeletal protein filaments that run through them. So

  in single cells that have a flagellum (e.g. sperm cells)

  cytoskeleton propels whole cell.
• label the diagram

  A) golgi apparatus

  B) microubules

  C) microfilaments

  D) mitochondrion

  
• • The cytoskeleton has a number of different functions, including:
  • Maintaining the shape of the cell.
  • Securing some organelles in specific positions.
  • Allowing cytoplasm and vesicles to move within the cell.
  • Enabling cells within multicellular organisms to move.

  Protein fibres of the cytoskeleton
• • There are three types of fibres within the cytoskeleton:
  • Microfilaments thicken the cortex around the inner edge of a cell and, like rubber bands, they resist tension.
  • Intermediate filaments are found throughout the cell and hold organelles in place.
  • Microtubules are found in the interior of the cell where they maintain cell shape by resisting compressive forces.
• • Microfilaments are the narrowest protein fibres in the cytoskeleton (about 7 nm in diameter).
  • They are made of two intertwined strands of a globular protein called actin.
  • Actin works together with a motor protein, called myosin.
  • So, microfilaments are important for cellular events requiring motion (like eukaryotic cell division).
• • Intermediate filaments are made of several strands of fibrous proteins that are wound together.
  • The diameter of intermediate filaments (which is 8-10 nm) is between that of microfilaments and microtubules.
  • Intermediate filaments have no role in cell movement, as their role is purely structural.
  • They bear tension, maintaining the shape of the cell, and anchor the nucleus and other organelles in place.
  • Several types of fibrous proteins are found in the intermediate filaments, such as keratin.
• The cytoskeleton facilitates cell movement by enabling the formation of cellular extensions like cilia and flagella.
• • Microtubules are the widest components of the cytoskeleton (diameter is about 25 nm).
  • They are small hollow tubes, with walls made from polymerised dimers of two globular proteins (α-tubulin and β-tubulin).
  • Like microfilaments, microtubules can disassemble and reform quickly.Functions of microtubules:
  • Help the cell resist compression.
  • Provide a track along which vesicles move through the cell.
  • Pull replicated chromosomes to opposite ends of a dividing cell.
  • Microtubules are the structural elements of flagella, cilia and centrioles.