CYTOSKELETON & PLASMODESMATA

• The cytoskeleton is composed of three molecular structures known as microtubules, microfilaments, and intermediate filaments
• Vesicles ride the cytoskeleton
• The cytoskeleton interacts with motor proteins to produce cell motility
• Microtubules are composed of polymers of the protein tubulin
• Microtubules are hollow tubes made up of twirled alpha and beta tubulin
• In terms of size of cytoskeleton components, microtubules > intermediate filaments > microfilaments
• Microtubules assist with the maintenance of cell shape and movement found in cilia and flagella
• Microfilaments are two intertwined strands of actin
• Microfilaments assist with muscle contraction of animals, cytoplasmic streaming, cell motility, and division of animal cells
• Cytoplasmic streaming is the movement of chloroplasts
• Intermediate filaments are coiled
• Intermediate filaments maintain cell shape, anchor nucleus and certain other organelles, and form the nuclear lamina
• Centrosomes are present in plants to form microtubules
• Each centrosome has a pair of centrioles
• Centrioles are composed of nine triplets of microtubules arranged in a ring
• Centrioles are better observed in animal cells
• Cilia and flagella are groups of microtubules sheathed by an extension of the plasma membrane
• Cilia are short and hair-like, with a stroke-like movement
• Flagella have an undulating beating pattern
• A basal body anchors cilium/flagellum
• The motor protein for cilia and flagella is dynein
• Movements of the dynein feet cause microtubules to bend, rather than slide, because the microtubules are held in place
• Microfilament bundles make up the core of microvilli of intestinal cells
• Microfilaments are responsible for cytoplasmic streaming
• Cytoplasmic streaming is the circular flow of cytoplasm within cells, drivin by actin-myosin interactions
• Microfilaments also contain myosin
• Microfilaments support the cell's shape
• Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes
• Intermediate filaments support cell shape and anchor organelles in place
• Prokaryotes, fungi, and some unicellular eukaryotes have cell walls
• The cell wall protects plants and maintains its shape as well as prevents excessive uptake of water
• Cell walls are made of cellulose fibers embedded in other polysaccharides and protein
• The cell wall consists of

  • Primary cell wall
  • Middle lamellae
  • Secondary cell wall
• The primary cell wall is the outer layer and is relatively thin and flexible
• The middle lamellae is the thin layer between primary walls of adjacent cells
• The secondary cell wall is added between the plasma membrane and the primary cell wall
• The secondary cell wall is only present is some cells
• Plasmodesmata are channels that perforate plant cell walls
• Plasmodesmata allow cells to communicate with each other
• Water and small solutes (and sometimes proteins and RNA) can pass from cell to cell with the help of plasmodesmata