The Cytoskeleton

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The Cytoskeleton

• Still in Chapter 4

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• The CYTOSKELETON
• Extensive network of protein fibers
• Functions in
• Support provides internal structure to the cell
• Transport of organelles and protein vesicles
• Cell motility
• cilia
• flagella
• psuedopodia

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Cell motility
cilia
flagella
Pseudopodia
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Cytoskeleton

• Three filaments
• Microtubules MTs
• Microfilaments MFs
• Intermediate filaments IFs

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Table 4.1
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Microtubules

• Thickest filaments of the cytoskeleton
• Function in
• Mvmt of chromosomes
• Mvmt of organelles
• Mvmt of cargo (vesicles)
• Cell motility (cilia and flagella)
• Cell shape
• Made of two proteins that form dimers
• a-tubulin
• ß-tubulin

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Microtubules

• Microtubules must be anchored to some part of the
  cell
• Centrosome or Microtubule organizing centers
  (MTOCs)
• basal bodies are important in cilia and flagella
• centrioles are important in cell division
• 9 x 3 structures 9 sets of 3 microtubules

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Mitosis and Microtubule Movement of Chromosomes

• During mitosis, the centrioles anchor the
  formation of microtubules which form the spindle
  on which the chromosomes will attach.

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Cilia and Flagella are made of Microtubules

• Flagella one or a few, long structures
• Cilia many, shorter appendages
• 9 2 arrangement of MTs
• Anchored to the cell by a basal body

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FYI
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Motor Proteins
FYI

• Motor Proteins
• produce movement
• Kinesin
• Dynein
• Are motor proteins associated with microtubules

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Actin Filaments

• Also called Microfilaments
• Functions
• Movement of cells through psuedopodia
• Muscle contraction in multicellular organisms
• Animal cell division
• Cell shape

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Other cell movements driven by microfilaments

• Acrosome reaction when sperm penetrate the egg
  cell

FYI
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Microfilaments

• Made of the protein actin
• The motor protein that works with actin is called
  myosin
• Actin/Myosin work together in muscle tissue
• Muscle contractions!

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• Myosin is an actin motor protein
• Actin Myosin are responsible for muscle
  contraction

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Intermediate Filaments

• IF function is structural to reinforce cells and
  organize them into tissues
• Claws and hair are the dead remnants of epidermal
  cells composed mainly of IF proteins
• Function in the Extra Cellular Matrix to bind
  cells into tissues
• Motility is NOT a function

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Intermediate Filaments

• Up to 50 different proteins/genes that assemble
  into intermediate filaments
• Collagen
• Keratin
• Elastin
• Fibronectin
• Laminin

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Intermediate Filaments are often part of the
Extracellular Matrix
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Fig. 10.2
FYI
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Outside of the Plasma Membrane

• Extracellular Matrix (ECM) is attached to the
  plasma membrane
• Cell-cell recognition
• Contact between cells
• Communication between cells

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The Extracellular Matrix (ECM)

• Made of Proteins, glycolipids, and glycoproteins
  secreted by the cell
• Keratin (finger toe nails)
• Collagen (hair and other things
• Elastin
• Laminin
• Fibronectin

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Holding cells together Junctions Are
Specialized Contacts Between Cells

• Allow cells to form strong connections
• Facilitate or prevent passage of materials
  between cells
• Facilitate communication between cells

• Types of Junctions
• Anchoring Junctions
• Desmosomes
• Tight Junctions
• Gap junctions
• Plasmodesmata

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Desmosomes

• Desmosomes are points of attachment betweencells.
  
• Intermediate filaments anchor the desmosomes in
  cell.

Holding cells together by snaps
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Fig. 10.7

• In desmosomes, cadherins connect cells to each
  other and to intermediate filaments

FYI
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Tight Junctions

• Tight junctions hold cells very tightly together
  solutes cannot pass around cells
• Cells connected by tight junctions seal off body
  cavities
• blood/brain barrier
• spinal fluid/blood
• Pericardial cavity
• Peritoneum

Holding cells together by zippers
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Gap Junctions
Connecting cells by large pipes

• Allow small ions to pass between cells

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Plants, Bacteria, and Fungi have Cell Walls in
addition to the ECM

• Made of carbohydrates
• Plant cell walls cellulose pectin
• wood is made of cell walls of dead cells
• Bacterial cell walls peptidoglycan

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Plasmodesmata

• Instead of Gap Junctions
• Large channels (20-40 nm wide) between plant
  cells
• Allow movement of small molecules across the
  plasma membrane and cell wall

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Fig. 10.15