L41: The Cytoskeleton & Cell-Cell junctions

• What are actin filaments made of?

  Non-covalent polymers of actin monomers
• What happens to ATP when actin monomers bind in the filament?

  ATP is replaced by ADP
• What is the structure of an actin molecule?

  Two filaments twist around each other
• What are the two ends of an actin filament called?

  Plus (+) end and minus (-) end
• What are the two forms of actin?

  G (globular) actin and F (filamentous) actin
• How do actin filaments contribute to cell movement?

  They control cell shape and movement
• What type of structure do actin filaments form when bundled together?

  Very strong structures
• What are intermediate filaments made of?

  Rope-like fibers of α-helical monomers
• What is the function of intermediate filaments?

  Provide mechanical strength to cells
• How does the cytoskeleton change over time?

  It undergoes assembly and disassembly
• What influences cell-to-cell communication?

  Stable structures formed by cytoskeletal elements
• What contributes to the strength of multicellular structures?

  Internal cytoskeleton and cell-cell adhesions
• What are desmosomes primarily responsible for?

  Giving epithelium mechanical strength
• What do cadherins connect in desmosomes?

  Intermediate filaments of adjacent cells
• Where are desmosomes abundant?

  In epithelia and high mechanical stress tissues
• What is the role of adherens junctions?

  Cell-cell anchoring junctions
• What do cadherins form?

  Homodimers in cell membranes
• What is the significance of Ca$^{2+}$ in cadherins?


  It binds between cadherin repeats
• How many cadherin members are in the human superfamily?

  180 members
• What is the advantage of multicellularity?

  Cells can cooperate and specialize
• How do cadherins interact in adjacent cells?

  They interact weakly but collectively strong
• What happens when Ca$^{2+}$ is lost in cadherins?


  It affects cadherin structure
• What was the first cell adhesion study about?

  Coalescence and regeneration in sponges
• What did Wilson's sponge study demonstrate?

  Sponge cells recognize each other
• What is homotypic recognition in sponge cells?

  Recognition of the same species cells
• What is the significance of selective recognition in cells?

  Important for tissue assembly and repair
• How do cadherin interactions link actin cytoskeletons?

  Via anchor/adapter proteins like catenins
• What do adherens junctions form in epithelial cells?

  A continuous contractile belt around cells
• What can adhesion belts cause in epithelial layers?

  Invaginations and tubulation
• How do changes in cadherin expression affect cells?

  Impact development, tissue formation, and migration
• What is the connection between cadherins and cancer?

  Abnormal expression is linked to metastasis
• What do adherens junctions influence in epithelial layers?

  Coordinated contraction of cells
• What connects the ECM to the cytoskeleton?

  Focal adhesions
• What are integrins?

  Trans-membrane proteins connecting ECM to cytoskeleton
• What is the role of integrins in the cytoskeleton?

  Allow cytoskeleton to grip ECM molecules
• What type of protein is an integrin?

  α/β heterodimer
• What does talin link to in the cell?

  Actin filaments
• How many different β chains do integrins have?

  8 different β chains
• What is the significance of integrins' combinatorial repertoire?

  Distinct ligand binding properties
• How do integrins bind to ECM molecules?

  With low affinity, like Velcro