3: Cytoskeleton and extracellular matrix

Question 1

Actin System

Answer 1

• actin based non-contractile structures beneath plasma membrane
• polymerization/depolymerization of cortical actin -> pseudopodia & phagocytosis
• monomer binders regulate actin nucleotide exchange (beta-thymosin, ADF/Cofilin, Profilin)
• > capping proteins, severing proteins, cross-linking proteins

Question 2

Function of cellular microtubules

Answer 2

1. distribution of organelles in cell during interphase & cytokinesis
2. support of cell shape, especially long protrusions (stiffness)
3. movement of organelles, vesicles and macromolecules

• > plus-end dynamic of microtubules in cells
• > minus-end organisation of MTs

Question 3

Motor proteins

Answer 3

• ATPases
• three main classes:
  1. myosin (actin cooperation - direction: to barbed end)
  2. kinesins (microtubules cooperation - direction: to plus end)
  3. dyneins (microtubules cooperation - direction: to minus end)

Question 4

Cells in connective tissues

Answer 4

1. Collagen
2. Elastic fibers (fibrillin & elastin)
3. Proteoglycans & Glycosaminoglycans

Question 5

Types of cellular junctions

Answer 5

1. Occluding junctions (tight & septate)
2. Adhesive junctions (desmosome, adhesion, hemidesmosome, focal contacts)
3. Communicating junctions (gap)