Topic 5: cytoskeleton, extracellular components, cell junctions

Question 1

Describe the cytoskeleton

Answer 1

• Network of filaments extending throughout cytoplasm
• 3 types
  1) Microfilaments = actin = thinnest
  2) Intermediate filaments = middle range diameter + different proteins = keratin
  3) Microtubules = tubulin = thickest

Question 2

What is the function of cytoskeleton?

Answer 2

• Mechanical support
• Maintains cell shape
• Anchors organelles
• Dynamic = assembled/disassembled to change shape of cell
• Cell mobility

Question 3

Describe microtubules

Answer 3

• Hollow rods
• Thickest component
• Helical polymer made by tubulin monomers
• α and β-tubulin dimers that make up 13 protofilaments
• Each dimer has 2 GTP bound
• +ve end = fast polymerization
• -ve end = slow polymerization
  FUNCTION:
• Mitotic spindle formation = separation of chromosomes
• Shape the cell
• Guide movement of organelles

Question 4

Explain microtubule stability

Answer 4

• Continuous polymerization/depolymerization controlled by = GTP hydrolysis
• GTP attached to β-tubulin = hydrolyze to GDP during polymerization
• GTP attached to α-tubulin = doesn’t hydrolyze

Question 5

What is the effect of some drugs on microtubule stability?

Answer 5

• Anti-mitotic drugs = inhibit spindle formation = anti-inflammatory + anti-cancer
• Colchicine = binds to tubulin monomers + inhibits polymerization = anti-inflammatory
• Taxol = binds to tubulin monomers + inhibits depolymerization during mitotic anaphase = anti-cancer

Question 6

Describe microtubule polymerization

Answer 6

• Orientation = -ve end towards centres +ve end towards cell periphery
• Begins at MTOC :
• Centrosome = non-dividing cells
• Basal body = flagellated + ciliated cells
• Polar body = some fungi
• Chromosomal kinetochores of the mitotic spindle = dividing cells during metaphase

Question 7

Describe centrosomes

Answer 7

• MTOC
• Consists of centriole pairs = each consist of 9 triplet microtubles
• Located near nucleus
• Pericentriolar material = space around centrosomes
  FUNCTION:
• Microtubule nucleation = initiation of polymerisation
• Contains γ-tubulin = facilitates nucleation of α/β tubulin dimers by binding to the -ve end of microtubules = induces polymerisation by forming rings into which microtubules assemble + elongate

Question 8

Describe microtubule’s role in motility

Answer 8

• Used as monorails for movement of cellular cargo
• From cell centre > periphery + vice-versa
• Microtubules interact with motor proteins = motility = transport cellular cargo towards opposite ends
• Vesicles can travel along network of fibers provided by cytoskeleton

Question 9

What are the 2 cytoplasmic motor proteins?

Answer 9

1) Dynein = transport from periphery to cell center = +ve > -ve end
2) Kinesin = transport from cell center to periphery = -ve > +ve end