Introduction to the cytoskeleton 2 Flashcards
What are microtubules composed of?
Microtubules are composed of α- and β-tubulin dimers, which polymerize to form hollow cylindrical structures.
What cellular functions depend on microtubules?
Microtubules are essential for cell division (mitotic spindle), intracellular transport (cargo transport in axons), and motility (sperm flagella and cilia).
How do microtubules differ from actin filaments?
Microtubules are wider, longer, and stiffer than actin filaments, providing strong structural support and transport pathways.
Where do microtubules grow and shrink from?
Microtubules grow and shrink at their + end, showing dynamic instability. The - end is typically anchored at the microtubule organizing center (MTOC).
What triggers microtubule disassembly (catastrophe)?
Catastrophe occurs when GTP on β-tubulin is hydrolyzed to GDP, leading to destabilization and rapid disassembly.
What rescues a microtubule from disassembly?
Addition of fresh GTP-bound tubulin to the + end can rescue a shrinking microtubule.
What proteins stabilize microtubules?
Tau proteins and MAPs (microtubule-associated proteins) stabilize microtubules and prevent catastrophe.
What causes tau to lose its stabilizing effect?
Phosphorylation of tau (phosphotau) reduces its ability to stabilize microtubules.
What proteins sever microtubules?
Katanin (requires phosphotau) and spastin (acts independently) sever microtubules.
What is the MTOC and what does it do?
The MTOC, also known as the centrosome in dividing cells, anchors the - ends of microtubules and nucleates their growth.
What protein nucleates microtubules at the MTOC?
γ-tubulin, which forms a complex at the centriole, nucleates microtubules at their - ends.
What are motile cilia used for?
Motile cilia help move mucus in the respiratory tract and ova in the oviduct.
What is the role of primary cilia?
Primary cilia act as sensory organelles, detecting signals from the extracellular environment.
What role do microtubules and actin play in migrating cells?
Actin forms protrusions (filopodia, lamellipodia) for movement, while microtubules transport essential proteins and stabilize polarity.
Do cytoskeletal elements always serve the same function?
No, their roles vary by cell type and behavior, such as in migration or signal transport.
How do neurons extend their axons during development?
F-actin drives exploration and protrusion, while microtubules stabilize axon and dendrite growth.
How do leukocytes (like neutrophils) migrate?
Via amoeboid migration using actin-rich lamellipodia at the front and a contractile actin-myosin uropod at the rear.
Why is cell movement crucial?
It’s essential for tissue formation, immune responses, and wound healing.
What structures help cells grip and move along surfaces?
Focal adhesions connect the actin cytoskeleton to the substrate, allowing traction during migration.
How do cells detect and move toward chemical signals?
Filopodia detect chemoattractants, stabilizing lamellipodia, while the actin cytoskeleton and WASp help generate force for movement.
