Microtubules Flashcards
What is the function of the cytoskeleton?
Provides structure to the cell and play a role in cell movement.
- high level of internal organization on cells & enables them to assume & maintain complex shapes
- Cell movement and cell division, in eukaryotes it actively moves membrane-bounded organelles within the cytosol, cell signaling and cell-cell adhesion
Define Modularity
A small number of cytoskeletal elements are deployed in different locations and arranged in different ways to meet the needs of a particular cellular structure
What are the major structures of the cytoskeleton?
Microfilaments, intermediate filaments, and microtubules
Microtubules
Polymer of the protein tubulin, with a diameter of about 25 nm, that is an integral part of the cytoskeleton and that contributes to the support, shape, and motility of eukaryotic cells; also found in eukaryotic cilia and flagella
What are microtubules made of
Tubulin
Microtubules are the _____ structural elements of the cytoskeleton
Largest
Cytoplasmic microtubules
Loosely organized, dynamic network that pervade the cytosol and are responsible for a variety of functions:
- maintaining axons
- formation of mitotic and meiotic spindles
- maintains and alters cell shape
- disposition and movement of vesicles
Axonemal microtubules
Present in highly ordered bundles in the axonemes (the central shaft of a cilium or flagellum) of eukaryotic cilia and flagella and specialized for cell movement
What are protofilaments?
Linear polymer of tubulin subunits
Microtubules (MTs) are polarized structures with a ___ end and a ___ end
plus and minus
What is Nucleation?
Act of providing a small aggregate of molecules from which a polymer can grow. In other words, it is the initiation process of assembling subunits
What is elongation?
Growth of microtubules by addition of tubulin heterodimers to either end
What is the kinetic assembly of microtubules in vitro?
Microtubule formation is initially slow, a period referred to as the lag phase. This period reflects the relatively slow process of mT nucleation. The elongation phase–the addition of tubulin dimers– is relatively fast compared with nucleation. Eventually, the mass of MTs increases to a point where the [ ] of free tubulin becomes limiting. This leads to the plateau phase, where MT assembly is balanced by disassembly.
What is critical concentration?
The tubulin heterodimer concentration at which MT assembly is exactly balanced with disassembly
Addition of tubulin occurs at which end?
Plus end
When does treadmilling occur?
Arises when a given tubulin molecule incorporated at the plus end is displaced progressively along the MT and eventually lost by depolymerization at the opposite end
What is the dynamic instability model?
Model for microtubule behavior that presumes two populations of MTs, one growing in length by continued polymerization at their plus ends and the other shrinking in length by depolymerization
Microtubules commonly originate from a structure in the cell called a microtubule-organizing center (MTOC). What is MTOC?
Structure that initiates assembly of microtubules, the primary example being the centrosome
What is a centrosome?
Small zone of granular material surrounding two centrioles located adjacent to the nucleus of animal cells; functions as a cell’s main microtubule-organizing center
What is the role of MTOCs?
Their ability to nucleate and anchor MTs
What are some microtubule-stabilizing/bundling proteins?
Microtubule-associated proteins (MAPs), tau, and MAP2
What is MAPs?
Bind at regular intervals along the walls of MTs, allowing interaction with other filaments and cellular structures
What is tau?
Causes MTs to form tight bundles in axons
What is MAP2?
Is present in dendrites and causes the formation of looser bundles of MTs
What are +- TIP (+- end tubulin interacting) proteins?
They stabilize MTs by capturing and protecting the growing plus ends. They also decrease the likelihood that MTs will undergo catastrophic subunit loss
What are some microtubule-destabilizing/serving proteins?
Some of these proteins include: Stathmin/Op 18, Catastophins and ketanin
What does Stathmin/Op 18 do?
It binds to tubulin heterodimers and prevents them from polymerizing
What does Catastrophins do?
Act at the ends of MTs and promote peeling of subunits from the ends
What does Katanin do?
Sever MTs
What is “The Mesh”?
A network of microtubule connectors that stabilizes individual kinetochore fibers of the mitotic spindle where the chromosome attaches. The mesh holds and stabilizes MTs and holds two MT together at a time.
