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How do organelles proliferate?
They grow in mass and split like cells but are appropriated to daughter cells after cell division.
3 purposes of the cytoskeleton
Order organelle, support membrane, help fix cell environment (communication).
Types of cytoskeletal proteins and diameter
- Actin, 7nm
- Intermediate filaments, 10 nm
- Tubulin, 25 nm
Where are intermediate filaments located and their role?
They surround the nucleus and extend out to peripheral organelle and membrane. The role is to resist stress (high conc. in cells w/ lots of mechanical stress).
Structure of intermediate filaments and organization
Heptad (repeat of specific 7 aa) with hydrophobic residue on position 1 and 4.
Exists as an dimer.
Dimers form tetramers that are antiparallel.
Tetramer pack together to make a rope/scaffold.
Made from tubulin. a-tubulin and b-tubulin form a dimer and act as the building block for microtubules.
13 protofilaments come together to form microtubule (hollow tubule).
How do microtubules assemble and disassemble
It depends on the GTP bound to b-tubulin (bot have GTP though). In the GTP form, it can bind. In the GDP form (after hydrolysis), it disassembles.
Grow on the (+) end.
(-) bound to centrosome (nucleation center for microtubules) and grow away from it.
GTP analogue that binds tubulin but cannot be hydrolyzed so microtubules can't break down easily
Binds free tubulin and prevents microtubule polymerization. Can't bind bound tubulin.
Binds tightly to microtubules and stabilizes it.
Involved in nucleation of microtubules.
Has 2 centrioles and a membrane. Membranes form ring structures that let tubulin chains grow out from it.
Lag phase of polymer growth may be due to ring structure forming.
Yeast has MAP ________. What does map stand for in the context of microtubules?
microtubule associated protein.
It is on the cap of growing chains and binds to Kar9 that helps with cell budding.