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present where the two subfibers meet to make sure they don't come apart; symmetrical in structure
contain upper and lower caps that fit into the tip of a microtubule that anchor the axoneme to the plasma membrane and stop increase in length from occurring; stops growth
Explain microtubule movement in the shortest of words.
They simply bend. They do not contract.
What was one of the earliest theories proposed to explain axonemal bending?
that microtubules contract in the presence of ATP, causing the axoneme to bend toward the side of the cilium where the microtubules have contracted
What disproved the first theory of microtubule movement?
examining the cilium and noticing that the doublets on one side of a bending cilium were not shorter and thicker than those of the opposite side. Instead, the microtubules located on the inside of the ciliary bend were found to project further into the ciliary tip than the microtubules on the opposite side of the bend
Dynein will always be attached to __ and extend to __.
- subfiber A
- the adjacent B subfiber
What else does the PCM have?
How would you determine whether there were microtubules involved with kinetochores?
put alkaloids in the solution
From which end are the subunits lost from in chromosome micgraiton?
the kinetochore end
Two contrasting views of how the kinetochore generates a poleward force on its chromosome during anaphase
Which one is the suggested way?
- 1) microtubule motor proteins are part of the kinetochore and use the energy of ATP hydrolysis to pull the chromosome along its bound microtubules (depolymerization is not the driving force)
- 2) chromosome movement is driven by microtubule disassembly: as tubulin subunits dissociate, the kinetochore is obliged to slide poleward in order to maintain its binding to the walls of the microtubule (depolymerization is the driving force)
What is a third idea of chromosome movement during anaphase found in yeast?
- a ring (protein) wraps around microtubules connected to the kinetochore (DAM1)
- - depolymerization from protofilaments splitting apart, curling back and pulling the kinetochore (and thus the chromosome) along
In reality, what can happen in terms of movement?
momvements can vary with cells
What do overlapping polar microtubules have and why?
there are connections (sidearms like dynein) to allow sliding past each other
For elongation of the spindle by polar microtubules, what has to happen?
they have to polymerize in the center of the spindle
Where is most of the action in anaphase?
in the center of the spindle
advantage of anaphase b?
separates the two sets of chromosomes so there's less chance for error
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