What can produce loss of GTP cap and the pre-tubulin pool to be low so you don't have enough GTP- bound tubulin?
tubulin and GTP shortage
- microtubule will probably fall apart
- tubules maintained by loss and addition of dimers
- w/o GTP, they fall apart
Explain the dynamic instability of microtubules.
1) At the + end, there is a GTP-tubulin cap. It acts as a primer for addition
2) More GTP-tubulin is added to the cap, and the tubule grows. GTP-tubulin in the tubule is slowly converted to GDP-tubulin
3) IF free GTP tubulin is low, more GTP-tubulin in the tubule is hydrolyzed to GDP-tubulin
4) The GDP cap is unstable and the tubule depolymerizes
In terms of the GTP cap, what is not needed?
Explain the GTP cap.
GTP energy; it doesn't take GTP energy to get them to bind together
it promotes elongation; dimers with GTP at the end of the microtubule
Why can centrioles be two different sizes in a cross section?
When prep for microscope, making sections can cause one to chip off
Explain the proximal and distal ends of the centrioles and basal bodies.
Explain the microtubules in the centrioles and basal bodies.
distal end: end that centriole grows from; hollow center
Proximal: only at the end; cartwheel structure in middle of structure made out of protein
there are triplets: A is complete, B is not and neither is C
There have to be proteins holding the triplets
9+0 arrangement
Explain the radial spokes of the MTOCs.
made of alot of different proteins; at elast 17
- found in chlamydomonas
- attached to central sheath at one end and subfiber A at the other
Unlike centrioles, what don't flagella and cilia have?
have triplets; there are only two
What is located in the cilia and flagella? What covers it?
How many microtubules? Explain them.
axoneme
plasma membrane
doublets: there are two
- A is complete with all 13 subunits; B is incomplete
What is coming off of microtubule A? How many?
What are they made out of? What do they act as?
arms
two: outer (three branches to it) and inner arm (two branches)
arms made of dynein; when isolated, it can act as Mg-independent ATPase
- important in movement
What comes off the subfiber B and attaches to the adjacent subfiber A?
What projects to the center of the axoneme? Explain them.
interdoublet links called nexin that are found at regularly spaced intervals (spacing different from dynein arms)
radial spokes; swollen at the central end
Microtubules are __ from the base to the tip. Dynein exists at __.
Explain tectin.
continuous
regular intervals
present where the two subfibers meet to make sure they dont come apart; similar in structure to intermediate filament proteins
What is the organization of the axoneme?
9+2
arrangement of things in the center
Structure of cilium.
- typical pattern of the axoneme?
- the characteristic __ of the __ has__ attached by spokes to a central cylinder. The intermediate part connects the axoneme to the __.
9+2 pattern with the central microtubule doublet and teh ring of nine doubets linked by pairs of dynein side arms
cartwheel structure
basal body
triplets
basal body
What is the distal end always connected to?
- What will accessory parts have to do?
to a cilium or flagellum
have to make the new structures that are in the axoneme but not in the bsaal body
What occurs at the tip of the flagella or cilium (the other end)?
capping area with plugs that fit in and prevent them from going ; it stops growth
Which tubule extends firther into the tip of the cilium?
What is the sliding-microtubule theory? Why is the contraction theory
the A-tubuleextends further into the tip of the cilium than the b-tubule
- teory that predicts that the B-tubules will be missing on the outer side of the bend
- theory that predicts the opposite result of the sliding-microtubule theory
Steps in a provisional dynein crossbridging cycle Steps A and B
a) the cycle begins with a dynein arm linked to an adjacent microtubule at the ninety degree position, the rigor position
b) Binding an ATP molecule from the medium causes a conformational change in the binding site at the tip of the dynein arm, so that it no longer fits the adjacent microtubule
Steps in a provisional dynein crossbridging cycle Steps C and D
c) The arm releases and hydrolyzes its bound ATP, but the products of hydrolysis remain bound to the arm
d) hydrolysis causes a conformational change, shifting the arm to the 45 degree position and reeactivating the microtubule-binding site at its tip. In this state, the arm stores much of the energy released by ATP hydrolysis
Steps in a provisional dynein crossbridging cycle Steps E and F
e) Reattachment to the adjacent microtubule releases the products of ATP hydrolysis and triggers release of the arm from its 45 degree position
f) the arm swivels forcefully through an arc of 45 degrees, sliding the attached microtubule along by an equivalent distance. The arm is now ready to ind a second ATp and repeat the cycle
__ also move cell structures such as mito along microtubules instead of __. In this type of motility, the structure would be subbed for the bottom microtubule (in the figure). THe __ would be fixed to the structure, and the tip would do whay?
dynein crossbridges
sliding one microtubule over another
crossbridge base
move the structure along the microtubule by attaching, swiveling, and releasing from the microtubule surface
Explain dynein attachment in terms of subfibers.
dynein is attached to subfiber A and extends to the adjacen doublets B
When the dynein arm is at a ninety degree angle, what does it do?
Once it does this, what happens next?
What happens next?
What have the microtubules done in relation to each other?
it binds ATP
once bound, it loses shape, causing dynein to lose its binding part, rendering it unable to bind
hydrolysis of ATP causing dynein to now hold ADP and a phosphate and change to a 45 degree angle position, binding to a new binding site and triggering ADP + P to leave--> back to same position
moved relative to each other
What prevents the microtubules from sliding past each other?
If this happens on one side of the flagella, what happens?
The subunitis that don't participate are what?
radial spokes nad nexin links restrict how far they slide past each other
it causes bending
passive backsliding
__ and __ have been implicated in determining where sliding occurs.
Some sliding activity __. Other activity __.
__ are not involved in this at all.
radial pokes and central sheaths
bends
beats
microfilaments
Explain centrioles.
cylindrical at right angles to one another
pairs
perpendicular arrangement
Explain pericentriolar paterial
tubulin dimers
a different type of tubulin called gamma tubulin, which forms a ring where the dimers can attach
- area around has to contain regular dimers
also has paracentrin
The mitotic spindle is constructed from __, each composed of __, __, and __. The __ emanating from opposite spindle poles have a __, where microtubule-associated proteins may __ them.
no physical contact between centrioles nad microtubule of mitotic spindle
basal body= MTOC
- they connect
How chromosomes migrate towards the centrosomes (the spindle poles) during anaphase A
- They were once thought to what?
- In reality, what do they do?
A kinetochore may __ and then __.
be reeled in by the kinetochore microtubules as the microtubules shortened at their centrosome end
the microtubules lose subunits from the kinetochore end
actively disassemble bound microtubules and then repeatedly grasp the remaining parts of one or more shortening microtubules as if the fibers were lifelines
How chromosomes migrate towards the centrosomes (the spindle poles) during anaphase A
- It is also possible that an as yet unidentified __ is stretched between the __ and a __, in which case the microtubules might do what?
__ of the microtubules would then permit the elastic substance to __.
elastic substance
kinetochore
pole
restrain the elastic substance from pulling on a chromosome
