Microtubules #15 Flashcards
What are the building blocks of microtubules?
Heterdimers of alpha and beta TUBULIN PROTEINS
What is the avg diamter of microtubules
~25 nm (largest of 3 types of cytoskeletal fibers)
What Nucleotide Binds to Nucleotide binding site>
GTP
- How does GTP interact with
- Beta Tubulin?
- Alpha Tubulin?
- GTP bound to beta tubulin –> hydrolyzed to GDP + Pi
- GTP bound to alpha tubulin–> not exchanged
How are protofilaments arranged in a hollow microtubule?
13 protofilaments
linear polymerization alph-beta-alpha-beta
What conditions FAVOR Microtubule ASSEMBLY (5)?
- Sufficient concentration of subunits
- Warm Temperature (37 degrees)
- Low Calcium
- GTP
- MAPs; drugs like Taxol
What are two statesthat Tubulins exist?
Unassembled heterodimers in solution and assembled (polymerized) microtubules (functional form)
What % of total tubulin in cells is assembled?
50% of total tubulin is assembled, the rest is in dynamic equilbrium and exchange with polymerized microtubutles
Is GTP requried for microtubule assembly?
While GTP favors assembly, Energy from GTP hydrolysis is NOT required for assembly b/c assembly proceeds in the presence of nonhydrolyzable GTP analogs
Function of GTP?
changes conformation of beta tubulin protein, makign it more assembly-ready
- How does GTP hydrolysis occur (fast/slow)?
- What does the hydorlysis do?
- Hydrolysis occurs with a slight delay after tubulin assembles into polymer
- known to reduce the binding affinity of the subunit for neighboring subunits and makes it more likely to dissociate
Are ends of GTP bound subunits more stable? or less stable?
More stable
How can you make purified populations of MTs?
By repeated frounds of assembly and disassebmly by cooling (disassembly) and warming (reformation of MTs)
After warming, centrifuge solution to pellet microtubules and repeat the process
When nucleating MT seed added to an in vitro assebmly reaction, what side (+ or -) preferentially grew
Positive side
