Question

Cell Biology Tutorial - Microtubules (last one for now)

Answer 1

[This is a tutorial, not a question. Please save all comments or questions until the end. I will be handing out warnings and possibly suspensions for annoying or irrelevant spam comments.]

Answer 2

\({\bf{structure~and~organization}}\)

- made of α and β subunits. both can bind to GTP but only the β can hydrolyze it
- eukaryotes also have gamma subunit for microtubule assembly
- associated with MAPs (microtubule-associated proteins)
- tubulin assembly is preferentially at the (+) end
- 13 lateral protofilaments, each a string of alpha-beta dimers. there can also be doublets/triplets with 10 additional protofilaments for each added microtubule component

Answer 3

\({\bf{microtubule~organizing~centers}}\) assemble microtubules; anchored to the negative end so the positive end is free for assembly. ex. centrosomes in animals; basal bodies

gamma-TuRC: binds to alpha beta tubulin dimers for microtubule synthesis in centrioles

Answer 4

\({\bf{microtubule~dynamics}}\)

dynamic instability: switch between growth/decay of microtubule assembly (catastrophe/rescue)
growing protofilament - blunt end
shrinking protofilament - curved end
in absence of protofilament-protofilament interaction, the "rams horn" structure forms at the end of filament

MAP2 and tau protein stabilize microtubules, reducing catastrophe
+TIP associates with the plus ends of microtubules, promoting growth/suppressing catastrophe/attaching the plus end to other structures, etc.
kinesin-13 bind to tubulin and remove dimers

Answer 5

\({\bf{kinesins~and~dyneins}}\)

kinesins: towards (+) end, down axon (anterograde), powered by kinesin-1
dynein: towards (-) end, towards cell body (retrograde)

kinesin-1: N-terminal head domain + linker domain + tail domain, tails bind to the cargo, stalk domain dimerizes, linker domain is needed to move forward

Answer 6

\({\bf{basic~movement~mechanism}}\)

1. kinesin-1 motor head binds to ATP, conformational change that switches the leading/lagging head, where the lagging head "swings" forward
2. new leading head binds ahead of the old binding site
3. new leading head releases ADP and old leading head (the new lagging head) hydrolyzes ATP
4. linker becomes unlocked for new cycle

Answer 7

\({\bf{tubulin~modification}}\)

lystine acetylation: alpha only, needed for formation of stable cilia
detyrosylated: alpha only, removing carboxypeptidase from C-terminal tyrosine; resistant to kinesin-13 depolymerization
polyglutamylation/polyglycylation: addition of glutamic acid residues/glycine residues, respectively, to the glutamate residues. mutually exclusive. contributes to mictrotubule stability.

kinesin-1 associates preferentially w/ detyrosylated/acetylated microtubules, possib. for axon transport

Answer 8

\({\bf{This~is~the~end~of~my~tutorial;~I~hope~you~found~it~helpful.}}\)

\({\bf{If~you~have~any~*relevant*~comments~or~questions~I~will~attempt}}\)

\({\bf{to~address~them~to~the~best~of~my~ability.}}\)

\({\bf{Thank~you~for~reading!}}\)

Answer 9

The source of this information is \({\scriptstyle{Molecular~Cell~Biology~Eigth~Edition}}\)
\({\scriptstyle{Lodish,~et.al.}}\)

Answer 10

hey that may be useful for AP biology thank you!