Lecture 19 Flashcards
what are the subunits of microtubules?
heterodimer (a/b) tubulin
what is alpha(a)-tubulin
the (-) end where GTP is NEVER hydrolyzed, just there
what is beta(b)-tubulin
the (+) end where GTP can be hydrolyzed/exchanges
what is a microtubule protofilament
one “string”/strand of heterodimer tubulins
what is the direction of assembly of microtubules?
at the (+) end
singlet
13 MT protofilaments in a ring formation
doublet
13+10 MT protofilaments in a 2-ring formation
triplet
13+10+10 MT protofilaments in a 3-ring formation
difference between microtubule and microfilament assembly occurrence
microfilaments can be assembled anywhere, microtubules can only be assembled from a small number of locations in the cell
where are microtubules assembled?
only at MTOC
what is MTOC
microtubule organizing centers, such as the centrosome
which cell type is does not strongly require MTOCs
dendritic cells
what end of the microtubules stays at the MTOCs?
the (-) end stays, (+) end radiates
what are centrosomes
made up of 2 centrioles at right angles of each other (mom and daughter centrioles)
what are centrioles composed of?
triplet MT protofilament rings
what triggers catastrophe?
when GTP hydrolysis rate is higher than assembly rate
what triggers rescue?
when GTP hydrolysis rate decreases and there is an increase of GTP-bound to b-tubulin
how are MT protofilaments assembled?
when there is a high concentration of GTP-b-tubulin added to (+) end
what is catastrophe
when microtubules have a GDP-b-tubulin cap = cause it to curve and limp and undergo rapid disassembly
what is rescue
when microtubules have a GTP-b-cap = favors assembly by adding more GTP-b-tubulins
what are the motor proteins of microtubules?
kinesin and dynein
what are kinesins?
microtubule motor proteins that move toward (+) end
what are the three parts of kinesins?
tail, stalk, and 2 heads
which part of the kinesin binds to the microtubule?
the heads
