Voortgezette Celbiologie Evelien Floor
Microtubule cytoskeleton
Microtubules
Microtubules are cytoskeleton elements that are present in every eukaryotic cell. They are very
dynamic and have different functions:
Drive chromosome separation during mitosis
o Adding of taxol to a cell will result in cell division arrest and most likely apoptosis,
this is used to treat cancer
Required for organelle transport and attachment, they serve as rails for motor-based
transport
o Transport via microtubules is the fastest, if this transport is affected it can result in
cell death
Microtubules are polymers of the protein tubulin. The tubulin
subunit is itself a heterodimer formed from two closely related
globular proteins called -tubulin and -tubulin which are tightly
bound together by noncovalent bonds. These two tubulin proteins
are found only in this heterodimer, and each or monomer has
a binding site for one molecule of GTP. The GTP that is bound to -
tubulin is physically trapped at the dimer interface and is never
hydrolyzed or exchanged; it can therefore be considered to be an
integral part of the tubulin heterodimer structure. The nucleotide
on the -tubulin, in contrast, may be in either the GTP or the GDP
form and is exchangeable within the soluble (unpolymerized)
tubulin dimer.
A microtubule is a hollow cylindrical structure built from 13 parallel
protofilaments, each composed of αβ-tubulin heterodimers stacked
head to tail and then folded into a tube. The microtubule has a
distinct structural polarity, with -tubulins exposed at the minus
end and -tubulins exposed at the plus end. The plus end grows
and shrinks fast and the minus end slow.
Microtubule dynamics are profoundly influenced by the
binding and hydrolysis of GTP. GTP hydrolysis occurs
only within the -tubulin subunit of the tubulin dimer.
It proceeds very slowly in free tubulin subunits but is
accelerated when they are incorporated into
microtubules. Following GTP hydrolysis, the free
phosphate group is released and the GDP remains
bound to -tubulin. GTP-tubulin tends to polymerize
and GDP-tubulin to depolymerize. When the tubulin-
dimers at the end of the microtubule are GTP bound
this is called the GTP cap. When the GTP cap is lost,
shrinkage will be the result. When GTP is hydrolyzed
the tubulin dimers change its conformation which is
causing shrinkage.
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Microtubule cytoskeleton
Microtubules
Microtubules are cytoskeleton elements that are present in every eukaryotic cell. They are very
dynamic and have different functions:
Drive chromosome separation during mitosis
o Adding of taxol to a cell will result in cell division arrest and most likely apoptosis,
this is used to treat cancer
Required for organelle transport and attachment, they serve as rails for motor-based
transport
o Transport via microtubules is the fastest, if this transport is affected it can result in
cell death
Microtubules are polymers of the protein tubulin. The tubulin
subunit is itself a heterodimer formed from two closely related
globular proteins called -tubulin and -tubulin which are tightly
bound together by noncovalent bonds. These two tubulin proteins
are found only in this heterodimer, and each or monomer has
a binding site for one molecule of GTP. The GTP that is bound to -
tubulin is physically trapped at the dimer interface and is never
hydrolyzed or exchanged; it can therefore be considered to be an
integral part of the tubulin heterodimer structure. The nucleotide
on the -tubulin, in contrast, may be in either the GTP or the GDP
form and is exchangeable within the soluble (unpolymerized)
tubulin dimer.
A microtubule is a hollow cylindrical structure built from 13 parallel
protofilaments, each composed of αβ-tubulin heterodimers stacked
head to tail and then folded into a tube. The microtubule has a
distinct structural polarity, with -tubulins exposed at the minus
end and -tubulins exposed at the plus end. The plus end grows
and shrinks fast and the minus end slow.
Microtubule dynamics are profoundly influenced by the
binding and hydrolysis of GTP. GTP hydrolysis occurs
only within the -tubulin subunit of the tubulin dimer.
It proceeds very slowly in free tubulin subunits but is
accelerated when they are incorporated into
microtubules. Following GTP hydrolysis, the free
phosphate group is released and the GDP remains
bound to -tubulin. GTP-tubulin tends to polymerize
and GDP-tubulin to depolymerize. When the tubulin-
dimers at the end of the microtubule are GTP bound
this is called the GTP cap. When the GTP cap is lost,
shrinkage will be the result. When GTP is hydrolyzed
the tubulin dimers change its conformation which is
causing shrinkage.
1
