ANAT 262 Lecture : 45 (1).doc

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plumcod665

21 Aug 2012

School

McGill University

Department

Anatomy & Cell Biology

Course

ANAT 262

Professor

John Presley

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Document Summary

Example of dynamic process is complete remodeling of a microtubule array during a mi- tosis (changes from a network radiating through out a cell to a compact bipolar mitotic spindle) Afs and mts are polar structures with a plus end and a minus end that polymer- ize at different rates Polymerization is accompanied by ntp hydrolysis which renders afs and mts unsta- ble (related but not interdependent on each other) This dynamic instability gives the ability to depolarize and polymerize rapidly which is a key feature of af and mt function. Ex: complete remodeling of mt network during mitosis. Mts are essential for a broad range of cell functions: Transport - molecular motors (kinesins and dyenin) Cell shape and polarity - axon in neurons. Positioning of membrane enclosed organelles (ex: golgi and er) These different isoforms of alpha and beta tubulins show differences mainly in a short sequence of the 10-18 c terminal amino acids.

Related Questions

Activity: Dynamic Instability of Microtubules

Part A

What causes catastrophe of the microtubule in vitro?

the lack of tubulin heterodimers

non-motor Microtubule Associated Proteins (MAPs)

GTP hydrolysis

mutation of the Î²-tubulin

Part B

What is the role of GTP in microtubule polymerization?

GTP binds the alpha and beta tubulin subunits together to form the tubulin monomer.

GTP hydrolysis provides the energy for the polymerization of the microtubule.

GTP is a second messenger that signals the need for polymerization/de-polymerization.

GTP stabilizes the tip of the microtubule, allowing more monomers to be added.

Part C

What would happen in the treadmilling experiment if a non-hydrolyzable analogue of GTP were used?

The monomers would be unable to add to the plus end, and the microtubules would shrink until they disappeared.

The microtubule would treadmill until the new tubulin, with non-hydrolyzable GTP, reached the minus end, and then it would only extend at the plus end.

The microtubule would add monomers at both the plus and minus ends, growing in both directions.

The non-hydrolyzable GTP would stabilize both ends, causing treadmilling to stop.

Part D

What is the difference between the plus and minus ends of the microtubule in in vitro experiments?

The beta subunit of the tubulin is exposed on the minus end.

Polymerization occurs at the plus end.

The plus end has a lower critical concentration for tubulin heterodimers.

Catastrophe occurs at the minus end.

Part E

How would the drug taxol affect the in vitro dynamic instability and treadmilling experiments?

Taxol would block catastrophe at the plus end in the dynamic instability experiment but not depolymerization at the minus end in the treadmilling experiment.

Taxol would block the addition of tubulin in both experiments, leading to a destruction of the microtubules.

Taxol would stabilize the microtubules in both experiments, leading to polymerization without catastrophe.

Taxol would block depolymerization at the minus end in the treadmilling experiment but not catastrophe at the plus end in the dynamic instability experiment.

The cytoskeleton of an animal cell changes markedly betweenG₁ and early M phase (prophase) of the cell cycle. Foreach of the following sentences, choose one of the options enclosedin square brackets that best describes the changes to thecytoskeleton and its components.

Before mitosis, the number of centrosomes must[increase/decrease]. At the beginning of[anaphase/prophase] in animal cells, thecentrosomes separate in a process driven partly by interactionsbetween the [plus/minus] ends of microtubulesarising from the two centrosomes. Centrosome separation initiatesthe assembly of the bipolar mitotic spindle and is associated witha sudden [increase/decrease] in the dynamicinstability of microtubules. In comparison with an interphasemicrotubule array, a mitotic aster contains a[smaller/larger] number of[longer/shorter]microtubules. Extracts fromM-phase cells exhibit[increased/decreased/unchanged]rates ofmicrotubule polymerization and increased frequencies of microtubule[shrinkage/growth]. The changes in microtubuledynamics are largely due to [enhanced/reduced]activity of microtubule-associated proteins and[increased/decreased] activity of catastrophins.The new balance between polymerization and depolymerization ofmicrotubules is necessary for the mitotic spindle to move the[replicated chromosomes/daughter chromosomes] tothe metaphase plate.

fuchsiabee895

To divide, cells undergo a process called mitosis (discussed in Ch. 18) in which polymers of a protein called tubulin assemble to form microtubules, which are rope-like structures that help separate a cell into two cells during division. The graphic below depicts the polymerization of tubulin into a microtubule. If a cell in mitosis is cooled to 0Â°, the microtubules depolymerize into tubulin monomers. The same is true for microtubules made from pure tubulin in a test tube; they assemble readily at 37Â°C, but disassemble at low temperature. This behavior is governed by the basic thermodynamic equation: âG = âH â TÎS A. Decide what signs (positive or negative) of ÎH and ÎS must be to account for the temperature-dependent polymerization described above, and show how your choices account for polymerization of tubulin at high temperature and its depolymerization at low temperature. (Assume that the ÎH and ÎS values do not change with temperature).

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ANAT 262 Lecture : 45 (1).doc

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