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26 Cards in this Set
- Front
- Back
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What are the roles of microtubules? |
1. Cell motility 2. Intracellular transport 3. Cell shape 4. Cell division 5. Cell polarity 6. Cell organisation |
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Describe the structure of a microtubule. |
Hollow tube made up of heterodimers of alpha and beta tubulin monomers. The head to fail binding of dimers forms promotofilaments - -of which there are 13 in each microtubule. |
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How does the B lattice in microtubules form?
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B lattice forms due to lateral contact between tubulin subunits of the same type. |
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Describe the polarity of microtubules. |
Intrinsically polar - both chemically and structurally. The positive end is the fast growing end and is where Beta tubulin is exposed. The negative end is the slow growing end and is where alpha tubulin is exposed. |
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Describe the in vitro growth curve of microtubules. |
Follows a sigmoidal curve. 1. Lag phase - nucleation 2. Log phase - elongation 3. Plateau phase - steady state |
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What is the critical concentration? |
The concentration of tubulin in the environment where polymerisation rate = depolymerisation rate |
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What conditions are required for continuous growth of microtubules in vitro? |
1. Free tubulin conc > critical concentration 2. Mg++ available 3. GTP avaliable 4. 37 degrees |
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What is the structure of coordination for microtubules? |
The central anchoring point - the centrosome / Microtubule organising centre |
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What are the roles of the centrosome? What key molecule is involved in each role? |
1. Nucleation - gamma - TURC 2. Anchoration - ninein |
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What are the constituents of the MTOC? |
A pair of centrioles and pericentriolar material |
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What do monomers of gamma tubulin form? What is the function of the polymer? |
Forms the gamma tubulin ring complex (gamme TURC) Plays a vital role in nucleation of the microtubule at the negative end |
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Describe the structure of a centriole. |
Barrel shape composed of nine triplet microtubules arranged in a pin wheel fashion positioned orthogonally. |
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What is the presumed role of the centriole? |
Not involved in nucleation of the MTs but rather evidence suggests a role in organising the pericentriolar material |
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What is the role of the MT anchor? |
Stabilises the negative end and prevents loss of subunits. |
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Tubulin monomers have an intrinsic ability to hydrolyse _____ (1) into _______ (2). This allows the phenomenon of _______ __________ (3) to occur. |
1. GTP 2. GDP 3. Dynamic instability |
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What is dynamic instability? |
Where the positive ends of a microtubule are unstable to the point where they are constantly growing and shrinking. |
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Describe the role of GTP in dynamic instability. |
GTP tightly bound to the Beta subunit of tubulin confers a stable - growing state. GDP bound to the Beta subunit of tubulin confers an unstable - shrinking state. |
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How does the shape of a protofilament change between growing and shrinking states? |
In the growing state the dimers are in a straight conformation meaning a straight protofilament. In the shrinking state the protofilaments are vurved. |
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What is the key feature of a growing filament which allows its straight conformation? Why does it form? |
The presence of a GTP cap as GTP is hydrolysed slower than tubulin monomers are added . |
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Why is dynamic instability vital? |
Allows rapid remodelling of microtubules - making them highly responsive to cellular signals & changes. |
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What is dynamic instability vital for? |
1. Spindle formation in cell division 2. Cell motility 3. Differentiation |
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What are the actin motor proteins called? |
Myosins |
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What are the microtubule motor proteins called? |
Kinesins and Dyneins
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Describe the domain formation of motor proteins. |
All motor proteins contain a globular head (motor) domain with ATP and microtubule or actin filament binding sites. |
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How are microtubules related to pigmentation? |
Microtubule motors typically allows placement of organelles around the cell e.g ER via kinesins. However pigment containing vesicles migrate out along MTs to darken cells or inward to lighten them such as in melanocytes. |
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Melanocytes alter their pigmentation in response to: |
Disperse pigment granules in response to an increase in cAMP - a 2nd messenger linked to external stimuli. |
