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60 Cards in this Set
- Front
- Back
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Actin filaments:
-size -composition |
7-8 nm
Made of actin |
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Microtubules:
-size -composition |
25 nm
Made of tubulin |
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Intermediate filaments
-size -composition |
10 nm
heterogenous components |
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Myosin filaments
-size -composition |
size varies
made of myosin |
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What are all of these filaments?
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Cytoskeletal filaments
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What is the structure of microtubules like?
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A tube
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What are microtubules made of?
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Alpha and beta tubulin which form heterodimers
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How are a/B tubulin dimers arranged?
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As protofilaments
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What is the building block of the microtubule?
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The heterodimer of a/B tubulin
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How many protofilaments in a microtubule wall?
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13
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How do microtubules form?
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By selfassembly - even in a test tube.
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What is required for microtubules to self-assemble?
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-Critical concentration of heterodimers
-GTP -physiological conc of salts |
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What is a unique feature of microtubules?
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Their INHERENT POLARITY
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How can the polarity of microtubules be seen?
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By the fact that they have different rates of assembly at each end.
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At which end of the microtubule is association fastest?
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Plus end - the on rate
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What happens at the minus end?
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Dissociation - the off rate
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What is the phenomenon of heterodimers passing from the plus end to the minus end called?
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Treadmilling
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What regulates the assembly / disassembly of microtubules?
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the local concentration of GTP
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How does GTP affect microtubule assembly?
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It is essential for assembly at the plus end - if it's not there dissassembly will occur.
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What happens when a heterodimer binds to a microtubule?
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GTP is hydrolyzed
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What happens when the rate of assembly exceeds the rate of GTP hydrolysis?
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A gtp cap is formed and stabilizes the microtubule
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What happens when the rate of heterodimer addition slows?
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The cap is lost and the microtubule depolymerizes rapidly.
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What does the rapid association and dissassociation of MT's illustrate?
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That they have DYNAMIC INSTABILITY - regulated locally by the GTP concentration.
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What makes MTs unstable?
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When GDP-bound heterodimers in the interior catch up to the GTP cap and cause hydrolysis
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Where in the cell cycle are microtubules very important?
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In mitosis - they make up the bipolar mitotic spindle.
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When do mitosis spindle microtubules form and disintegrate?
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Form - during metaphase
Deform - after cell division |
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What are some anticancer drugs that interfere with MTs work?
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By binding spindle microtubules and either preventing disassembly or disrupting them.
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List 4 anticancer drugs that target microtubules:
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-Vinblastin
-Colchicine -Taxol -Vincristine |
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Where are the dynamic properties of the mitotic spindle particularly evident?
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-Rapidly dividing tissues
-Embryos |
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What are Microtubule organizing centers?
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Sites where polymerization of microtubules is organized or initiated.
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MTOC
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microtubule organizing center
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What are the 2 principle MTOCs?
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Centrioles
Basal bodies |
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What are centrioles functional in?
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Organization of the mitotic spindle
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Where are centrioles found?
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In the centrosome
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Where are Basal bodies?
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At the cell surface where cilia extend
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How do MTOCs function?
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By establishing uniform polarity of microtubules relative to other organelles
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What end of MTs is associated with microtubules?
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The minus end
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What do the structures of centrioles and basal bodies consist of?
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Microtubule TRIPLETS
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How many triplets are in a centriole?
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9
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What is gamma tubulin?
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A molecule structurally related to alpha and beta tubulin but it does not form tube structures.
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What is gamma tubulin found as?
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Part of y tubulin ring complex
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What is the function of the gamma tubulin ring complex?
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Initiation of polymerization at MTOCs
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What exactly does the y tubulin ring complex do?
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Caps the minus end of microtubules to prevent their disassembly
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What microtubule based organelles are found on most cell surfaces?
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Cilia and flagella
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What are functions of cilia and flagella?
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-Motility
-Sensory |
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What is the cytoskeletal component of a cilia/flagella?
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Axoneme
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What does the axoneme consist of?
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9+2 pattern - pair of normal MTs in the center, 9 outer doublets
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What do axonemes arise from?
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Basal bodies
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What is the structure of a basal body like?
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9 triplets arranged in a circle - just like centrioles
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So what are the two MTOCs?
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Centrioles and Basal bodies
-9 triplets arranged in a circle |
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What is a major function of MTs in neurons?
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Motility
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What type of motility is accomplished with MTs?
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-Ciliary bending
-Mitosis -Organelle translocation |
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What are the motors that move stuff along MT tracks?
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Dynein and Kinesin
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How do Dynein/Kinesin function as motors?
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By using ATP
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What is the motor for ciliary bending?
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Dynein
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How does Dynein cause ciliary bending?
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By causing relative sliding between microtubules within the axoneme
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What type of motility is caused by cytoplasmic dynein or kinesin?
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Motility on single cytoplasmic MTs - i.e. axonal transport
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In what direction along MTs does
-Kinesin move? -Dynein move? |
Kinesin: towards the pos end
Dynein: towards the neg end |
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How many ATPases are on each motor?
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2
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What is the movement of stuff along dynein and kinesin similar to?
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Crossbridge cycling of myosin
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