Kinesin and Microtubules Molecular Motors

Microtubule Structure and Formation Polymer of two small dimers Polymer of two small dimers Alternating pattern of α- and β-tubulin Alternating pattern of α- and β-tubulin Alternation plays important role in Kinesin movement Alternation plays important role in Kinesin movement cyclopedia/M/microtubule.html ipedia/commons/8/80/Microtub le.jpg

Microtubule Structure and Formation Polymer structure allows for rapid assembly and disassembly Polymer structure allows for rapid assembly and disassembly Tubulin can diffuse rapidly throughout the cell Tubulin can diffuse rapidly throughout the cell Smaller tubulin can move more quickly than larger microtubules

Microtubules Unique bonding structure Unique bonding structure Resistant to thermal breakage along the strand Resistant to thermal breakage along the strand Dynamic ends that grow and recess rapidly Dynamic ends that grow and recess rapidly Leads to Dynamic Instability Leads to Dynamic Instability Tubulin will not organize (nucleate) on their own Tubulin will not organize (nucleate) on their own Require a pre-existing microtubule or a catalyzing protein Require a pre-existing microtubule or a catalyzing protein The cell takes advantage of this and can specify where the microtubules go

Microtubules This graph of an experiment on tubulin show the initial lag phase of three to five minutes where the tubulin are nucleating into the microtubule bases This graph of an experiment on tubulin show the initial lag phase of three to five minutes where the tubulin are nucleating into the microtubule bases

Dynamic Instability GTP- Tubulin Cap GTP-Tubulin GDP-Tubulin Hydrolysis

Dynamic Instability Hydrolysis goes faster than tubulin addition GTP-Tubulin GDP-Tubulin

Dynamic Instability GTP-Tubulin GDP-Tubulin New GTP Cap

Kinesin Kinesin has two ends Kinesin has two ends One end is the “tail end” which attaches to whatever is being transported such as a vesicle or organelle One end is the “tail end” which attaches to whatever is being transported such as a vesicle or organelle The other end has two “heads” which attaches to a microtubule. These two heads walk in a “hand over hand” fashion along the microtubule The other end has two “heads” which attaches to a microtubule. These two heads walk in a “hand over hand” fashion along the microtubule

“Hand-Over-Hand Movement” First head attaches, ADP is changed to ATP First head attaches, ADP is changed to ATP ATP causes the linking region to straighten, placing the second head in front ATP causes the linking region to straighten, placing the second head in front Second head attaches to microtubule Second head attaches to microtubule ATP in the first head is hydrolyzed into ADP and phosphate, head loses rigidity and detaches ATP in the first head is hydrolyzed into ADP and phosphate, head loses rigidity and detaches ATP is formed in the second head, moving the first head in front once again ATP is formed in the second head, moving the first head in front once again

procmotconvkinrev5.mov procmotconvkinrev5.mov procmotconvkinrev5.mov procmotconvkinrev5.mov Each step is 8 nanometers and the Kinesin travels.02-2 micrometers/second Each step is 8 nanometers and the Kinesin travels.02-2 micrometers/second

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