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Lecture 15

Biochemistry- Lecture 15(with chapter).docx

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BCHM 2021
Julie Clark

Biochemistry Lecture 15 -Motor Proteins -myosin has a motor head on them -Myosin 2 -2 heavy chains and 2 light chains -tail= coiled- coil -found mostly in the muscle thick fibres - myosin heads in the opposite directions -Kinesin - move on the microtubules -2 heavy chains and 2 light chains -motor domain and coiled-coil tails -on microtubules and they walk to the plus end – most few go to the minus end -tail has the binding site  if it attaches to organelles  there is a binding site on the organelle or microtubules -carry organelles or slide microtubules Dynein -on mircotubules -all to the minus ened -variable number of chains -vesicle trafficking -cilia and flagella Question: There are no known motor proteins that move on intermediate filaments. Why? Answer: Intermediate filaments have no polarity, but actin filaments and microtubules do. Motor proteins wouldn’t have a sense of direction on intermediate filaments. Dynein Continued - motor protein mechanism -ATP binding and hydrolysis -large conformational changes -change in affinity for filament **Video 16.8-Myosin** Mechanochemical Cycle: 1) filament binding 2) large conformational change in motor protein 3) release from filament 4) relaxation of conformation 5) filament rebinding Myosin Cycle 1) no ATP, tight binding to actin 2) ATP binds, releases actin 3) conformational change - ATP hydrolysis -lever arm moves 4)binds to actin  Pi release power stroke 5) ADP leaves  tight binding to Actin Question: What causes rigor mortis in a dead body? Answer: ATP is rapidly hydrolysed when cells are deprived of oxygen. In the absence of ATP, myosin binds tightly to actin. **Video: 16.7- Kinesin** Kinesin Cycle -two heads work together 1) front head loses ADP and binds to the ATP tight binding to tubulin 2) conformational change  rear head forward -linker region  loose binding to tubulin 3) ATP hydrolysis and releases of rear head from the tubulin Examples of cytoskeleton and motor protein function **Video: 16-Cytoskeleton** - organelle transport  motor protein carry organelles -plus end directed kinesins -ER carried outward -minus –end directed dyneins  carry Golgi inward -myosin and acti
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