Midterm Review Slides Flashcards
What are the 4 general types of cellular movement?
- reorganization of the cytoskeletal network – growth of the cytoskeleton in one region of the cell pushes the cell membrane outward (amoeboid movement)
- motor protons ‘walk’ along relatively fixed elements of the cytoskeleton (can be used for cargo transport throughout the cell)
- motor proteins attached to the cell membrane (fixed) pull on the skeleton, moving an element of the cytoskeleton
- motor proteins and cytoskeleton are arranged such that they slide over each other, pulling the cell into a different shape
What are microtubules?
long hollow tubes composed of repeating units of tubulin (which is a dimer of alpha-tubulin and beta-tubulin)
How do microtubules grow and shrink?
- grow by adding tubulin dimers on the (+) end
- shrink by shedding tubulin dimers on the (-) end
What is the main factor that influences the rate of growth and the rate of shrinkage in microtubules?
concentration of tubulin (Cc)
- microtubule grows if the concentration of tubulin is greater than Cc
- microtubule shrinks if the concentration of tubulin is less than Cc
- Cc is lower for the (+) end of the microtubule compared to the (-) end
Where is the microtubule-organizing centre (MTOC)?
near the nucleus
Where is each end of a microtubule relative to the microtubule-organizing centre (MTOC)?
- (-) end is located at the MTOC
- (+) end extends out toward the cell membrane
Which motor proteins are associated with microtubules?
- kinesin
- dynesin
In what direction along the microtubule does kinesin and dynein move in?
polarity of the microtubule sets the direction of movement
- kinesin moves towards the (+) end
- dynein moves towards the (-) end
What are microfilaments?
long strands of the globular protein beta-actin (G-actin)
- G-actin polymerizes to form F-actin
How does the growth of F-actin (microfilaments) compare to microtubules?
similar to microtubules
- spontaneous growth
- has polarity
How does actin growth occur?
- capping protein on (-) end of F-actin to prevent shrinking
- growth at (+) end of F-actin (addition of G-actin monomers)
How does actin treadmilling occur?
- growth at (+) end of F-actin
- shrinkage at (-) end of F-actin
- a given G-actin monomer will move from the (+) to (-) end of actin
What is actin polymerization important for?
- amoeboid movement
- cell movement
What motor protein is associated with microfilaments?
myosin (many different types)
How might microfilaments and myosin work together to generate cellular movement?
- microfilaments act as tracks along which myosin moves (important for intracellular transport)
- myosin can pull on filaments
What is the function of myosin V?
recall myosin V moves towards the (+) end of actin filaments – towards the plasma membrane
- intracellular transport (cargo)
In what direction does myosin move along microfilaments?
- most known types of myosin move towards the (+) end
- EXCEPTION: myosin VI moves towards the (-) end
What are the functions of myosin VI?
recall myosin VI moves towards the (-) end of actin filaments – towards the nucleus
- intracellular transport (cargo)
- endocytosis
Sliding Filament Model
What are the stages of the cross-bridge cycle?
- ATP binds to myosin, causing myosin to detach from actin
- releasing actin causes myosin to hydrolyze ATP into ADP and Pi (which remain bound by myosin)
- ATP hydrolysis causes myosin to extend and attach to actin (forms a cross-bridge)
- release of phosphate promotes the power stroke
- ADP is released
Sliding Filament Model
What is unitary displacement?
the distance that myosin steps during each cross-bridge cycle
- this keeps them on track, and avoids interference with other things
Sliding Filament Model
What is the unitary displacement for myosin monomers?
variable
Sliding Filament Model
What is the unitary displacement for myosin dimers?
dependent on the periodicity of the actin filament
- ie. myosin V ‘walks’ along a microfilament with ~36 nm steps – 36 nm is the period of the helical actin filament
Sliding Filament Model
What is the duty cycle?
proportion of time during each cross-bridge cycle the myosin is attached to actin
- time spent in cross-bridge divided by time for full cross-bridge cycle
Sliding Filament Model
What is the duty cycle for non-muscle myosin?
0.5
- each myosin has 2 heads
- duty cycle of 0.5 means that each myosin head is bound to actin for half of the cycle (one myosin is bound for half of the cycle, and the other myosin is bound for the other half of the cycle)
- at least one myosin head is bound at all times, which will help prevent myosin from falling off the track of the microfilament