B: Motors, Actin, Cell Mobility (22) Flashcards
Define: exocytosis
Exocytosis: secretory vesicles deliver contents outside the cell
Define: endocytosis
Endocytosis: vesicles bring contents into cell
Define: autophagy
Autophagy: lysosomes recycle “used” organelles
Define phagocytosis
Phagocytosis: capture and destruction of pathogens like bacteria
What are the roles of Microtubule - associated Non Motor Proteins
Control MT organization in cytosol (ex. Tau protein)
Stabilize MTs or stimulate assembly
How are the +/- end different on MTs
+ end is dynamic
- end is stable
Which was does kinesin and dynein move in MTs
Kinesin is + end directed
Dynein is - end directed
How do MT associated motor proteins move?
Use ATP to generate force
Can move material along MT tracks
What are the 4 steps of movement of MT associated motor proteins
- AMP binding to the leading head induces a conformational change that swings the trailing head 108 degrees toward the (+) end of the microtubule
- The new leading head quickly binds to a tubulin subunit and releases its ADP, moving the kinesin’s cargo forward
- In the trailing head, ATP is hydrolyzed to ADP
- ATP binds to the leading head to repeat the reaction cycle
What does the moments of MT associated motor proteins generate in MTs
Motar MAPs generate sliding force between MTs
Important during mitosis and chromosome segregation
How does Kinesin and Dynein help the survival of Zebrafish
Allows a survival mechanism that redistributes melanin-granules for camouflage
– In the dark, melanin granules are dispersed outward by kinesin, causing the embryo to be darkly coloured
– In the light, melanin granules are aggregated toward the center by dynein, causing the embryo to be lightly coloured
What is the MTOC
Microtubule-Organizing Center (MTOC)
What does the MTOC do
Central site of MT assembly
Where is the MTOC found
Only in eukaryotes
What are the 2 main types of MTOC
Basal bodies associated with cilia and flagella
The centrosome associated with spindle formation
What are MTs formed from
Hollow tube formed from tubulin dimers
What are MFs formed from
Double helix of actin monomers
What are IFs formed from
Strong fiber composed of intermediate filament protein subunit
Are IFs found in all cells?
Exclusive to multicellular animal cells
What is the role of IFs
Provide structural support and mechanical strength
Are IFs stable?
Stable in comparison to MTs and microtubules
Non polar
What are IFs formed from
Arrangement of fibrous a-helical proteins
Are IFs used for transport
No bc non polar
What are examples of IFs
karatins : epithelial cells
Neurofilaments: neuron-specific
Lamins: nucleus of cells
What are MFs made from
Polymer of actin protein
What are the functions of MFs
Maintenance of cell shape
Cell movement
Vesicle transport (specifically in plants)
Muscle contraction
Cytokinesis (contractile ring)
What are the types of MF
Exists as monomer (G-actin) or polymer (F-actin)
Whats the role of Actin in MFs
Actin is the central component of MFs
Actin is an enzyme that binds and slowly hydrolyzes ATP
A MF is a double helix of actin molecule
What is the structure of G-actin MFs
4 subdivisions
Divided by central cleft
2 approx equal lobes
What is the structure of F-actin MFs
2 strands of subunit
One unit has 28 subunits of G-actin
——– 14 in each strand
Exactly 72nm
Are MFs simular to MTs?
MFs are dynamic like MTs
– MF have similar properties to MTs
Like MTs, the + end quickly assementles/disassembles
– The - end assembles/disassembles slowly
What are the 2 main steps of F-actin MF assembly:
- Nucleation
- Polymerization
Explain
the Nucleation in MF assembly
Early nucleation steps of G-actin polymerization are slow
G-actin - dimers - trimers - short filaments
Monomers can be added at both ends (but always faster at + end)
Process always reversible - ATP hydrolysis stimulates the destabilization of the polymer
Explain F-actin assembly
F-actin microfilaments can be arranged in loose array network (meshwork) or tight bundles/cables/fibers
Organization of these structures regulated by actin-binding proteins
How does the ARP2/3 complex help actin nucleation
Complex helps in the creation of branch points for the polymerization of new actin fibers
Arp2/3 complex starts polymerization at branch points
How does directed cell mobility work in MFs
Coordinated activity of actin-binding proteins controls microfilament formation in a lamellipodium to allow directed cell movement
What are myosins
Myosins: a superfamily of motor proteins associated with microfilaments
– Most myosin molecules move toward the + end of microfilaments
What are the 2 main types of myosins
- Conventional myosins
- Unconventional myosins
Explain conventional myosins
Type II
Primary motors for muscle contraction
Explain unconventional myosins
Types I and III - XVIII
Generate force and contribute to motility in non-muscle cells
What are the Roles of Actin-Associated Motor Proteins
Actin-based protrusion of leading edge (lamellipodium) powered by actin growth
Myosin -based contraction pulls trailing edge forward
Explain Vesicle Transport by MF-based motors
Microtubule-based and microfilament-based motors can cooperate in intracellular transport
Kinesin transfer vesicle to myosin motor protien
