B: Motors, Actin, Cell Mobility (22) Flashcards by Abbey Leswick

Define: exocytosis

Exocytosis: secretory vesicles deliver contents outside the cell

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Define: endocytosis

Endocytosis: vesicles bring contents into cell

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Define: autophagy

Autophagy: lysosomes recycle “used” organelles

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Define phagocytosis

Phagocytosis: capture and destruction of pathogens like bacteria

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What are the roles of Microtubule - associated Non Motor Proteins

Control MT organization in cytosol (ex. Tau protein)

Stabilize MTs or stimulate assembly

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How are the +/- end different on MTs

+ end is dynamic

end is stable

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Which was does kinesin and dynein move in MTs

Kinesin is + end directed

Dynein is - end directed

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How do MT associated motor proteins move?

Use ATP to generate force

Can move material along MT tracks

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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

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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

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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

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What is the MTOC

Microtubule-Organizing Center (MTOC)

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What does the MTOC do

Central site of MT assembly

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Where is the MTOC found

Only in eukaryotes

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What are the 2 main types of MTOC

Basal bodies associated with cilia and flagella

The centrosome associated with spindle formation

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What are MTs formed from

Hollow tube formed from tubulin dimers

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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:

1. Nucleation 2. 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

1. Conventional myosins 2. 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