Lecture 30 Cell Motility I

briefly, what does the gamma tubulin in the centrosome of micotubules do

nucleates them and protects the minus end

katanin

severs microtubule filaments

• sits on wall of GDP tubulin and use ATP to extract tubulin subunit

kinesis talk toward which end

plus end

dyne walk toward which end

minus end

what allows kinesin and dynein to walk in terms of their structure

the fact that they are dimers

what is the function of the head and tail of kinesin and dynein

head: binds and hydrolyze ATP to walk along microtubules

Tails: interact with cargo either directly or indirectly through adaptor proteins

• dynein usually needs adaptor

how do kinesin help position organelles in eukaryotic cells

through anterograde trafficking (to plus end)

• bind to ER as cargo and walk it out to plus end and stretch out ER network throughout cytoplasm

how do dynein help position organelles in eukaryotic cells

retrograde traffic to minus end

• keep Golgi around minus end around centrosome

when are myosin heads in their highest/rigor state compared to when kinesin is in their highest/most rigor state

myosin in rigor state when there is NO NUCLEOTIDE BOUND / ADP bound

kinesin in most rigor state when there is either no nucleotide or when they are ATP bound

describe how the kinesin walks

1. one head encounters microtubule, binding tightly, causing ADP to be released and ATP binds to empty nucleotide binding site = tight bound

2. neck linker throws second head forward

3. first head hydrolysis ATP, releasing ADP and Pi, leading head no exchanges its ADP for ATP

kinesin moves processively step by step

how does cytoplasmic dynein interact with cargo

through adaptor proteins

what allows for directional transport

microtubules pointing in the same direction

Summarize how fluorescent marker proteins and non-hydrolyzable ATP analogs can be used to study the activity of motor proteins such as kinesin or myosin.

we can see / track kinesin in space and time

• see that kinesin moves progressively toward plus end

• tail is usually tagged

Compare the functions and movements of cilia and flagella.

cilia moves fluid over cell surface due to dynein power stroke

flagella propels itself through liquid solution in wave form

both are extension of cell that are microtubule based inside

Describe the arrangement of microtubules inside a cilium or flagellum

the microtbule base structure inside cilia and flagella is called an axenin

• two microtubule doublets with dynein dimers in between so that they can walk along adjacent doublets

describe the arrangement of the axonem

9 + 2 arrangements

• doublets have one A and one B microtubule

  • dynein associate with A microtubule on tail

  • dynein head walk on B microtubule on adjacent doublet

  • center 2 are important for stability / organization

what happens if we phosphorylate our microtubule associated proteins (MAP)

they will not be recruited to microtubules because MAPS have a positive charge and microtubule tails have a neg charge

• allows us to repurpose our microtubules for things such as the mitotic spindle

result: MAPS not recruited to microtubules due to charge repel

name 2 functions of MT motors (K and D)

moving vesicles / directional transport

position organelle in eukaryotic cell

describe the dynein power stroke

• dynein is stable when ATP bound

• ATP hydrolysis releases microtubule binding domain and stalk swings forward, stretching the linker making it more reactive

• motor moves toward minus end of microtubule

**dynein produces microtubule sliding

in flagellum, dynein cause microtubule bending