223.24

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Cell Biology 

223.24: Actin Filaments and Cell Movement

General Introduction

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 Actin Filaments (7nm)

!"# %& '()*+,(-.) /+ !0# 1'.2 3+2+3.*& 4&&.35,.

42) 642 2+/ .76'428. 1%/' !"# 92:, /'. 3+2+3.*

)%&&+6%4/.&

 Actin Filaments (7nm)

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Peripheral Membrane Proteins

spectrin 

 Actin Filaments (7nm)

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 Actin Filaments (7nm)

 Actin Filaments (7nm)

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 Actin Filaments (7nm)

 Actin Filaments (7nm)

lamellipodium

filopodium

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 Actin Filaments (7nm)

Leading edge

 Actin Filaments (7nm)

contraction

Transmembrane adhesion

receptors (integrins) anchor

cell to the extracellular

matrix while associating

with actin intracellularly

myosin motor proteins slide actin filament

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 Actin Filaments (7nm)

 Actin Filaments (7nm)

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 Actin Filaments (7nm)

 Actin Filaments and Muscle Contraction

Three basic muscle types

Smooth Cardiac

Skeletal, striated

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 Actin Filaments and Muscle Contraction

 Actin Filaments and Muscle Contraction

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Actin Associates with Myosin to Form Contractile Structures

Myosin I has a tail and globular ATPase head.

Myosin I is found in all cells and it is involved in

vesicular movement and cell shape changes

Myosin II form dimers that

have a tail and globular ATPase heads.

Myosin II is found in muscle cells and

is important in muscle contraction

 Actin Filaments and Muscle Contraction

Myosin II form thick filaments.

Myosin II is arranged as a dimer

with two globular heads and a coiled-

coil tail.

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 Actin Filaments and Muscle Contraction

Fig. 17-36 and 17-39

 Actin Filaments and Muscle Contraction

+ -

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 Actin Filaments and Muscle Contraction

Myosin head lacking boundATP attaches to actin filament.

ATP binds myosin head and myosin

releases actin.

ATP hydrolysis occurs but ADP and Pi

remain bound. The head is displaced by 5 nm

along the actin filament.

 Actin Filaments and Muscle Contraction

Myosin releases Pi

and powerstroke

occurs. ADP is released.

Myosin again is bound to

actin.

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 Actin Filaments and Muscle Contraction