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Shvoong Home>Books>Customers of Molecular Motors Review

Customers of Molecular Motors

Book Review   by:Rathna Kumaran     Original Authors: Berg; Jeremy M.; Tymoczko; John L.; and Stryer; Lubert.
ª
 
Customers of Molecular Motors

Molecular Motors are the agents
which create the movements in living organism, acts as biological molecular
machines.

Following are the biologically important molecular motors

Motor proteins, Myosin, Kinesin,
Dynein, FoF1 ATP synthase, RNA polymerase, Actin, Topoisomerases, The bacterial
flagellum.



Molecular-Motor Proteins:

a.
Members of the P-Loop
NTPase Superfamily

b. Following are the Eukaryotic cells containing three families
of molecular-motor proteins: myosin, kinesins, and dyneins. These proteins move
along tracks defined by the actin and microtubule cytoskeletons of eukaryotic
cells, contributing to cell and organism movement and to the intracellular
transport of proteins, vesicles, and organelles.

c.
These proteins are homologous, containing core structures of
the P-loop NTPase family and ability to change conformations in response to
nucleoside triphosphate binding and hydrolysis, which are the key to
molecular-motor function.

d.
Motor proteins consist of motor domains
attached to extended structures that serve to amplify the conformational
changes in the core domains and to link the core domains to one another or to
other structures.



Is Myosin Move Along Actin Filaments?



The motile structure of muscle
consists of a complex of myosin and actin, along with accessory proteins.

Actin:

A
highly abundant 42-kd protein polymerizes to form long filaments. >Each
actin monomer can bind either ATP or ADP. Muscle
contraction requires the rapid sliding of thin filaments, based on actin,
relative to thick filaments, composed of myosin.

Myosin:

A motor domain moves along actin filaments in
a cyclic manner.

Following are the binding process.

(1) Myosin complexes to ADP and Pi bind
actin

(2) Due this interaction, Pi is
released

(3) Leads to a conformational
change, to a large motion of a lever arm that extends from the motor domain,
moving the actin relative to myosin;

(4) Replaces ATP to ADP, resetting
the position of the lever arm and releasing actin

(5) Returning the motor domain to its
initial state by hydrolysis of ATP.

The length of the lever arm
determines the size of the step taken along actin in each cycle. The ability to
monitor single molecular-motor proteins has provided key tests for hypotheses
concerning motor function.



Can the Kinesin and Dynein Move Along Microtubules?

Rather than actin, Kinesin and
dynein move along with the microtubules.

Microtubules are polymeric structures composed
of α- and β-tubulin, two very similar guanine-nucleotide-binding proteins. Each
microtubule comprises 13 protofilaments with alternating α- and β-tubulin
subunits. Kinesins move along microtubules by a mechanism pretty comparable to
that used by myosin to move along actin, but with differences.

1. ATP binding to kinesin favors
motor-domain binding rather than dissociation.

2. The power stroke is triggered by
the binding of ATP rather than the release of Pi.

3. Kinesin motion is processive



Are the Rotary Motor Drives Bacterial Motion????

To drive, Rotating flagella are
used by the motile bacteria. If they move counterclockwise multiple flagella on
the surface of a bacterium get together to form a bundle that efficiently drive
the cell through solution. If they move in clockwise, the flagella fly apart
and the cell stumble.
Published: October 08, 2007   
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