Neo-Lamarckism - August Weismann

cut off the tails of mice for many generations and showed that this mutilation had no effect on the tail length of their descendants.

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#Unit 2. Cellular Organization

Vertebrate skeletal muscle contraction, also depends on set of specialized accessory proteins that are closely associated with the actin thin filaments:

a) Tropomyosin

b) Troponin

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#Unit 2. Cellular Organization

Tropomyosin (TM) is a ropelike molecule, about 40 nm in length, binds to 7 actin subunits in an actin filament.

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#Unit 2. Cellular Organization

Troponin, a complex of three polypeptides, 

TN-T (tropomyosin-binding)

TN-I  (inhibitory)

TN-C (Ca2+-binding)

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#Unit 2. Cellular Organization

TN-C is the calcium-binding subunit, controls the

position of TM on the surface of an actin filament through the TN-I and TN-T subunits

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#Unit 2. Cellular Organization

In the absence of Ca2+, muscle is relaxed

TM blocks myosin’s interaction with F-actin

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#Unit 2. Cellular Organization

Binding of Ca2+ ions to TN-C

triggers movement of TM to a new position on the filament, thereby exposing the myosin-binding sites on actin.