In the most famous example of Lamarck’s theory, giraffes must have stretched their necks to reach foliage above them, and so their necks were lengthened. The longer necks were inherited, and over the course of generations, this process was repeated, and their necks got longer and longer. 

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#XL - Q Biochemistry

A second NPF is a large protein complex called WAVE

and requires small GTP-binding protein Rac1.

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#XL - Q Biochemistry

WASp activation requires two signals (This type of two-signal input, called coincidence detection):

1. regulatory phospholipid PIP2

2. small GTP-binding protein Cdc42

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One NPF is called WASp, as it is defective in patients with Wiskott-Aldrich syndrome.

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The major NPF family is characterized by the presence of a region called WCA (WH2, connector, acidic)

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#XL - Q Biochemistry

To nucleate the assembly of branched actin filaments, Arp2/3 needs to be activated by a nucleation promoting factor (NPF)

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#XL - Q Biochemistry

Formins are activated by membrane-bound Rho-GTP, a Ras-related small GTPase