Helical groove

Helical grooved roller of hardened steel rotates counter clockwise... 

In smooth muscle, caldesmon plays an analogous role to that of troponin in striated muscle in that it blocks the myosin binding sites. The CaCM complex removes caldesmon from its binding on the thin actin filaments allowing tropomyosin to reposition in the helical grooves of F-actin leading to myosin ATP ase activation. 

Schlafi, D. and Zweifel, Y., Barrier Screws in Helically Grooved Barrels Operating Characteristics and Implications for Simulation Models, SPEANTEC Tech. Papers, 47, 195 (2001)... 

Figure 25-23 Schematic representation of configuration of DNA, showing the relationship between the axes of hydrogen-bonded purine and pyrimidine bases and the deoxyribosephosphate strands. There are 10 pairs of bases per complete 360° twist of the chain. The spacing between the strands is such that there is a wide and a narrow helical groove around the molecule. Proteins known as histones coordinate with DNA by winding around the helix, filling one of the other of the grooves. The histone-DNA combination is important in regulating the action of DNA.

Nature has found two basic ways of arranging the multiple capsid protein subunits and the viral genome into a nucleocapsid. In some viruses, multiple copies of a single coat protein form a helical structure that encloses and protects the viral RNA or DNA, which runs In a helical groove within the protein tube. Viruses with such a helical nucleocapsid, such as tobacco mosaic virus, have a rodlike shape. The other major structural type is based on the icosahedron, a solid, approximately spherical object built of 20 identical faces, each of which is an equilateral triangle. 

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