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Adaptation of Arctic Fish Essay

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Introduction
Arctic fish display a remarkable case of adaptation, living in in low temperatures around 0˚C with areas of ice that can be -1.9˚C (DeVries, 1971). The ability for Arctic fish to thrive in such a low temperature environment is made possible by a class of proteins called Antifreeze proteins. Antifreeze proteins (AFPs) and Antifreeze glycoproteins (AFGPs) are polypeptides that are biosynthesized in animals, plants and fungi that prevent ice crystal formation (Griffith & Ewart, 1995). The most widely accepted mechanism for the prevention of ice formation by AFPs and AFGPs is called the adsorption-inhibition mechanism, which describes that the protein binds to water molecules and separates water molecules at a certain distance.
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As information unfolds, the evidence for each AFP or AFGP can be overwhelming to say the least, as is why sections are used to clearly separate the varied ideas expressed.
The following figure will be useful for locating mentioned species throughout the paper, it documents the 4 AFPs and AFGP and what species they are found in. Figure 1. Adapted from Cheng et al., 1998.
AFPs: Type I
AFPs display a striking amount of diversity in shape, size and the fish they reside in. Type I proteins display a distinct linear α-helix protein shape, small molecular weight, and high Alanine concentration, where types II, III, IV and AFGPs have more complex structures and higher molecular weights (Yang et al., 1988; Hobbs et al., 2011). Type I AFPs are found in certain species of polar Flounders, Lipiards and Cunner (Fletcher et al., 2001). The AFPs found in each species raised questions of convergent evolution, and homoplasy is still a valid argument because of several weak congruities (Fletcher). However, the preferred explanation for Type I evolution stands for common ancestry. Primary structure and overall amino acid homology is seen between flounder and sculpin, suggesting evidence for a synapomorphic trait. This is evident from a similar beginning N-terminus amino acid sequence in both species – across the sculpin’s blood serum proteins and flounder skin AFPs: Met-Asp-Ala-Pro-Ala (Fletcher; Gong et al., 1996).
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