D. Now for the hard part the biology. In actual cells, it is thought that the mi
ID: 143737 • Letter: D
Question
D. Now for the hard part the biology. In actual cells, it is thought that the micellar form of exon 3 is not present. Instead, it remains relatively extended and unstructured like exon 1 does because of the cytosolic interaction and the association with the chitin binding domain which is in the membrane. Instead, it has been shown that exon 3 takes a reversible B-turn conformation when physically stressed for instance, stressed by the pressure that results from the pre-jump posture of the limb. Upon release of the mechanical stress during the jump, exon 3 resumes its disordered state. This unfolded-folded-unfolded transition is referred to as an 'energy storage' capacity. If you think about it, in order for the bug to jump, the energy used to contract the muscles in the pre-jump posture must be released as work (flying or jumping) rather than lost as heat. Explain, in terms of entropy, how exon 3 of resilin appears to confer the ability of the tissue to have 'high energy storage capacity' during the movement of jumping or flying as well as how exon 1 of resilin allows it to be 'super-elastic."Explanation / Answer
Ans. Exon 3 encoded peptide contains 11 copies of a 13 residual sequence :GYSGHRPGGWDLG
and exon 1 encoded peptide contains 18 copies of a 15 residual repeating sequence:GGRPSDSYGAPGGGN.
Since both peptide sequence contains high presence of proline and glycine that provides the elasticity to the resilin.
However due to the absence of alpha helix it forms the randomly coiled structure and disordered structure which increases its entropy. This is because of the presence of high content of proline. Proline is bulky amino acid that cause the formation of kink in the peptide chain and it is not able to fit in the alpha helices.
Presence of tyrosine residues are able to form di and tri tyrosine cross links between proteins that also helps in their storing energy and providing elasticity which cause the entropy to entropy to increase or decrease during the movement of jumping and flying.
When stress is applied, there is an input of energy which causes exon 1 encoded peptide to respond quickly due to its high flexibility and then after that energy is passed onto exon 3 encoded peptide which transforms itself from the unstructured form to beta turn structure to store energy and causing entropy to change at different intervals.
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