C 6 pts at ph 7 what of the protein molecules would

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Unformatted text preview: CH for its function. A. (3 pts) What type of weak interaction is indicated as broken line in the figure right? Electrostatic interaction or ionic interaction (or salt bridge). H- bond gets partial credit since ionic interaction is stronger. B. (6 pts) pKa of this tyrosine is unusually low (6.9). Provide an explanation why it is lower than usual. Electrostatic interaction with lysine stabilizes the deprotonated (conjugate base), negatively charged, form of tyrosine, which lowers the pKa. C. (6 pts) At pH 7, what % of the protein molecules would be functional? pKa = 6.9. CH CH2 O NH3 CH2 CH2 Tyr– is the functional form. pH = pKa + log [Tyr−]/[TyrH] log [Tyr−]/[TyrH] = 7.0 – 6.9 = 0.1 CH2 CH2 [Tyr−]/[TyrH] = 100.1 = 1.25 CH % = [Tyr−]/([TyrH]+ [Tyr−]) = 1.25 / ( 1 + 1.25 ) = 0.55 55 %. 2. [12 pts] A) (4 pts) Draw the structure of a generic di- peptide at pH 7. Use R for side chains. Draw H and C atoms explicitly. Don’t forget about charge(s). Chirality is not graded. B) (2) Indicate double bonds with arrows (either of the two resonance forms is ok). C) (2) Indicate Cα atoms by labeling it “Cα”. D) (2) Indicate all peptide bonds with arrows. E) (2) For residue 1, indicate the bonds corresponding to the rotation angles φ, ψ. peptide bond ψ φ R R +H Cα C H 3N H N C H O Cα O- O double bond Name: _____________________________________________________ 3 3. [25 pts] Muscle cells, which consume ATP rapidly, use phosphocreatine as a free energy reservoir to regenerate ATP...
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