Table I. pK values of some amino acids amino acid pK of side chain or terminal g
ID: 142758 • Letter: T
Question
Table I. pK values of some amino acids amino acid pK of side chain or terminal group Alanine (Ala or A) Arginine (Arg or R) Asparagine (Asn or N) Aspartic acid (Asp or D) Cysteine (Cys or C) Glutamic acid (Glu or E) Glycine (Gly or G) Histidine (His or H) Leucine (Leu or L) Lysine (Lys or K) Phenylalanine (Phe or F) Serine (Ser or S) Tryptophan (Trp or W) Tyrosine (Tyr or Y) Valine (Val or V) peptide N terminus peptide C terminus uncharged 12.5 uncharged 3.9 8.3 4.3 uncharged 6.0 uncharged 10.8 uncharged uncharged uncharged 10.9 uncharged 7.8 3.6 What do you expect the charge of this protein will be at pH 2? Submit Answer Tries 0/3 What do you expect the charge of this protein will be at pH 9? Submit Answer Tries 0/3 What do you expect the charge of this protein will be at pH 14? Submit Answer Tries 0/3Explanation / Answer
From the Henderson-Hasselbalch equation the charge of the protein can be found. Recall the pH values which are acidic, basic and neutral. As the pH raises the positive ions are added i.e, H+ ions. When the pH increases, the nitrogen will lose its proton and thus its charge.
When pH is 2: we have many protons in the solution and it is protonated.As the solution is more acidic now more number of H+ ions are added making the solution more charged. There will be a positive charge of +1.
When the pH is 9, the solution is neutral to basic now. More number of OH- ions are added and there is deproteination. The net charge is zero because the solution contains equal number of H+ ions and OH- ions.
When the pH is 14, it implies it is completely basic than the pH 9 solution. More OH- ions are added making the solution more negatively charged.
Remeber: when the pH raises (by addition of basic solution) OH- ions are added increasing the negative charge. When the pH is low the negative charges remain and the charge remains positive.
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