ionization states of amino acids Flashcards
what is pH
expresses the availability of H+ in solution
- at pH 7 [H+] = 10^-7 M
at pH 7 carboxylic acid exists as…
COO- (carboxylate ion)
amino acids whose side chains might become charges at given pH
Asp, Glu, Tyr, Cys, Arg, Lys, His
+1 when side chain is protonated
Asp, Glu, Tyr, Cys
-1 when side chain is deprotonated
Arg, Lys, His
pKa
tells you where in the pH scale a group undergoes protonation
true or false - each ionizable group on a molecule has its own pKa?
true
true or false - an amino acid will have the same pKa when it is part of a peptide chain
false - it will be slightly different
what determines the ionization state of each group in a molecule
its pKa value and the pH of the solution
how to asses ionization states of a functional group
pH 1 unit higher or more than pKa: group is fully deprotonated
pH = pKa: 50% deprotonated 50% protonated
pH 1 unit less or more than pKa: group is fully protonated
true or false - the pH and pKa relationship tell you if a molecule is positive or negative
False, it tells you if it is protonated or deprotonated
true or false - there is no group that goes prom positive to negative when deprotonated
true
true or false - the pKa of s functional group is constant
true
amino acid backbone in the peptide bonded state
when amino acids are part of a protein they are uncharged because the amino and carboxylate groups are linked and not free to protonate or deporotonate
true or false - the charge of an amino acid only changes when its side chain becomes protonated or deprotonated
false, depending on the pH the carboxyl and amino group may become protonated/deprotonated contributing to the net charge
