Question

Tell me the likely charges on the following amino acids at the indicated pH. Aspartic acid...

Tell me the likely charges on the following amino acids at the indicated pH.

Aspartic acid (pK 4.7) at a pH of 9

Glutamic acid (pK 4.7) at a pH of 2

Lysine (pK of 10.2) at a pH of 7

Lysine (pK of 10.2) at a pH of 10.2

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Answer #1

If the pH is lower than the pKa, then the compound will be protonated. If the pH is higher than the pKa, then the compound will be deprotonated.

pH < pKa => molecule will be protonated

pH > pKa = >molecule will be deprotanated

pH = pKa => molecule will be half protinated ans half deprotonated

Aspartic acid

pKa = 4.7; and pH= 9

pH > pKa so deprotonated. As it has 2 COOH groups the charge will be negative (- 2)

Glutamic Acid

pKa = 4.7; and pH = 2

pH < pKa ==> so protonated. charge will be positive (+1)

Lysine

pKa = 10.2; pH=7

pH < pKa ==> so protonated. charge will be positive

Lysine

PKa =10.2 and pH = 10.2

pH = pKa => molecule will be half protinated ans half deprotonated

So this will have positive charge as it has more amino groups

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