The R group of lysine has a pK
a
of 10.5. What is the charge on the side chain at pH 7.4?

Question

The R group of lysine has a pK
a
 of 10.5.  What is the charge on the side chain at pH 7.4?

hcbiochem · Answer

It will be protonated and positively charged.

Remember that any ionizable group will be protonated if the pH < pKa, and it will be unprotonated if pH > pKa.

For the basic amino acids (His, Lys and Arg), their side chains when protonated are positively charged.
For the acidic amino acids (Glu and Asp), their side chains when protonated are uncharged, and when unporotnated, are negatively charged.

The R group of lysine has a pK a of 10.5. What is the charge on the side chain at pH 7.4?

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