Question: serine and tyrosine have very different pkas for their sidechains...

Serine and tyrosine have very different pKas for their sidechains, even though both have a hydroxyl functional group in the sidechain.

1) What is the dominant ionization state of each amino acid sidechain under physiological conditions (in water at neutral pH, ~25 degrees Celsius)? Which amino acid sidechain will be deprotonated more easily under physiological conditions?

2) Use resonance structures to rationalize the difference between these pKa values.

3) Give an approximate numerical value for the difference in delta_G (the delta_delta_G) between the deprotonation of serine's sidechain vs. the deprotonation of tyrosine's sidechain.