1 The pKa for this amino acids side chain is 125 At physiolo

1) The pKa for this amino acid\'s side chain is 12.5. At physiological pH (7.4), the strongest interaction for this side chain is therefore likely to be?

a) Charge-charge (ionic)

b) Charge-dipole

c) Charge-induced dipole

d) Van der Waals (dispersion)

2. The side chain of this amino acid has a pKa of 3.65, at physiological pH (7.4), what would the ionization (dissociation) status of the side chain be?

a) 100% ionized (dissociated)

b) 90% ionized

c) 99% ionized

d) 50% ionized

H2N-CH-C-OH CH2 CH2 CH2 O LIC C-ICI-ICI-IC-11-N -IC11-

Solution

1) at pH = 7.4 > pka 12.5   we have   charge amino group side chain i.e C=NH2+

Hence major interactions would be   charge-dipole

2) pH = 7.4 , we have pka= 3.65

we use Henderson eq

pH = pka + log [ conjugate base] / [ acid]

7.4 = 3.65 + log [ conjugate base] / [ acid]

[conjugate base] = 5623 [ acid]

Let [acid] = 1M ( initially)   , at equilibrium [ acid] =1-X , [ conjugate base] = X

given X = 5623 ( 1-X)

X = 5623 / 5624 = 0.9999

Thus X% = 0.9999 x 100 = 99.99 %

Hence answer is option A