Histidine has pK(a1)=1.8, pK(a2)=09.2 an...

Histidine has `pK_(a1)=1.8, pK_(a2)=09.2` and `pK_(a3)=6.0`. The isoelectric point, PI of histidine is likely to be

in between 1.8 and 6.0

in between 6.0 and 9.2

below 1.8

above 9.2

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The correct Answer is:

Histidine is basic amino acid `p_(1)=(1)/(2)[p^(Ka_(2))+p^(Ka_(3))], p_(1)=(1)/(2)[9.2+6.0]=7.5`

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alpha - amino acids are high melting crystalline solids because of the zwitterion structure. They are moderately soluble in water. In acidic medium, alpha - amino acids exist as cations (I) and thus migrate towards cathode under the influence of an electric field. On the other hand, in alkaline medium, alpha - amino acids exist as anions (III) and thus migrate towards anode under the influence of an electric field. However, at some intermediate value of p^(H) , the concentration of the cationic form (I) and anionic form (III) will become equal and consequently the alpha - amino acid will exist primarily as the neutral dipolar ion (II). At this p^(H) , there would be no net migration of the amino acid in an electric field. This p^(H) at which there is no net migration of the amino acid under the influence of an applied electric field is called isoelectric point (pI). Each amino acid has a characteristic isoelectric point. The pH of an amino acid that does not have an ionisable side chain such as alanine isd average of pK_(a) values of the carboxyl group and the protonated amino group. H_(3)overset(+)(N)-overset("R")overset("|")("C")H-COOH overset(" "OH^(-)" ")underset(" "H^(+)" ")hArr H_(3)overset(+)(N)-underset("Zwitterion (II)")(overset("R")overset("|")("C")H)-COO^(-)overset(" "OH^(-)" ")underset(" "H^(+)" ")hArr underset((III))(overset(+)(N)-overset("R")overset("|")("C")H)-COO^(-) Further, the alpha - carbon of all the amino acids (except glycine) is chiral (asymmetric) and hence amino acids can exist in teo stereoisomeric forms i.e., D and L. However, all the nautrally occurring amino acids belong to the L - series. underset("L(-)Glyceraldehyde")(HO-overset("CHO ")overset("| ")underset(" "CH_(2)OH)underset("| ")("C ")-H)" " underset("L-Amino acid")(H_(2)N-overset("COOH")overset("| ")underset("R ")underset("| ")("C ")-H) In alanine, carboxyl group ionises at pK_(a1)=2.34 and ammonium ion at pK_(a2)=9.69 . The isoelectric point of the amino acid is at p^(H) .

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The pK_(al) and pK_(a_2) of an amino acid are 2.3 and 9.7 respectively. The isoelectric point of amino acid is

A buffer solution 0.04 M in Na_2HPO_4 and 0.02 M in Na_3 PO_4 is prepared. The electrolytic oxidation of 1.0 milli -mole of the organic compound RNHOH is carried out in 100 mL of the buffer. The reaction is RNHOH +H_2O to RNO_2 +4H ^(+) + 4e ^(-) The approximate pH of solution after the oxidation is complete is: [Given : for H_3O PO_4, pK_(a_1) =7.20 , pK_(a_2) =12]

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AAKASH SERIES-PROTEINS AND NUCLEIC ACIDS -LEVEL - II LECTURE SHEET (EXERCISE - I)

The pH value of a solution in which a polar amino acid doesn't migrate...
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The structural feature which distinguishes proline from alpha - amino ...
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Which amino acid is achiral ?
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Which is not a true statement ?
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Which of the following structure represents the peptide chain ?
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All common amino acids except one react with cold nitrous acid (HNO(2)...
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The amino acid cysteine often forms a disulphide bond with another nea...
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Peptides on hydrolysis gives
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Peptides are composed of amino acids joined by amide bonds. Which of t...
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Which of the following is used in a colour test of amino acid ?
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Isoelectric point is
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Histidine has pK(a1)=1.8, pK(a2)=09.2 and pK(a3)=6.0. The isoelectric ...
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Glutamic acid, H(2)N-CH(CH(2)CH(2)COOH)COOH has pK(a1),(alpha-COOH)=2....
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Which of the following is the major solute species in a solution of ly...
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In an electric field, if an amino acid migrates towards cathode, the p...
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During the process of digestion, the proteins present in food material...
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The helical structure or a secondary structure of proteins is stabilis...
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The destruction of the biological nature and activity of proteins by h...
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The primary structure of protein is based upon the
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