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(A) At isoelectric point an amino acid h...

(A) At isoelectric point an amino acid has highest solubility.
(R) Isoelectric point ofan amino acid is usually at a pH value of

A

Both (A) and (R) are true and (R) is the correct explanation of (A)

B

Both (A) and (R) are true and (R) is not the correct explanation of (A)

C

(A) is true but (R) is false

D

Both (A) and (R) are false

Text Solution

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The correct Answer is:
D
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Isoelectric point is

At isoelectric point, amino acid is present as

Write notes on amino acids

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) .

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) Which of structural formula of lysine (NH_(2)-overset("COOH")overset("| ")("C ")H-CH_(2)-CH_(2)-CH_(2)-CH_(2)NH_(2)) at pH 13 ?

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) N - terminus of the peptide structure is on the

Which is not true of amino acid ?

Which amino acid is achiral ?

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

AAKASH SERIES-BIOMOLECULES-OBJECTIVE EXERCISE-4 (ASSERTION (A) & REASON (R) TYPE QUESTIONS :)
  1. (A) Denaturation of a protein can be done on heating or by adding a su...

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  2. (A) All enzymes are proteins but all proteins are not enzymes. (R) K...

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  3. (A) At isoelectric point an amino acid has highest solubility. (R) I...

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  4. (A) A protein chain tends to fold in a repeating geometric structure ...

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  5. (A) Entropy increases due to boiling of egg. (R) Breaking of tertiar...

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  6. (A) Amino acid that can be synthesised by human body is called essenti...

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  7. (A) At isoelectric point, the amino group does not migrate under the i...

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  8. (A) Albumin, present in egg white converting into water insoluble fibr...

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  9. (A) Rate of the hydrolysis of sucrose in the presence of acid is less ...

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  10. (A)alpha -amino acids have high melting point and show unusually high ...

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  11. (A) Proteins are step growth polymers of alpha- amino acids. (R) alph...

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  12. (A) The proteins are synthesised by various RNA molecules in the cell....

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  13. (A) Tertiary structure of proteins represents overall folding i.e. fur...

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  14. (A) Valine and Leucine are essential amino acids. (R) Both valine an...

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  15. (A) Leucine and isoleucine are structural isomers. (R) Isoleucine ha...

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  16. (A) Xerophthalmia is treated with vitamin - B6 (R) Xerophthalmia is...

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  17. (A) Insulin contains two peptide chains. (R) Insulin is an example o...

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  18. (A) Vitamin 'C' is ascorbic acid. (R) All acids are vitamins

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  19. (A) All hormone receptors are proteins, (R) All hormones are protein...

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  20. (A) Water soluble vitamins like ascorbic acid must be supplied regular...

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