Para-aminobenzoic acid has two ionizable groups. One is a carboxylic acid that ionizes through loss of a proton thereby forming a charged para-aminobenzoic acid carboxylate anion, and the other is an amine connected to an aromatic (benzene) ring that ionizes by accepting an H+ to form a positively charged ammonium ion. The pk of the carboxylic acid is 4.9 and the pk of the amino group is 2.5. Assume that the intracellular pH within a bacterial cell is 7.0. H H O-H pk = 2.5 Which of the following structures correctly depicts how most of the para-aminobenzoic acid is ionized at pH 7? A. B. H + H-N- H C. H H. + H-N- H N- H O-H pK₂ = 4.9 D. X o o O-H

Para-aminobenzoic acid has two ionizable groups. One is a carboxylic acid that ionizes through loss of a proton thereby forming a charged para-aminobenzoic acid carboxylate anion, and the other is an amine connected to an aromatic (benzene) ring that ionizes by accepting an H+ to form a positively charged ammonium ion. The pk of the carboxylic acid is 4.9 and the pk of the amino group is 2.5. Assume that the intracellular pH within a bacterial cell is 7.0. H H O-H pk = 2.5 Which of the following structures correctly depicts how most of the para-aminobenzoic acid is ionized at pH 7? A. B. H + H-N- H C. H H. + H-N- H N- H O-H pK₂ = 4.9 D. X o o O-H

Organic Chemistry

9th Edition

ISBN:9781305080485

Author:John E. McMurry

Publisher:John E. McMurry

Chapter26: Biomolecules: Amino Acids, Peptides, And Proteins

Section26.SE: Something Extra

Problem 50AP: The -helical parts of myoglobin and other proteins stop whenever a proline residue is encountered in...

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An amino acid mixture of phenylalanine, glycine and glutamic acid is to be separated bypaper chromatography. The solvent is less polar than water. Which of these amino acids will have the highest Rf value and which the lowest? Explain. Treatment of a new protein with dansyl chloride reveals two (2) dansyl-labelled derivatives of amino acids, alanine and methionine. What can you deduce about the structure of the protein from these results? Name the amino acids that contribute atoms to both purine and pyrimidine rings.
The isoelectric point (pl) of phenylalanine is pH 5.5. Draw the structure of the major form of glutamic acid at pH values of (a) 1 (b) 5.5 (c) 11.0.
A typical amino acid with one amino group and one carboxylic acid group, such as serine can exist in water in several iconic forms. Suggest the forms of the amino acid at low pH and at a high pH. Amino acids generally have two pKa values, one in the range of 2 to 3 and the other in the range of 9 to 10. Serene, for example, has pKa values of 2.91 and 9.21. Using species such as acetic acid and ammonia as models, suggest the origin of the two pKa values. Glutamic acid is an amino acid that has three pKa’s: 2.10, 4.07, and 9.47. Draw the structure of glutamic acid and assign each pKa to the appropriate part of the molecule. An unknown amino acid is titrated with strong base, producing the following titration curve. Which amino acid are likely candidates for the unknown?
(b) Describe how the charge of some amino groups in a protein might differ at pH 9.0 and pH 5.0. the charge on the amino group will differ at pH 5 and pH 9 which will depend on the pKa of the amino acid. (c) Describe how the charge of some carboxyl groups in a protein might differ at pH 9.0 and pH 5.0. charge on carboxyl group will differ at pH 5 and pH 9 which will depend on the pKa of the amino acid. (d) Given your answers to parts (b) and (c), what kind of intramolecular interactions in beta-galactosidase are most likely to be affected by a change in pH from 9.0 to 5.0? (e) Could the interactions you mention in part (d) affect the catalytic activity of beta-galactosidase?
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Explain the order of elution (with a buffer of pH 4) of the following pairs of amino acids through a column packed with Dowex 50a. aspartate before serine c. valine before leucineb. serine before alanine d. tyrosine before phenylalanine
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How does the shape of a titration curve confirm the fact that the pH region of greatest buffering power for an amino acid solution is around its pK's? Name four factors (bonds or other forces) that contribute to stabilizing the native structure of a protein, and describe one condition or reagent that interferes with each type of stabilizing force. Why is silk fibroin so strong, but at the same time so soft and flexible?
A typical amino acid with one amino group and one carboxylicacid group, such as serine, can exist in water in several ionic forms. (a) Suggest the forms of the amino acidat low pH and at high pH. (b) Amino acids generally havetwo pKa values, one in the range of 2 to 3 and the other inthe range of 9 to 10. Serine, for example, has pKa values of2.19 and 9.21. Using species such as acetic acid and ammoniaas models, suggest the origin of the two pKa values.(c) Glutamic acid is an amino acid that has threepKa's: 2.10, 4.07, and 9.47. Draw the structure of glutamicacid, and assign each pKa to the appropriate part of themolecule. (d) An unknown amino acid is titrated withstrong base, producing the following titration curve.Which amino acids are likely candidates for the unknown?
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