Each ionizable group of an amino acid can exist in one of two states, charged or neutral. The electric charge on the functionalgroup is determined by the relationship between its pK and the pH of the solution. This relationship is described by theHenderson-Hasselbalch equation.Histidine has three ionizable functional groups. Complete the equilibrium equations by assigning the proper pK₁ for eachionization and the net charge on the histidine molecule in each ionization state.1-1-OHH₂N-C-C-OH1CH₂+HN-NHOH ||H₂N-C-C-0-|CH ₂HN-NHOOH ||H₂N-C-C-0-1CH₂-NH□HH₂N-C-C-0-LioCH ₂O-NH +2-2PK₁ = 1.8PK₁ = 7.59Answer BankpK₂ = 6.0+1-1PK₁ = 9.170

pKa is the pH at which half of the acid is dissociated. Given to us is the amino acid histidine with…

Answered: Each ionizable group of an amino acid…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Each ionizable group of an amino acid can exist in one of two states, charged or neutral. The electric charge on the functional group is determined by the relationship between its pKa and the pH of the solution. This relationship is described by the Henderson-Hasselbalch equation.(a) Histidine has three ionizable functional groups. Write the equilibrium equations for its three ionizations and assign the proper pKafor each ionization. Draw the structure of histidine in each ionization state. What is the net charge on the histidine molecule in each ionization state?(b) Draw the structures of the predominant ionization state of histidine at pH 1, 4, 8, and 12. Note that the ionization state can be approximated by treating each ionizable group independently.(c) What is the net charge of histidine at pH 1, 4, 8, and 12? For each pH, will histidine migrate toward the anode (+) or cathode (−) when placed in an electric field?
Each ionizable group of an amino acid can exist in one of two states, charged or neutral. The electric charge on the functional group is determined by the relationship between its pKa and the pH of the solution. This relationship is described by the Henderson-Hasselbalch equation. Lysine has three ionizable functional groups. The pKa for these groups are pK1 = 3.1, pK2 = 8.3 and pKR = 10.8. 1. Draw the structures of the predominant ionization state of Lysine at pH 1, 4, 8, and 12. Calculate also the net charge of each of these ionized molecules. Show your work. 2. Calculate the isoelectric point (pI) of Lysine in aqueous solution using the pKa values given above. Explain the rationale of your calculations and show your work.
Aspartic acid has a side chain bearing a carboxylic acid group; its pK, is ~4. The alpha-carboxylic and alpha-amino groups have pk, values similar to those of alanine, - 2 and ~9, respectively. Determine the net charge on an aspartic acid molecule at the following pH values (match each pH to the best choice). pH = 1 [ Choose ] pH = 2 [ Choose ] pH = 4 [ Choose ] pH = 7 [ Choose ] pH = 9 [ Choose ] pH = 13 [ Choose ] > > >
pI is the pH at which an amino acid exists as a zwitterion. A zwitterion has both a plus and minus charge so it is neutral overall. If the pH of a solution of tyrosine is much larger than the pI of tyrosine, which structure below represents the correct protonation state of tyrosine (tyrosine pI is 5.66; the pH of the tyrosine solution is 8.0)? NH NH H,N. HN. HO, OH но но но HO A В D
Aspartic acid has a side chain bearing a carboxylic acid group; its pkg is ~4. The alpha-carboxylic and alpha-amino groups have pk, values similar to those of alanine, ~ 2 and ~9, respectively. Determine the net charge on an aspartic acid molecule at the following pH values (match each pH to the best choice). pH = 1 +1 pH = 2 +1 pH = 4 pH = 7 -1 pH = 9 -2 pH = 13 -2 > > >
The following amino acid is dissolved in solution at pH 7.4. HC H' + CH CH₂ H/ H+ HC a. Which amino acid is this? (all lower case) N- H CH CH₂ b. What is the pKa of its ionizable side chain? (Use the value from the textbook.) c. What is the ratio of the uncharged to the charged form at pH 7.4? (write answer as number with one decimal place, ex 2.5 or 0.2 or 50.0 with an implicit "to 1")
To calculate the isoelectric point of amino acids having other ionizable functional groups, we must also take into account the pk, of the additional functional group in the side chain. For an acidic amino acid (one with an additional acidic OH group): For a basic amino acid (one with an aditional basic NH group): pK, (a-COOH) + pK, (second COOH) - pKa (a-NH3") + pK, (side chain NH) pl = a. Indicate which pK, values must be used to calculate the pl of each of the following amino acids: [1] glutamic acid; [2] lysine; [3] arginine. b. In general, how does the pl of an acidic amino acid compare to that of a neutral amino acid? c. In general, how does the pl of a basic amino acid compare to the pl of a neutral amino acid?
Amino acid Cys has ionizable groups with pKa values 2.0, 8.0, and 10.0. Determine the charge on the Cys at the following pH. Be sure to write the charge in fraction with sign in front (for example, +1/2, -1/5, and +7/8). Charge when pH is at 1.0? _________ Charge when pH is at 9.0? _________ Charge when pH is at 8.0? _________ Charge when pH is at 10.0? _________
A 100 ml solution of 0.1 M amino acid (AA) at ph 1.0 was titrated with NaOH solution. The pH was monitored, and the results were plotted on the graph. The keypoints in the titration are designated I to VII. What is the possible identity of the amino acid? What is the isoelectric point of AA? what is the pKa corresponding to the dissociation of the alpha carboxylic group? Region/point where AA is predominantly present as a (-1) charged species? The effective buffering range for the amino acid in the acidic region? Region/point where the solution has 50:50 percent mixture of the (0) and (-1) species
The peptide aspartyl-glutamyl-leucyl-threonyl-alanine, shown in the sketch drawing window, has several ionizable groups. Adjust the charges to show the molecule as it would exist at pH 5.00. Use the pk values in the table below. pK, Values for Ionizable Groups of Amino Acids. Amino Acid pA, of a-COOH pA, of e-NH, pA, of Side Chain Isoelectric Point (pI) Alanine 235 9.87 6.11 Arginine 2.01 9.04 12.48 10.76 Asparagine 2.02 8.80 5.41 Aspartic acid 210 9.82 3.86 298 Cysteine 2.05 10.25 8.00 5.02 Glutzmic acid 2.10 9.47 4.07 3.08 Glutamine 217 9.13 5.65 Glycine 235 9.78 6.06 Histidine 7.11 9.18 6.10 7.64 Isoleucine 232 9.76 6.04 Leucine 233 9.74 6.04 Lysine 218 8.95 10.53 9.74 Methionine 2 28 9.21 5.74 Phenylalanine 2 58 9.24 5.91 Proline 2.00 10.60 6.30 Serine 221 9.15 5.68 Threonine 2.09 9.10 5.60 Trуptophan 238 9.39 5.88 Tyrosine 2 20 9.11 10.07 5.63 Valine 2 29 9.72 6.00 • Use the wedge hash bond tools to indicate stereochemistry where it exists. • If a group is 2chiral, do not use…
What is the net average charge on the predominant form of lysine at pH values of (a) 2.0, (b) 5.0 and (c) 7.0? CLUE: draw the structure of lysine and show its different charged forms; then consider in which pH domains the pKa values for deprotonation/protonation occur.
The pK, of the α-carboxyl group of serine is 2.21, and the pK, of its α-amino group is 9.15. Calculate the average net charge on serine if it is in a solution that has a pH of 9.00. average net charge on serine:

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