The isoelectric point of a polypeptide or protein is equal to the pH at which the overall charge is equal to zero (0). 1 i Find the pH range to within 1 pH unit over which the polypeptide below will have an overall charge of 0. (In class on Friday, I worked out the changes in charge that the N-terminal -NH3+ and the C-terminal -COOH groups undergo over a limited pH range. Follow through to apply the same approach to all of the ionizing or dissociating groups, including the N-terminal and C-terminal groups, to estimate their separate, individual contributions to the overall charge on the polypeptide as a function of pH. 6, identify the two residues that control the transition for the polypeptide to acquire an overall charge of 0.) Alanyl-cysteinyl-lysyl-glutamyl-asparaginyl-histidinyl-tyrosine Ala - Cys A C *H3N. CH3 H SH - Lys - Glu - Asn His - Tyr K E N H Y HO. H H ■NH3* | NH₂ HNT NH H Гон JOH Ka values 7.0 8.4 10.5 4.1 6.0 4.0 10.5 ΣZavg

The isoelectric point of a polypeptide or protein is equal to the pH at which the overall charge is equal to zero (0). 1 i Find the pH range to within 1 pH unit over which the polypeptide below will have an overall charge of 0. (In class on Friday, I worked out the changes in charge that the N-terminal -NH3+ and the C-terminal -COOH groups undergo over a limited pH range. Follow through to apply the same approach to all of the ionizing or dissociating groups, including the N-terminal and C-terminal groups, to estimate their separate, individual contributions to the overall charge on the polypeptide as a function of pH. 6, identify the two residues that control the transition for the polypeptide to acquire an overall charge of 0.) Alanyl-cysteinyl-lysyl-glutamyl-asparaginyl-histidinyl-tyrosine Ala - Cys A C H3N. CH3 H SH - Lys - Glu - Asn His - Tyr K E N H Y HO. H H ■NH3 | NH₂ HNT NH H Гон JOH Ka values 7.0 8.4 10.5 4.1 6.0 4.0 10.5 ΣZavg

Introduction to General, Organic and Biochemistry

11th Edition

ISBN:9781285869759

Author:Frederick A. Bettelheim, William H. Brown, Mary K. Campbell, Shawn O. Farrell, Omar Torres

Publisher:Frederick A. Bettelheim, William H. Brown, Mary K. Campbell, Shawn O. Farrell, Omar Torres

Chapter22: Proteins

Section: Chapter Questions

Problem 22.49P: 22-49 Based on your knowledge of the chemical properties of amino acid side chains, suggest a...

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22-49 Based on your knowledge of the chemical properties of amino acid side chains, suggest a substitution for leucine in the primary structure of a protein that would probably not change the character of the protein very much.
Now let us look at a real amino acid, alanine. Fill in the chart below for each ionizable group. You need only the relationship discussed in the pdf posted and the numbers posted below. The next 6 questions will ask for the numbers you calculated for each of the letters below. pH when Average charge of group Group Ka pKa [A]/[HA] = 1 when pH = pK alpha-COOH ~10-2 A C alpha-NH3* ~10-9 В
Consider an amino acid with the following pKa values: pKa1 = 2.71 and pKa2 = 9.31 At what pH value in aqueous solution would this amino acid (its predominant form) exist as an anion?
For the amino acid alanine, the major species in solution at pH 7 is the zwitterionic form, which has a negatively charged carboxylic acid group and a positively charged amino group. There is a less common neutral form in which neither group is charged. The carboxylic acid group of alanine has a p?apKa of 3.3. The amino group of alanine has a p?apKa of 8.8. Estimate the ratio of the concentration of the neutral amino acid species to the zwitterionic species at pH 7.
All amino acids have two ionizable functional groups: an α‑amino group (average p?a of 9.4) and an α‑carboxylic acid group (average p?a of 2.2). Aspartic acid has an ionizable side chain (R group) with a p?a of about 3.8. One of the possible ionization states of aspartic acid is shown in the image. The protonated form of the R group of aspartic acid is shown in the structure. The ratio of the protonated form to the charged (deprotonated) form depends on the p?a of the R group and the pH of the solution. Select all the pH values at which the charged form of the R group would predominate.
For the amino acid alanine, the major species in solution at pH 7 is the zwitterionic form, which has a negatively charged carboxylic acid group and a positively charged amino group. There is a less common neutral form in which neither group is charged. The carboxylic acid group of alanine has a p?a of 3 The amino group of alanine has a p?a of 8 Estimate the ratio of the concentration of the neutral amino acid species to the zwitterionic species at pH 7. __?__x10^?
Match the following amino acids with their chemical properties H -N-CIC- A -A ✓ B но с D VE ✓ F ✓ G / CH3 CH3 CH B H но -N-C-C- feed C но -N-C-C- H CH₂ D HO -N-CIC- 1 H CH₂ OH E но ||| -N-C-C- II H CH₂ I CH₂ CH₂ CH₂ T NH3 I. Acidic II. Nonpolar III. Polar uncharged IV, Basic + F O HO -N-C-C- H CH₂ NH₂ G но | || -N-C-C- I H CH₂ 1
The image below is a positive ionization mode Electrospray ionization-mass spectrum (ESI-MS) spectrum for a peptide, obtained using high resolution mass spectrometry. If ionization occurs through de-protonation (assuming that the mass of a proton is 1.0 Da), what is the neutral mass of the peptide, in Da? 627.271 627.604 100 - 627.938 628.271 628.604 628.938 627.0 628.0 629.0 mass/charge (m/z) 628.271 626.271 1878.813 O 1884.813 % Abundance
Which amino acid has the greatest amount of negative charge at pH = 6.20?
Order the following types of bonding from strongest (=1) to weakest (=5) in a typical biochemical system. lonic interactions. Hydrogen bonds. London dispersion interactions. Dipole interactions. Covalent bonds.
Consider a "tripeptide" with the following features (at pH = 10.8) • The N-terminal amino acid is leucine • The middle amino acid is aspartate • The C-terminal amino acid is lysine i. What is the 1-letter symbol for each of these amino acids il. Calculate the net charge of the predominant ionic state of this tripeptide at pH 10.8. Show work.
Draw the predominant form of this amino acid at pH = 12.