Biochemistry: Concepts and Connections (2nd Edition)
2nd Edition
ISBN: 9780134641621
Author: Dean R. Appling, Spencer J. Anthony-Cahill, Christopher K. Mathews
Publisher: PEARSON
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Chapter 2, Problem 14P
What is the molecular basis for the observation that the overall charge on a protein becomes increasingly positive as pH drops and more negative as pH increases?
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At pH 7.0, in what order would the following three peptides (described by their amino acid composition) be eluted from a column filled with a cationexchange polymer?Peptide A: Ala 10%, Glu 5%, Ser 5%, Leu 10%, Arg 10%, His 5%, Ile 10%, Phe 5%, Tyr 5%, Lys 10%, Gly 10%, Pro 5%, and Trp 10%.Peptide B: Ala 5%, Val 5%, Gly 10%, Asp 5%, Leu 5%, Arg 5%, Ile 5%, Phe 5%, Tyr 5%, Lys 5%, Trp 5%, Ser 5%, Thr 5%, Glu 5%, Asn 5%, Pro 10%, Met 5%, and Cys 5%.Peptide C: Ala 10%, Glu 10%, Gly 5%, Leu 5%, Asp 10%, Arg 5%, Met 5%, Cys 5%, Tyr 5%, Phe 5%, His 5%, Val 5%, Pro 5%, Thr 5%, Ser 5%, Asn 5%, and Gln 5%
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.
A peptide has the sequence: Glu–His–Trp–Ser–Gly–Leu–Arg–Pro–Gly1. What would be the net charge of the molecule at pH a) 3, b) 8, and c) 11? (Use pKa values. Do not calculate the value per se, but instead estimate considering only fully protonated, or deprotonated states. Then estimate the pI for this peptide.
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Chapter 2 Solutions
Biochemistry: Concepts and Connections (2nd Edition)
Ch. 2 - Suppose a chloride ion and a sodium ion are...Ch. 2 - Draw two different possible hydrogen-bonding...Ch. 2 - Prob. 3PCh. 2 - 4. What is the pH of each of the following...Ch. 2 - Prob. 5PCh. 2 - The weak acid HA is 2% ionized (dissociated) in a...Ch. 2 - 7. Calculate the pH values and draw the titration...Ch. 2 - What is the pH of the following buffer mixtures?...Ch. 2 - a. Suppose you wanted to make a buffer of exactly...Ch. 2 - Prob. 10P
Ch. 2 - You need to make a buffer whose pH is 7.0, and you...Ch. 2 - Describe the preparation of 2.00 L of 100 glycine...Ch. 2 - Carbon dioxide is dissolved in blood (pH 7.4) to...Ch. 2 - What is the molecular basis for the observation...Ch. 2 - The anno acid arginine ionizes according to the...Ch. 2 - It is possible to make a buffer that functions...Ch. 2 - A student is carrying out a biological preparation...Ch. 2 - Histidine is an amino acid with three titratable...Ch. 2 - Prob. 19PCh. 2 - A biochemical reaction takes place in a 1.00 ml...Ch. 2 - Is RNA-binding enzyme RNase A more likely to have...Ch. 2 - Consider a protein in which a negatively charged...Ch. 2 - Prob. 23PCh. 2 - Prob. 24P
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- At neutral pH, which of the following amino acids has a net positive charge, which has a net negative charge, and which is neutral? (Hint: Draw the various charged forms of each amino acid before deciding.)(a) Aspartic acid (b) Histidine (c) Valinearrow_forwardConsider a protein in which a negatively charged glutamic acid side chain (pKa=4.2)(pKa=4.2) makes a salt bridge (ion-ion interaction) with a positively charged histidine side chain (pKa=6.5)(pKa=6.5).arrow_forwardConsider a protein in which a negatively charged glutamic acid side chain(pKa = 4.2) makes a salt bridge (ion–ion interaction) with a positively charged histidine side chain (pKa = 6.5).(a) Do you predict that this salt bridge will become stronger, become weaker, or be unaffected as pH increases from pH = 7.0 to pH = 7.5?(b) Justify your answer with calculations of partial charges on these aminoacid side chains.arrow_forward
- Consider a protein in which a negatively charged glutamic acid side chain (pKa = 4.2) makes a salt bridge (ion–ion interaction) with a positively charged histidine side chain (pKa = 6.5). (a) Do you predict that this salt bridge will become stronger, become weaker, or be unaffected as pH increases from pH = 7.0 to pH = 7.5? (b) Justify your answer with calculations of partial charges on these amino acid side chains.arrow_forwardConsider the peptides Pro-Gin-Val-Phe-His-Asp-Cys and His-Gln-Pro-Cys-Asp-Phe-Val. How do these two peptides differ? (Select all that apply.) The two peptides have different compositions. The two peptides have different isoelectric points. The two peptides have different titration curves. The two peptides differ in amino acid sequence. [References] If you were to have a mythical amino acid based on glutamic acid, but one in which the hydrogen that is attached to the y-carbon were replaced by another amino group, what would be the predominant form of this amino acid at pH 12 if the pK, value were 10 for the unique amino group? (Select all that apply.) Both of the carboxyl groups are deprotonated. The amino acid-carries a negative 2 charge. The amino acid carries a negative 4 charge. The amino groups are in the form -NH". Both of the amino groups are deprotonated.arrow_forwardCurrently, aspartic acid is forming an ionic interaction with arginine in a protein. Part a) If arginine is replaced with glutamic acid, would the ionic interaction have its stability increased, decreased, or have no effect on the ionic interaction? Part b) If arginine is replaced with Lysine, would the ionic interaction have its stability increased, decreased, or have no effect on the ionic interaction? Part c) If arginine is replaced with isoleucine, would the ionic interaction have its stability increased, decreased, or have no effect on the ionic interaction?arrow_forward
- Consider a protein in which a negatively charged glutamic acid side chain (pKa = 4.2) makes a salt bridge (ion-ion interaction) with a positively charged histidine side chain (pKa = 6.5). Part A Do you predict that this salt bridge will become stronger, become weaker, or be unaffected as pH increases from pH = 7.2 to pH = 7.8? The salt bridge will become stronger. The salt bridge will become weaker. The salt bridge will be unaffected. Submit Part B Previous Answers Correct At pH = 7.2 the glutamic acid (Glu) side chain will carry a charge of ~ -1 (at 3 pH units above the pKa for Glu, the side chain will be almost fully ionized); whereas the histidine (His) side chain will carry a charge of < +0.5 (at pH = pK₂ the charge on His would be +0.5; since pH = 7.2 is above its pKa, it will carry less (+) charge as it becomes more deprotonated). As the pH increase to 7.8, the charge on Glu will remain ~ -1 and the charge on His will decrease; thus, this salt bridge is predicted to become weaker…arrow_forwardGiven the following Peptide: Q6 *H;N-Phe-Asp-Ala-Arg-Gy-His-Arg-Asp-Glu-His-Tyr-CO 6a. What is the peptide's net charge at pH 2.0, pH 6.0, pH 7.4, and pH 10.2? (show work) 6b. What is the approximate isoelectric point of this peptide?arrow_forwardConsider a short peptide with the sequence M-C-Q-L-Y-P-E-D-K. List the ionizable groups in this peptide, and the net charge of the whole peptide at pH a) 1.5, b) 7.0, and c)12.0.arrow_forward
- A mixture of Alanine (pl 6.02), Glutamic Acid (pl 3.22), Glycine (pl 5.79), Lysine (pl 9.74) and Threonine (pl 6.53) are separated by cation exchange chromatography. What is the order of elution of these amino acids if you use gradient buffer system from pH 10 to pH 2 ? v First 1. Alanine v Second 2. Glutamic Acid v Third 3. Glycine v Fourth 4. Lysine v Fifth 5. Threonine 6. No separationarrow_forwardDescribe the amino acid illustrated above (at pH = 7.0). (the following amino acid at pH = 7 (aqueous form): (COO-)–CH(NH3+)–CH2–(COO-)) it is a non-polar, positively-charged amino acid it is a polar, positively-charged amino acid it is a polar, uncharged amino acid it is a polar, negatively-charged amino acid it is a non-polar, negatively-charged amino acidarrow_forwardThe oligopeptide isolated from the brain of an animal has the sequence glu-his-tri-ser-tyr-gly-leu-arg-pro-gly. Determine the total charge of the molecule at pH 3.0; 5.5; 11.0. In what pH range is the isoelectric point of the peptide?arrow_forward
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