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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Textbook Question
Chapter 2, Problem 22P
Consider a protein in which a negatively charged glutamic acid side chain (pks = 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. (Hint Consider lessons from Coulomb's law, and the Henderson-Hasselbalch equation)
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Students have asked these similar questions
For the following pentapeptides: Ser-Glu-Gly-His-Ala and Gly-His-Ala-Glu-Ser
A. Compute their isoelectric pH (pI). Show full solution. Use standard pKa values.
B. Do these peptides with the same amino acid composition have different net charges at pH 7.0? Explain briefly.
C. Would you expect the titration curves of the two peptides to differ? Why or Why not?
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.
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…
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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