Podcast
Questions and Answers
What is the primary use of the Henderson-Hasselbalch equation?
What is the primary use of the Henderson-Hasselbalch equation?
Which form of alanine predominates at neutral pH?
Which form of alanine predominates at neutral pH?
At what pH does equal amounts of Forms II and III of alanine exist in solution?
At what pH does equal amounts of Forms II and III of alanine exist in solution?
Which group in alanine is considered a weaker acid compared to the carboxyl group?
Which group in alanine is considered a weaker acid compared to the carboxyl group?
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What does each titratable group of alanine have a pKa numerically equal to?
What does each titratable group of alanine have a pKa numerically equal to?
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Which form of alanine exists when the pH equals pK1?
Which form of alanine exists when the pH equals pK1?
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Which pair of groups can serve as a buffer around pK1?
Which pair of groups can serve as a buffer around pK1?
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What is the isoelectric point for alanine?
What is the isoelectric point for alanine?
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How does the dissociation constant of the -NH3+ group compare to that of the -COOH group in alanine?
How does the dissociation constant of the -NH3+ group compare to that of the -COOH group in alanine?
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$K2$ in the text refers to the dissociation constant for which group in alanine?
$K2$ in the text refers to the dissociation constant for which group in alanine?
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Study Notes
Isoelectric Point (pI)
- The isoelectric point is the pH at which an amino acid is electrically neutral, with equal positive and negative charges.
- For amino acids like alanine, pI is calculated as the average of pK1 and pK2, e.g., pI = (2.3 + 9.1) / 2 = 5.7.
- At physiological pH, amino acids possess both a negatively charged carboxyl group (–COO–) and a positively charged amino group (–NH3+).
- Amino acids such as glutamate, aspartate, histidine, arginine, and lysine have additional ionizable groups in their side chains.
Amphoteric Nature of Amino Acids
- Amino acids are amphoteric, meaning they can act as either an acid or a base, and are classified as ampholytes.
- Ampholytes are substances that can participate in acid-base reactions.
Henderson-Hasselbalch Equation Applications
- The Henderson-Hasselbalch equation helps calculate the proportions of ionic forms of acidic and basic drugs.
- Weak acids (e.g., aspirin) release protons (H+), forming negatively charged anions (A–) that cannot easily permeate membranes.
- Weak bases often have a charged protonated form (BH+) which becomes uncharged (B) after losing a proton, facilitating membrane passage.
Buffer Solutions
- Buffers resist pH changes when small amounts of acid or base are added, crucial for maintaining physiological pH.
- Buffers are created by mixing a weak acid (HA) with its conjugate base (A–).
- Maximum buffering capacity occurs at a pH equal to the pKa value of the weak acid, remaining effective within ±1 pH unit of pKa.
Dissociation in Amino Acids
- Each acidic and basic amino acid has an ionizable side chain group that contributes to overall charge.
- The dissociation constant for the carboxyl group of an amino acid is denoted as K1, different from Ka, due to the presence of a second titratable group in the molecule.
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Description
Learn how to calculate the isoelectric point (pI) of an amino acid by averaging the pK values of its dissociable hydrogens. Understand the concept of pI as the pH where an amino acid is electrically neutral.
