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Questions and Answers
What is the isoelectric point (pI) of alanine?
What is the isoelectric point (pI) of alanine?
- 9.1
- 7.0
- 5.7 (correct)
- 3.4
Which term is used to describe substances that can act both as an acid or a base?
Which term is used to describe substances that can act both as an acid or a base?
- Polyprotic
- Amphoteric (correct)
- Cationic
- Zwitterionic
What group do amino acids have attached to the α-carbon at physiologic pH?
What group do amino acids have attached to the α-carbon at physiologic pH?
- – COO– and – NH3+ (correct)
- – NH2 and – NH3+
- – COOH and – NH2
- – OH and – SH
Which equation is useful for calculating the abundance of ionic forms of acidic and basic drugs?
Which equation is useful for calculating the abundance of ionic forms of acidic and basic drugs?
Why do uncharged drugs pass through membranes more readily?
Why do uncharged drugs pass through membranes more readily?
How does a weak acid, like aspirin, typically permeate through membranes?
How does a weak acid, like aspirin, typically permeate through membranes?
What is the isoelectric point of alanine?
What is the isoelectric point of alanine?
Which form of alanine predominates in solution when the pH equals pK1?
Which form of alanine predominates in solution when the pH equals pK1?
In the Henderson-Hasselbalch equation, what does pK1 represent for alanine?
In the Henderson-Hasselbalch equation, what does pK1 represent for alanine?
At what pH value will the amino group of alanine start dissociating significantly?
At what pH value will the amino group of alanine start dissociating significantly?
Which pair can serve as a buffer in the pH region around pK2 for alanine?
Which pair can serve as a buffer in the pH region around pK2 for alanine?
What happens when the pH is equal to pK2 for alanine?
What happens when the pH is equal to pK2 for alanine?
Which rule determines the one-letter symbol for an amino acid if only one amino acid begins with a particular letter?
Which rule determines the one-letter symbol for an amino acid if only one amino acid begins with a particular letter?
What is the one-letter symbol for glycine based on the rules of assigning symbols to amino acids?
What is the one-letter symbol for glycine based on the rules of assigning symbols to amino acids?
Which amino acid receives the one-letter symbol based on its similar sounding name?
Which amino acid receives the one-letter symbol based on its similar sounding name?
In which situation is the one-letter symbol for an amino acid assigned based on a letter close to the initial letter of the amino acid?
In which situation is the one-letter symbol for an amino acid assigned based on a letter close to the initial letter of the amino acid?
What determines the acidic and basic properties of amino acids in aqueous solution?
What determines the acidic and basic properties of amino acids in aqueous solution?
Which rule assigns B to Asx and Z to Glx as symbols for amino acids implying either aspartic acid or asparagine and either glutamic acid or glutamine?
Which rule assigns B to Asx and Z to Glx as symbols for amino acids implying either aspartic acid or asparagine and either glutamic acid or glutamine?
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Study Notes
Henderson-Hasselbalch Equation
- The Henderson-Hasselbalch equation can be used to analyze the dissociation of the carboxyl group of alanine, similar to acetic acid.
- The fully protonated form of alanine is denoted as I, and the isoelectric form is denoted as II.
Dissociation of Carboxyl and Amino Groups
- Alanine has two titratable groups: the carboxyl (– COOH) group and the amino (– NH3+) group.
- The carboxyl group has a higher dissociation constant (K1) and is more acidic than the amino group.
- The pKa for the carboxyl group is pK1, and the pKa for the amino group is pK2.
Buffer Pairs
- The – COOH/– COO– pair can serve as a buffer in the pH region around pK1.
- The – NH3 +/– NH2 pair can buffer in the region around pK2.
pH and pK
- When pH = pK1, equal amounts of Forms I and II of alanine exist in solution.
- When pH = pK2, equal amounts of Forms II and III are present in solution.
- At neutral pH, alanine exists predominantly as the dipolar Form II, with a net charge of zero.
Isoelectric Point
- The isoelectric point (pI) is the pH at which an amino acid is electrically neutral.
- For an amino acid with two dissociable hydrogens, the pI is the average of pK1 and pK2.
- The pI of alanine is 5.7.
Ampholytes
- Amino acids are amphoteric, meaning they can act as either an acid or a base.
- Amino acids with a negatively charged group (– COO–) and a positively charged group (– NH3+) are referred to as ampholytes.
Applications of Henderson-Hasselbalch Equation
- The equation is useful for calculating the abundance of ionic forms of acidic and basic drugs.
- Weak acids (HA) release a proton, forming a charged anion (A–), while weak bases (BH+) can release a H+.
- Uncharged forms of drugs can pass through membranes more readily.
Amino Acid Abbreviations and Symbols
- Each amino acid has a three-letter abbreviation and a one-letter symbol.
- One-letter codes are determined by unique first letter, common occurrence, similar sounding names, and letter proximity to the initial letter.
- Examples include I = isoleucine, G = glycine, F = phenylalanine, and W = tryptophan.
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