Questions and Answers
What functional groups are present in amino acids?
What distinguishes L-amino acids from D-amino acids?
Which ion predominates at pH 7 for amino acids?
What is the role of the side chain group (R) in amino acids?
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Which of the following best describes a peptide bond?
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Which property allows amino acids to act as both acids and bases?
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What is the significance of the three-dimensional structure of amino acids?
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Which statement is correct regarding the stereochemistry of amino acids?
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What is formed when an amino acid is in its zwitterion form?
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Which amino acids are exclusively found in connective tissue proteins like collagen?
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At neutral pH, which form do free amino acids tend to exist in?
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What characterizes the titration curve of alanine?
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Which statement is true regarding amino acids without charged side chains?
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What happens to an amino acid's structure when it is titrated?
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What is true about the cationic form of an amino acid?
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What distinguishes histidine from standard amino acids during titration?
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What does the isoelectric pH (pI) represent for a molecule?
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How is the isoelectric pH (pI) calculated for glycine?
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What is the calculated pI for aspartic acid?
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At low pH, which amino acid is most likely to have a net charge of +2?
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What is the pI calculated for lysine?
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What is the pI for glutamic acid based on the provided values?
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Which of the following amino acids is likely to have a net charge of -2 at high pH?
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Which equation is used to calculate the pI for basic amino acids?
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Which amino acids are classified with basic side chains?
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What is the pKa of the side-chain imidazole group of histidine?
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What is the ratio of uncharged to charged side chains of histidine at pH 7.0?
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Which of the following amino acids has a nonpolar side chain?
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Which amino acid contains a guanidino group in its side chain?
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Why is serine not classified as having a basic or nonpolar side chain?
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Which amino acids share a structural parent with distinct derivatives?
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Which of the following statements about basic amino acids is accurate?
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Which amino acid is unique because it does not have a chiral center?
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What is the typical configuration of most alpha-amino acids at the alpha-carbon?
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Which of the following amino acids contains a sulfur atom in its side chain?
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Which characteristic is NOT associated with the amino acid proline?
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In amino acids with nonpolar side chains, which of the following amino acids is categorized as aromatic?
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Which of the following amino acids is NOT classified as nonpolar (hydrophobic)?
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Which amino acid is typically represented by the one-letter abbreviation 'W'?
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Which term is used to denote the first carbon in the side chain of amino acids?
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Study Notes
Amino Acids Overview
- Amino acids consist of an amino group (—NH2), a carboxyl group (—COOH), and a side chain (R) attached to the α-carbon.
- Most amino acids in proteins are L-amino acids, which are chiral and have a specific stereochemistry akin to L-glyceraldehyde.
- Glycine is the only amino acid without a chiral center.
Structural Properties of Amino Acids
- All amino acids except glycine exhibit chirality with at least one chiral center at the α-carbon.
- Amino acids are frequently categorized by side chains into nonpolar, polar, acidic, and basic groups.
- Common abbreviations for amino acids follow either three-letter or one-letter formats.
Classifications of Amino Acids
- Nonpolar amino acids (hydrophobic) include: glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, tryptophan, methionine.
- Basic amino acids with positively charged side chains at physiological pH (near 7) include: histidine, lysine, and arginine.
- Amino acids with nonpolar side chains include alanine, leucine, and phenylalanine; histidine and lysine are categorized as basic.
Titration and Zwitterions
- Amino acids act as both acids and bases, exhibiting zwitterionic forms at neutral pH—carboxyl groups carry a negative charge, while amino groups carry a positive charge.
- Neutral amino acids exist as zwitterions and have no net charge.
- The titration curve of an amino acid demonstrates how its functional groups react with hydrogen ions, culminating in the determination of isoelectric point (pI).
Isoelectric Point (pI)
- The pI is the pH at which a molecule has no net electrical charge.
- The formula for calculating pI is:
- pI = (pKa1 + pKa2) / 2, applicable for simple amino acids.
- For glycine, the pI is approximately 5.97, derived from its carboxyl (pKa ~2.34) and amino (pKa ~9.60) groups.
Uncommon Amino Acids
- Some posttranslational modifications yield uncommon amino acids, such as hydroxyproline and hydroxylysine found in collagen.
- Thyroxine is derived from tyrosine and is specific to the thyroid gland.
Examples of Titration & pI Calculations
- Example calculation for aspartic acid shows a net charge of -2 at high pH and the use of pKa values to establish pI.
- pI for basic amino acids like lysine is calculated by averaging the pKa of their basic side chains.
pKa Values
- A variety of amino acids have distinct pKa values, guiding their behavior in biological systems.
Charged vs. Uncharged State Ratios
- The ratio of charged to uncharged side chains, particularly for histidine with a pKa of 6.0, indicates that at pH 7.0, the ratio is approximately 10:1.
These notes encapsulate the essential characteristics and biochemical significance of amino acids and their roles in proteins.
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Description
Explore the key concepts of amino acids and peptides in this quiz based on Chapter 3. It covers the three-dimensional structures, properties of amino acids, peptide bonds, and the physiological activities of small peptides. Test your understanding of these fundamental biochemical elements.