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Questions and Answers
What is the charge of aspartic acid's side chain at physiologic pH?
What is the charge of aspartic acid's side chain at physiologic pH?
Which amino acids have side chains that are fully ionized and positively charged at physiologic pH?
Which amino acids have side chains that are fully ionized and positively charged at physiologic pH?
Which of the following amino acids is considered optically inactive?
Which of the following amino acids is considered optically inactive?
Which statement about the D and L forms of amino acids is true?
Which statement about the D and L forms of amino acids is true?
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At which pH does histidine's side chain have the potential to be positively charged?
At which pH does histidine's side chain have the potential to be positively charged?
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Which of the following amino acids can accept protons at physiologic pH?
Which of the following amino acids can accept protons at physiologic pH?
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What is the role of the red print in the representation of amino acids?
What is the role of the red print in the representation of amino acids?
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Which amino acid is a weak base and is largely uncharged at physiologic pH?
Which amino acid is a weak base and is largely uncharged at physiologic pH?
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What common structural feature do all proteins share?
What common structural feature do all proteins share?
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At physiologic pH (7.4), what form do the carboxyl and amino groups take in amino acids?
At physiologic pH (7.4), what form do the carboxyl and amino groups take in amino acids?
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Which type of amino acids has side chains that promote hydrophobic interactions in aqueous solutions?
Which type of amino acids has side chains that promote hydrophobic interactions in aqueous solutions?
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What is the role of the hydroxyl group in amino acids with uncharged polar side chains?
What is the role of the hydroxyl group in amino acids with uncharged polar side chains?
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Which amino acid is unique in having a secondary amino group?
Which amino acid is unique in having a secondary amino group?
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Which amino acids can lose a proton at alkaline pH?
Which amino acids can lose a proton at alkaline pH?
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What type of bonds are formed between the carboxyl and amino groups of amino acids in proteins?
What type of bonds are formed between the carboxyl and amino groups of amino acids in proteins?
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Amino acids with nonpolar side chains are primarily responsible for which phenomenon in proteins?
Amino acids with nonpolar side chains are primarily responsible for which phenomenon in proteins?
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Study Notes
Structure of Amino Acids
- Proteins are essential to living systems, they are linear polymers of amino acids.
- All amino acids, except proline, contain a carboxyl group, an amino group, and a specific side chain (R-group) attached to the α-carbon.
- Proline has a secondary amino group instead of the primary amino group found in other amino acids.
- At physiological pH (7.4), the carboxyl group ionizes to become negatively charged (COO-), while the amino group gains a proton and becomes positively charged (NH3+).
- In proteins, most carboxyl and amino groups form peptide bonds, limiting their participation in chemical reactions except for hydrogen bond formation.
Classification of Amino Acids
- Amino acids are classified by the polarity of their side chains:
- Nonpolar: Have even electron distribution, don't participate in hydrogen or ionic bonds.
- Polar: Have uneven electron distribution, can participate in hydrogen and ionic bonds.
Nonpolar Amino Acids
- Do not gain or lose protons.
- Promote hydrophobic interactions.
- In aqueous solutions, nonpolar amino acids cluster together in the protein's interior.
- This phenomenon, known as the hydrophobic effect, contributes to protein folding and stability.
Uncharged Polar Amino Acids
- Have no net charge at neutral pH, but some can lose protons at an alkaline pH.
- Serine, threonine, and tyrosine: Contain a hydroxyl group (OH-) that participates in hydrogen bonds.
- Asparagine and glutamine: Each contains a carbonyl group and an amide group capable of hydrogen bond formation.
Acidic Amino Acids
- Aspartic and glutamic acids are proton donors.
- At physiological pH, their side chains are fully ionized, forming negatively charged carboxylates (aspartate and glutamate).
Basic Amino Acids
- Side chains accept protons.
- At physiological pH, lysine and arginine are fully ionized, carrying a positive charge.
- Histidine is weakly basic and can be uncharged or positively charged at physiological pH depending on its environment within a protein.
Abbreviations and Symbols
- Each amino acid has a three-letter abbreviation and a one-letter symbol for convenience.
Optical Properties
- The α-carbon of an amino acid is chiral (except glycine) as it is attached to four different groups.
- Chiral carbons create two enantiomers: D and L, which are mirror images.
- Except for glycine, amino acids in proteins are always in the L-configuration.
- D-amino acids are found in some antibiotics and cell walls.
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Description
This quiz covers the fundamental structures and classifications of amino acids, essential building blocks of proteins. It includes information on their chemical properties, functional groups, and the differences between polar and nonpolar amino acids. Test your understanding of how these properties affect protein structure and function.
