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Questions and Answers
What type of amino acids are aspartic acid and glutamic acid?
Lysine and arginine are positively charged at physiological pH.
True
Name two examples of essential amino acids.
Isoleucine, Leucine
Histidine and arginine are considered ______ amino acids.
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What characterizes amino acids that have asymmetric centers at the α-carbon?
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Glycine has optical activity because it has a symmetric carbon.
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Briefly explain the role of buffers in amino acids.
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The replacement of glutamic acid with ______ in sickle cell anemia leads to hydrophobic properties.
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Match the following amino acids with their classification:
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All amino acids found in proteins are of the D-configuration.
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Which amino acids are classified as having nonpolar side chains?
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All amino acids have polar side chains and are hydrophilic in nature.
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What are the two classifications of amino acids based on essentiality?
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Amino acids with ______ side chains are hydrophilic and can form glycoproteins.
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Match the following amino acids with their characteristics:
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Which amino acid is commonly referred to as an imino acid?
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Amino acids with acidic side chains have a net positive charge at neutral pH.
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What characterizes the optical properties of amino acids?
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In a polar environment, nonpolar amino acids are found in the ______ of the protein.
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Which amino acids belong to the group of hydrophilic amino acids with uncharged polar side chains?
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Study Notes
Amino Acid Chemistry
- There are over 300 amino acids found in nature, but only 20 are commonly found in mammalian proteins.
- Amino acids are the building blocks of proteins.
- Amino acids are classified according to the properties of their side chains.
Amino Acid Classification by Side Chain Properties
- Nonpolar side chains: Hydrophobic and lipophilic. These amino acids cluster together in the interior of proteins in aqueous solutions. In hydrophobic environments like membranes, they are found on the protein's outer surface. This group includes Glycine, Alanine, Valine, Leucine, Isoleucine, Phenylalanine, Tryptophan, Methionine, Proline.
- Uncharged polar side chains: Hydrophilic and have a zero net charge at neutral pH. These amino acids can bind to oligosaccharides to form glycoproteins and to phosphate groups to form phosphoproteins. This group includes Serine, Threonine, Tyrosine, Asparagine, Glutamine, and Cysteine.
- Acidic side chains: Hydrophilic and negatively charged at physiological pH. These amino acids act as proton donors. This group includes Aspartic acid and Glutamic acid.
- Basic side chains: Hydrophilic and positively charged at physiological pH. These amino acids act as proton acceptors. This group includes Arginine, Lysine, and Histidine.
Proline
- Proline is often referred to as an imino acid.
- Proline's unique geometry contributes to the formation of collagen's fibrous structure and can interrupt α-helices in globular proteins.
Clinical Significance of Amino Acid Properties
- In Sickle Cell Anemia, the 6th amino acid in the beta chain of hemoglobin (HbS) is replaced by valine. This change replaces a hydrophilic glutamic acid with a hydrophobic valine.
Amino Acid Classification by Nutritional Requirement
- Essential or Indispensable: These amino acids cannot be synthesized by humans and must be obtained from the diet. This group includes Isoleucine, Leucine, Threonine, Lysine, Methionine, Phenylalanine, Tryptophan, and Valine.
- Nonessential or Dispensable: These amino acids can be synthesized by metabolic pathways in the body. This group includes Aspartic acid, Glutamic acid, Glycine, Alanine, Proline, Serine, Cysteine, Tyrosine, Glutamine, and Asparagine.
- Partially Essential or Semi-Essential: These are required in the diet of growing children but are not essential for adults. This group includes Histidine and Arginine.
Optical Properties of Amino Acids
- Amino acids with an asymmetric center at the α-carbon exist in two forms: D and L. These are termed stereoisomers, optical isomers, or enantiomers.
- All amino acids found in proteins are of the L-configuration. D-amino acids are found in some antibiotics and in plant and bacterial cell walls.
- Glycine is the only amino acid that does not have optical activity because it has a symmetric carbon.
Acidic and Basic Properties of Amino Acids
- Amino acids in an aqueous solution contain weakly acidic α-carboxyl groups and weakly basic α-amino groups.
- This allows free amino acids and amino acids within peptide linkages to act as buffers.
- Buffers resist changes in pH following the addition of an acid or base.
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Description
This quiz tests your knowledge on amino acids, their classifications, and properties. Learn about the distinct groups of amino acids based on their side chain characteristics, including nonpolar, uncharged polar, and acidic side chains. Dive into the fascinating world of protein building blocks!
