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Questions and Answers
What is the general structure of an amino acid?
Which amino acid has a secondary amine instead of a primary amine at the α-position relative to the carboxyl group?
Which stereoisomer configuration are all amino acids derived from proteins in terms of their α-C atoms?
Which type of amino acids are classified based on polarity?
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Why is glycine considered achiral in terms of its stereochemistry?
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What instrument is used to measure the direction and angle of rotation of polarized light by amino acids?
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What is unique about cysteine among the 20 amino acids?
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What is the metabolic fate of glucogenic amino acids?
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Why are nonpolar side chains in polypeptides associated with each other rather than with water?
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Which type of amino acid cannot be synthesized within the human body?
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What structural feature allows cysteine to form disulfide bonds?
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What is the metabolic fate of ketogenic amino acids?
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Which of the following amino acids is classified as an uncommon amino acid?
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What is the correct order of amino acids in the pentapeptide Ser-Gly-Tyr-Ala-Leu?
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What type of bond is formed between two amino acids in a peptide?
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Which of the following amino acids is a derivative of tyrosine and plays a role in regulating metabolism?
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What is the stereochemistry of the α-carbon in amino acids?
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What is the three-letter abbreviation for the amino acid leucine?
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Study Notes
Amino Acid Structure
- Amino acids are composed of a carboxyl group (COOH), an É‘-amino group (NH2), and a side chain (R) that affects the protein's 3D structure and characteristics.
- Except for proline, all 19 proteinogenic amino acids have a primary amine at the É‘-position relative to the carboxyl group.
Stereochemistry of Amino Acids
- All amino acids recovered from polypeptides, except glycine, are optically active, meaning they rotate the plane of polarized light.
- The α-C atoms of amino acids (except glycine) are asymmetric centers, making them optically active.
- Glycine is not optically active because it has two H atoms attached to its α-C atom, making it superimposable on its mirror image.
Classification of Amino Acids
- Amino acids can be classified based on polarity (non-polar, polar uncharged, and polar charged).
- They can also be classified based on chemical behavior of the side chain (aromatic, aliphatic, basic, or acidic).
- Amino acids can be classified as essential or non-essential based on nutrition.
- They can also be classified based on metabolic fate (glucogenic and ketogenic).
Neutral, Basic, and Acidic Amino Acids
- Neutral amino acids are classified based on their side chain properties.
- Basic amino acids have a positive charge, while acidic amino acids have a negative charge.
- Cysteine is unique due to its thiol group, which can form a disulfide bond with another cysteine.
Essential and Non-Essential Amino Acids
- Essential amino acids cannot be synthesized in the human body and must be present in the diet.
- Non-essential amino acids can be synthesized in the body.
- Some amino acids are required to some degree in young, growing animals and/or during illness.
Glucogenic and Ketogenic Amino Acids
- Amino acids degraded to pyruvate, α-ketoglutarate, succinyl CoA, fumarate, and/or oxaloacetate can be converted to glucose and glycogen, making them glucogenic.
- Other amino acids are ketogenic, meaning they are degraded to acetyl CoA or acetoacetate.
Uncommon Amino Acids
- Citrulline is a non-proteinogenic amino acid that plays a role in the urea cycle.
- Other uncommon amino acids include neurotransmitters and hormones, such as thyroxine.
Peptide Structure
- A peptide bond is formed by condensation, linking two amino acid molecules through a substituted amide linkage.
- Peptides can be displayed with the amino-terminal end on the left and the carboxyl-terminal end on the right.
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Description
Test your knowledge on the structure of amino acids, the building blocks of proteins. Learn about the components such as carboxyl group, É‘-amino group, and side chains, as well as the general structure and stereochemistry of amino acids.
