**1. Amino Acid Discovery and Structure:**
– Amino acids were first discovered in the early 1800s.
– Asparagine was the first amino acid discovered in 1806.
– Various amino acids were discovered in subsequent years, with threonine being the last common amino acid found in 1935.
– Amino acids have amino and carboxylic acid groups.
– Proteins are made of amino acid residues.
– Ribosomes assemble peptides and proteins from 22 proteinogenic amino acids.
**2. Amino Acid Properties and Special Cases:**
– Amino acids have unique properties based on their side chains.
– Special case side chains like glycine, cysteine, and tyrosine have distinct impacts on protein folding and function.
– Disulfide bonds formed by cysteines influence protein folding and stability.
– Proline’s structure uniquely impacts protein structure.
– Selenocysteine participates in unique enzymatic reactions.
**3. Amino Acid Behavior and Zwitterions:**
– Amino acids exist as dipolar ions in aqueous solutions.
– Amino acids exhibit Brønsted acid-base behavior.
– Isoelectric point is where the net charge of amino acids is zero.
– Zwitterions have minimum solubility at their isoelectric point.
– Amino acids have distinct behavior at extreme pH levels.
**4. Physicochemical Properties and Standard Abbreviations:**
– Amino acids’ physicochemical properties influence protein structure and interactions.
– Various hydrophobicity scales exist for amino acid residues.
– Amino acid abbreviations provide a standardized way to represent amino acids.
– Amino acid properties are crucial for understanding protein structure.
– Standard amino acid abbreviations are used for genetic coding.
**5. Occurrence, Functions, and Evolution of Amino Acids:**
– Amino acids are the precursors to proteins and are crucial for various biological functions.
– The 20 amino acids encoded by the universal genetic code are standard.
– Selenocysteine and pyrrolysine are incorporated by unique mechanisms.
– Evolutionary studies suggest distinct groupings of amino acids based on their roles in the early genetic code.
– Mnemonics are used to aid in remembering amino acids.
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 appear in the genetic code of life.
Amino acids can be classified according to the locations of the core structural functional groups (alpha- (α-), beta- (β-), gamma- (γ-) amino acids, etc.), other categories relate to polarity, ionization, and side chain group type (aliphatic, acyclic, aromatic, polar, etc.). In the form of proteins, amino acid residues form the second-largest component (water being the largest) of human muscles and other tissues. Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis. It is thought that they played a key role in enabling life on Earth and its emergence.
Amino acids are formally named by the IUPAC-IUBMB Joint Commission on Biochemical Nomenclature in terms of the fictitious "neutral" structure shown in the illustration. For example, the systematic name of alanine is 2-aminopropanoic acid, based on the formula CH3−CH(NH2)−COOH. The Commission justified this approach as follows:
The systematic names and formulas given refer to hypothetical forms in which amino groups are unprotonated and carboxyl groups are undissociated. This convention is useful to avoid various nomenclatural problems but should not be taken to imply that these structures represent an appreciable fraction of the amino-acid molecules.