Skip to main content
Chemistry LibreTexts

1.1: Nomenclature of Amino acids

  • Page ID
    165252
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Common amino acids

    There are 20 common amino acids. They are composed of C, H, O, N and S atoms. They are structurally and chemically different, and also differ in size and volume. Some are branched structures, some are linear, some have ring structures. One of the 20 common amino acids is actually an imino acid. A typical grouping of their chemical nature is as follows:

    • Nonpolar (hydrocarbons and one sulfur-containing amino acid). Dispersion forces and hydrophobic effects predominate in their interactions. They cannot H-bond with water and these side chains have a characteristic hydrophobic effect in water.
    • Polar uncharged. Contain functional groups that can H-bond with water and other amino acids. Include C, H, O, N and S atoms.
    • Acidic. Contain a carboxylic acid functional group with a negative charge at neutral pH. Can H-bond with water, can form ionic interactions, and can also serve as nucleophiles or participate in acid-base chemistry.
    • Basic. Nitrogen containing bases (e.g. guanidino, imidazole or amino groups) with a net positive charge at neutral pH. Can serve as proton donors in chemical reactions, and form ionic interactions.

    The amino acids have a name, as well as a three letter or single letter mnemonic code:

    Type Name R-group Structure
    Nonpolar

    Leucine

    Leu, L

    leu.jpg
     

    Isoleucine

    Ile, I

    Ile.jpg
     

    Valine

    Val, V

    val.jpg
     

    Alanine

    Ala, A

    ala.jpg
     

    Methionine

    Met, M

    met.jpg
     

    Phenylalanine

    Phe, F

    phe.jpg
     

    Tryptophan

    Trp, W

    trp.jpg
     

    Proline

    Pro, P

    pro.jpg
     

    Glycine

    Gly, G

    (note: sometimes included in polar group)

    gly.jpg
    Polar, uncharged

    Serine

    Ser, S

    ser.jpg
     

    Asparagine

    Asn, N

    asn.jpg
     

    Glutamine

    Gln, Q

    Glutamine.gif
     

    Threonine

    Thr, T

    thr.jpg
     

    Cysteine

    Cys, C

    cys.jpg
     

    Tyrosine

    Tyr, Y

    tyr.jpg
    Acidic

    Aspartic acid

    Asp, D

    asp.jpg
     

    Glutamic acid

    Glu, E

    glu.jpg
    Basic

    Lysine

    Lys, K

    lys.jpg
     

    Arginine

    Arg, R

    arg.jpg
     

    Histidine

    His, H

    his.jpg

    Uncommon amino acids

    In addition to the 20 common amino acids, there are several uncommon ones found:

    • Hydroxylysine and hydroxyproline. These are found in the protein collagen. Collagen is a fibrous protein made up of three polypeptides that form a stable assembly, but only if the proline and lysine residues are hydroxylated. (requires vitamin C for reduction of these amino acids to hydroxy form)
    • Thyroxine, an iodinated derivative of tyrosine, found in thyroglobulin (produced by thyroid gland; requires iodine in diet)
    • g-carboxyglutamic acid (i.e. glutamic acid with two carboxyl groups) found in certain blood clotting enzymes (requires vitamin K for production)
    • N-methyl arginine and n-acetyl lysine. Found in some DNA binding proteins known as histones

    Amino acid derivatives not found in proteins

    Some amino acids are made that are not intended for incorporation into proteins, rather they have important functionalities on their own

    1. Serotonin (derivative of tryptophan) and g-amino butyric acid (a derivative of glutamic acid) are both neurotransmitters
    2. Histamine (derivative of histidine) involved in allergic response
    3. Adrenaline (derivative of tyrosine) a hormone
    4. Various antibiotics are amino acid derivatives (penicillin)

    The Essential Amino Acids

    Humans must include adequate amounts of 9 amino acids in their diet.

    • Histidine
    • Isoleucine
    • Leucine
    • Lysine
    • Methionine (and/or cysteine)
    • Phenylalanine (and/or tyrosine)
    • Threonine
    • Tryptophan
    • Valine

    These "essential" amino acids cannot be synthesized from other precursors. However, cysteine can partially meet the need for methionine (they both contain sulfur), and tyrosine can partially substitute for phenylalanine. Two of the essential amino acids, lysine and tryptophan, are poorly represented in most plant proteins. Thus strict vegetarians should ensure that their diet contains sufficient amounts of these two amino acids. 19 of the 20 amino acids listed above can exist in two forms in three dimensions.

    Contributors

    Thumbnail: 3D model of L-tryptophan. Image used with permission (Public Domain; Benjah-bmm27).


    1.1: Nomenclature of Amino acids is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

    • Was this article helpful?