Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. Like leucine and isoleucine, valine is a branched-chain amino acid. In sickle-cell disease, a single glutamic acid in β-globin is replaced with valine.
Amino Acid Properties
| Amino Acid Name | 3-Letter Code | Side Chain Polarity |
|---|
| Threonine | Thr | Polar |
| Tryptophan | Trp | Nonpolar, aromatic |
| Tyrosine | Tyr | Polar, aromatic |
| Valine | Val | Nonpolar |
Annex 4 - Amino acids, one and three letter codes
| Amino acid | Three letter code | One letter code |
|---|
| alanine | ala | A |
| arginine | arg | R |
| asparagine | asn | N |
| aspartic acid | asp | D |
At the molecular level, basic dyes have amino groups, which are responsible for the molecule's positive charge. In short, the positively charged molecules of basic dyes bond to the negatively charged compounds in the materials with which these dyes are used.
An amino acid is an organic molecule that is made up of a basic amino group (−NH2), an acidic carboxyl group (−COOH), and an organic R group (or side chain) that is unique to each amino acid. Each molecule contains a central carbon (C) atom, called the α-carbon, to which both an amino and a carboxyl group are attached.
Two of the polar amino acids (lysine and arginine) contain amino functional groups and are therefore basic (positively charged). These two groups of amino acids (acidic and basic) are attracted to one another and can form electrostatic interactions.
At pH = 3.52, the H+ concentration is high (low pH = more acidic = more H+). Therefore the H+ will add to the carboxylate ion and neutralize the negative charge. The amino acid will have a positive charge on the amine group left and will have an overall charge of +1.
Structure of an Amino AcidEvery amino acid also has another atom or group of atoms bonded to the central atom known as the R group. This R group, or side chain, gives each amino acid proteins specific characteristics, including size, polarity, and pH.
Amino acids are usually classified by the properties of their side chain into four groups. The side chain can make an amino acid a weak acid or a weak base, and a hydrophile if the side chain is polar or a hydrophobe if it is nonpolar.
Generally, amino acids have the following structural properties:
- A carbon (the alpha carbon)
- A hydrogen atom (H)
- A Carboxyl group (-COOH)
- An Amino group (-NH2)
- A "variable" group or "R" group.
For most amino acids, zwitterions would be present at pH 7. Which is significant as, the physiological pH of the cells in our bodies is approximately 7.4. The amino acids in water would have the carboxy group unprotonated and the amino group protonated (zwitterion), and this is would be fluidly changing.
Members of the basic family of amino acids, like lysine, will also exhibit three pKa values. However, due to the extra amino group, they will have only one pKa in the acidic region and two pKa values in the basic region. The number of pKa values differentiates polar and nonpolar amino acids from charged amino acids.
An amino acid has this ability because at a certain pH value (different for each amino acid) nearly all the amino acid molecules exist as zwitterions. If acid is added to a solution containing the zwitterion, the carboxylate group captures a hydrogen (H+) ion, and the amino acid becomes positively charged.
Polar and charged amino acid residues (the remainder after peptide bond formation) are more likely to be found on the surface of soluble proteins where they can interact with water, and nonpolar (e.g., amino acid side chains) are more likely to be found in the interior where they are sequestered from water.
Seven amino acid side chains contain groups that ionize between pH 1 and 14. For Asp, Glu, Tyr, and Cys, the ionizable groups are uncharged below their pK and negatively charged above their pK. For His, Lys, and Arg, the ionizable groups are positively charged below their pK and uncharged above their pK.
All The 20 amino acids are classified into two different amino acid groups. Essential amino acids and Non-essential amino acids together make up the 20 amino acids. Out of the 20 amino acids, 9 are the essential amino acids, and the others are Non-essential amino acids.
There is one certain part of the structure of an amino acid that define it. It is called the R part. All amino acids are the same except this part.
You can calculate the net charge flow for a volume of space by calculating the total amount of charge entering and subtracting the total amount of charge leaving. Through electrons and protons that carry charge, charged particles can be created or destroyed to balance themselves out according to conservation of charge.
Isoelectronic point, pIThe isoelectronic point or isoionic point is the pH at which the amino acid does not migrate in an electric field. This means it is the pH at which the amino acid is neutral, i.e. the zwitterion form is dominant. A table of pKa and pI values can be found on the next page.
Among the 20 standard amino acids, the following are aromatic: phenylalanine, tryptophan and tyrosine. However, in addition to being aromatic, tyrosine can be classified as a polar amino acid.
Six amino acids are non-essential (dispensable) in humans, meaning they can be synthesized in sufficient quantities in the body. These six are alanine, aspartic acid, asparagine, glutamic acid, serine, and selenocysteine (considered the 21st amino acid).
Benzidine is not a amino acid while glycine, alanine and histidine are amino acid.
