PHYSICAL PROPERTIES
Solubility
Most of the amino acids are usually soluble in water and insoluble in organic solvents.
Melting point
Amino acids generally melt at higher temperatures, often above 200 Celsius.
Taste
Amino acids may be sweet (Gly,Ala,Val), tasteless (Leu) or bitter (Arg, Ile), Monosodium glutamate (MSG; ajinomotto) is used as flavouring agent in food industry.
Optical properties
All amino acids except glycine possess optical isomers due to the presence of asymmetric carbon atom. Some amino acids have a second asymmetric carbon e.g. isoleucine, threonine.
On heating to high temperatures, they decompose.
Amino acids are colourless, crystalline solid.
Peptide bond formation
Amino acids can connect with a peptide bond involving their amino and carboxylate groups.
Covalent bond formed between the alpha-amino group of one amino acid and an alpha-carboxyl group of other forming -CO-NH- linkage.
Peptide bonds are planar and partially ionic.
CHEMICAL PROPERTIES
ZITTERIONIC PROPERTY
A zwitterion is a molecule with functional groups, of which at least one has a positive and one has a negative electrical charge.
The net charge of the entire molecule is zero. Amino acids are the best-known examples of zwitterions.
They contain an amine group (basic) and a carboxylic group (acidic).
The -NH2 group is the stronger base, and so it picks up H+ from the -COOH group to leave a zwitterion.
The (neutral) zwitterion is the usual form amino acids exist in solution.
AMPHOTERIC PROPERTY
Amino acids are amphoteric in nature that is they act as both acids and base since due to the two amine and carboxylic group present.
NINHYDRIN TEST
When 1ml of Ninhydrin solution is added to a 1ml protein solution and heated, the formation of a violet colour indicates the presence of alpha-amino acids.
XANTHOPROTEIC TEST
The xanthoproteic test is performed for the detection of aromatic amino acids (tryosine, tryptophan, and phenylalanine) in a protein solution.
The nitration of benzoic radicals present in the amino acid chain occurs due to reaction with nitric acid, giving the solution yellow coloration.
REACTION WITH SANGER'S REAGENT
Sanger's reagent (1-fluoro-2,4-dinitrobenzene) reacts with a free amino group in the peptide chain in a mild alkaline medium under cold conditions.
REACTION WITH NITROUS ACID
Nitrous acid reacts with amino group to liberate nitrogen and form the corresponding hydroxyl.
FUNCTIONS OF AMINO ACIDS
In particular 20 very important amino acids are crucial for life as they contain peptides and proteins and are known to be the building blocks for all living things.
The linear sequence of amino acid residues in a polypeptide chain determines the three-dimensional configuration of a protein determines its function.
Amino acids are imperative for sustaining the health of the human body. The largely promote the:
- Production of hormones
- Structure of muscles
- Human nervous system's healthy functioning
- The health of vital organs
- Normal cellular structure
- The amino acids are used by various tissues to synthesize proteins and to produce nitrogen containing compounds (e.g., purines, heme, creatine, epinephrine) or they are oxidized to produce energy.
- The nitrogen- containing substrates are used in the biosynthesis of purines, pyrimidines, neurotransmitters, hormones, neurotransmitter, hormones, porphyrins, and non-essential amino acids.
Highlight main properties of amino acids
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