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# Glycine

Organic compounds containing an carboxylic acid group and amine group are called as amino acids. They are the backbones of proteins. They are classified as essential and non essential amino acids.

The amino acids which are synthesized in our body are not required in our diet and they are called as non essential amino acids. Glycine is an example of such a type of amino acids. Some of the amino acids are not synthesized in our body and has to be supplied through diet regularly for proper metabolic activity. They are called as essential amino acids. Isoleucine is an example for essential amino acid.

Amino acids function both as acid and base and the pH at which the acid and basic strength are equal is called as isoelectric point for such amino acid. In isoelectric point the amino acid ion will not move towards electrodes. The ionized form of an amino acid is called as zwitter ion.
The pKa value of the amino acid is determined by the number of NH2 group and COOH group along with some basic side chain like imidazole. Hence some of amino acids will be neutral while some are basic in nature. Similarly the long hydrophobic aromatic ring or aliphatic chain will make the amino acid insoluble in water. Hence they are classified as water soluble and water insoluble amino acids.

## Glycine Amino Acid

Glycine is the simplest amino acid which is non essential and is produced within our body. The formula of glycine is NH2-CH2-COOH. The structure of glycine is given below.

It is colorless, sweet tasting solid. It is unique among other amino acids as it is alone optically inactive. It can dissolve both water and other organic solvents as it is having both hydrophobic and hydrophilic properties.

## d-Glycine

Compounds containing asymmetric carbon are optically active. They will rotate the plane polarized light in specific direction. The compounds that rotate the plane polarized light in the clockwise direction are called as dextro rotatory. The are prefixed by 'd' before their name.

Similarly the compounds that rotate the plane polarized light in the anti clockwise direction are called laevo rotatory. They are prefixed by 'l' before their name. A pair of dextro rotatory and laevo rotatory compounds with same molecular formula and structure with different in direction of rotation of plane polarized light are called as enantiomers.

But glycine is symmetric as it contains two hydrogen atoms attached to the same carbon atom. Hence it is optically inactive. Hence the convention of mentioning d-glycine or l-glycine is irrelevant in glycine.

## l-Glycine

There is another way of representing the optically active compounds. This method is based on the orientation of hydrogen and OH group around the last carbon atom with respect to configuration of glyceraldehyde.

Hence, the compounds having the same configuration of D glyceraldehyde are called as D isomers and the other enantiomer is called as L isomer. But as glycine is optically inactive. Hence the naming of glycine like D-glycine or L-glycine is irrelevant.

## Glycine Molecular Weight

Glycine molecular weight is determined by osmotic pressure and other experiments like elevation of boiling point and depression of freezing point. The molecular formula of glycine is C2H5NO2. The corresponding molecular mass of glycine is 75.066 g/mol

## Glycine Structure

In the structure of glycine the central carbon atom is sp3 hybridized with tetrahedral shape. To this carbon atom one carboxylic acid group, two hydrogen atoms and one amine group are attached.

Hence, the structure of glycine shows that it contains both carboxylic acid and amine group in the same carbon atom. This is important category of amino acids called as $\alpha$-amino acids.

## Glycine Preparation Method

It is industrially prepared by the reaction of chloro acetic acid with ammonia.

ClCH2COOH + 2 NH3 → H2NCH2COOH + NH4Cl

It is non essential amino acid as it is synthesized from another amino acid, serine. Similarly it is synthesized in the liver of vertebrates.

## Properties of Glycine

The pKA values of glycine are 2.35 and 9.78, and hence it will be in anionic form above pH 9.78, with formula H2NCH2CO2-. Similarly below pH 2.35, the solution contain the cationic carboxylic acid H3N+CH2CO2H. The isoelectric point is 6.06.

Glycine exists in zwitterionic form in solution. The structure of zwitter ion will change in according to the pH of the solution as given above. The general structure of zwitter ion is given below.

In our body the glycine is degraded in any of the following ways.

1. In most of the plants and animals it is degraded using glycine cleavage enzyme. In this reaction NADH is produced.
2. In the second way the glycine is degraded again back to serine. Serine is further degraded to pyruvate by another enzyme called serine dehydradase.

The half life of glycine in human body is estimated around 0.5 to 4.0 hours.

## Glycine Uses

1. Glycine is the starting material for many other proteins and amino acids.
2. It is a neuro transmitter in retina, spinal cord and brain stem.
3. It is an additive in animal feeds and pet feeds.
4. It is used as sweet enhancer. It is also used along with drugs to improve the absorption of drug in the stomach.
5. In medicines it is used as buffering agent in certain type like antacids, analgesics and cosmetics.
6. It is used in the preparation of herbicide glyphosate.
7. It is used to treat stroke, BPH, schizophrenia. It is also used to protect the kidneys after kidney transplantation. Similarly it is also used to protect the liver from harmful toxic materials.
All the protein substances like pulses, meat are rich source of glycine. Regular intake of glycine is essential to
1. Induce the growth and regeneration of new cells and thereby increases muscle strength.
2. Slow muscle breakdown and increases the healing effect after injury.
3. Control blood sugar level and to optimize the use of ATP.
4. Calm the brain and induce rest/sleep.
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