Amino Acids

AMINO ACIDS

Amino acids are small molecules made of carbon, hydrogen, oxygen and nitrogen and in some cases also sulphur.

Each amino acid has a free amino group, a free carboxyl group and 'R' as side chain as same substituents on same carbon atom.

Amino group leads basic character while carboxylic group leads acidic character to the molecule.

Lysine and arginine are Basic Amino Acids because they carry two amino groups and one carboxylic group.

Glutamic acid (glutamate) and aspartic acid (aspartate) contain one amino and two carboxyl groups each and are classified as Acidic Amino Acids.

Alanine, glycine, valine are Neutral Amino Acids as these contain one amino and one carboxyl group each.

These are 20 different amino acids coded by our DNA that differ in the side chain.

Side chain of a basic and an acidic amino acid

Examples of polar and nonpolar amino acids

Most amino acids are laevo-rotatory while glycine is optically inactive.

There are three important non-protein amino acids.

They are ornithine, citrulline (both are involved in ornithine cycle to synthesise urea) and diaminopimelic acid.

A particular property of amino acids is the ionizable nature of -NH₂ and -COOH groups.

Hence, in solutions of different pH, the structure of amino acids changes.

 

B is called Zwitter ionic form

There are two types of amino acids viz. essential and non-essential amino acids.

Essential amino acids cannot be synthesized by animals whereas non-essential amino acids can be synthesised in animal's body.

There are seven essential amino acids in animals whereas 8 essential amino acids in man.

These are leucine, isoleucine, valine, tryptophan, phenylalanine, lysine and methionine.

Threonine is an additional essential amino acid in human beings.

Two amino acids viz. arginine and histidine are semi-indispensable amino acids as they can be synthesised by human beings but very slowly.

Differences between Essential and Nonessential Amino Acids

Concept Builder

Amino acids are classified into following groups :

(i) Neutral amino acid: With one -NH₂ and one -COOH group e.g. glycine, alanine (non-polar).

(ii) Acidic amino acid: Have an extra COOH group (monoamino dicarboxylic), e.g. glutamic and aspartic acid.

(iii) Basic amino acid: Have additional NH₂ group (diamino monocarboxylic) e.g. arginine, lysine.

(iv) Sulphur containing amino acid: Have sulphur e.g. cysteine, cystine and methionine.

(v) Alcoholic amino acid: Have -OH group e.g. serine, threonine.

(vi) Aromatic amino acid : Have cyclic structure having a side chain with -COOH and NH₂ groups e.g. phenyl alanine, tryptophan, tyrosine.

(vii) Heterocyclic amino acid: N is present in the ring e.g. proline, histidine, hydroxyproline.

(viii) Semi essential amino acid : Arginine and histidine are semi-essential amino acids required by children.

Protein amino acids are laevorotatory and -type except glycine. (Glycine: Simplest amino acid, involved in the formation of heme).

Functions of Amino Acids

Besides their principal function as building blocks for proteins, specific amino acids are also converted into different types of biologically active compounds.

For example, tyrosine is converted into the hormones thyroxine and adrenaline, as well as the skin pigment melanin, glycine is involved in the formation of heme and tryptophan in the formation of the vitamin nicotinamide as well as the plant hormone indole-3-acetic acid.

After the removal of the amino group the carbon chain of many amino acids is converted into glucose.

On losing the carboxyl groups as carbon dioxide, amino acids form biologically active amines such as histamine. Histamine is required for the functioning of muscles, blood capillaries and gastric juices.

Ornithine and citrulline are components of urea cycle.

Antibiotics contain non protein amino acids.

Amino acids form organic acids which form glucose by gluconeogenesis.

Lysine is an essential amino acid because it is not formed in the body and has to be provided through diet.

Amino Acids

Amino acids are chemical molecules with amino and carboxylate functional groups as well as a side chain that is unique to each amino acid. Amino Acids are chemical substances that combine to produce proteins, which is why they are known as the building blocks of proteins. These biomolecules have a role in a variety of biological and chemical functions in the human body and are essential for human growth and development. There are around 300 amino acids found in nature. Amino acids' general features include:

1. A high melting and boiling point.

2. Amino acids are crystalline solids that are white in color.

3. Few amino acids have a pleasant, tasteless, or bitter flavour.

4. The majority of amino acids are water-soluble and insoluble in organic solvents.

There are 20 amino acids found in nature, all of which have the same structural features: an amino group (-NH3+), a carboxylate group (-COO-), and a hydrogen-bonded to the same carbon atom. Their side-chain, known as the R group, distinguishes them from one another. The - carbon of each amino acid is connected to four distinct groups namely: Amino group, COOH, Hydrogen atom, and Sidechain.

Amino acids have a general structure which can be represented as:

 

Our bodies can easily produce a few non-essential amino acids out of a total of 20 amino acids. Alanine, asparagine, arginine, aspartic acid, glutamic acid, cysteine, glutamine, proline, glycine, serine, and tyrosine are examples of these amino acids.

Besides these, there are nine other amino acids that are extremely important because our bodies cannot make them. Isoleucine, histidine, lysine, leucine, phenylalanine, tryptophan, methionine, threonine, and valine are examples of important amino acids.

Amino acids are essential for a variety of biological and chemical tasks in our bodies, including tissue construction and repair, enzyme production and activity, food digestion, molecule transportation, and so on. Only a few amino acids can be synthesized by our bodies, thus the rest, known as essential amino acids, must be obtained from protein-rich foods in our daily diet. Plant-based foods with high levels of amino acids include broccoli, beans, beets, pumpkin, cabbage, almonds, dry fruits, chia seeds, oats, peas, carrots, cucumber, green leafy vegetables, onions, soybeans, whole grain, peanuts, legumes, lentils, and so on. Apples, bananas, berries, figs, grapes, melons, oranges, papaya, pineapple, and pomegranates are high in amino acids.Dairy products, eggs, seafood, poultry, beef, pork, and other animal products are examples of other animal goods.

Functions of Essential Amino acids

1. Phenylalanine helps in maintaining a healthy nervous system and in boosting memory power.

2. Valine acts as an important component in promoting muscle growth.

3. Threonine helps in promoting the functions of the immune system.

4. Tryptophan is involved in the production of vitamin B3 and serotonin hormones. This serotonin hormone plays a vital role in maintaining our appetite, regulating sleep and boosting our moods.

5. Isoleucine plays a vital role in the formation of hemoglobin, stimulating the pancreas to synthesize insulin, and transporting oxygen from the lungs to the various parts.

6. Methionine is used in the treatment of kidney stones, maintaining healthy skin and also used in controlling invade of pathogenic bacteria.

7. Leucine is involved in promoting protein synthesis and growth hormones.

8. Lysine is necessary for promoting the formation of antibodies, hormones, and enzymes and in the development and fixation of calcium in bones.

9. Histidine is involved in many enzymatic processes and in the synthesizing of both red blood cells (erythrocytes) and white blood cells (leukocytes).

Functions of Non-Essential Amino acids

1. Alanine functions by removing toxins from our body and in the production of glucose and other amino acids.

2. Cysteine acts as an antioxidant and provides resistance to our body; it is important for making collagen. It affects the texture and elasticity of the skin

3. Glutamine promotes a healthy brain function and is necessary for the synthesis of nucleic acids – DNA and RNA.

4. Glycine is helpful in maintaining the proper cell growth, and its function, and it also plays a vital role in healing wounds. It acts as a neurotransmitter.

5. Glutamic acid acts as a neurotransmitter and is mainly involved in the development and functioning of the human brain.

6. Arginine helps in promoting the synthesis of proteins and hormones, detoxification in the kidneys, healing wounds, and maintaining a healthy immune system.

7. Tyrosine plays a vital role in the production of the thyroid hormones -T3 and T4, in synthesizing a class of neurotransmitters and melanin, which are natural pigments found in our eyes, hair, and skin.

8. Serine helps in promoting muscle growth and in the synthesis of immune system proteins.

9. Asparagine is mainly involved in the transportation of nitrogen into our body cells, formations of purines and pyrimidine for the synthesis of DNA, the development of the nervous system and improving our body stamina.

10. Aspartic acid plays a major role in metabolism and in promoting the synthesis of other amino acids.

11. Proline is mainly involved in the repairing of the tissues and the formation of collagen, preventing the thickening and hardening of the walls of the arteries (arteriosclerosis) and in the regeneration of new skin.