Amino acid: Brief overview

Proteins have an amazing range of structural and catalytic properties as a result of  their varying amino acid composition. Because of this versatility, proteins serve an astonishing variety of functions in living organisms.

Amino acids are the building blocks of proteins; they contain a carboxylic acid group and an amino group on the alpha (α) carbon, the carbon adjacent to the C=O; because they have both a weak acid and weak base present, they actually exist as a salt.

Amino acids play major role in regulating multiple processes related to gene expression, including modulation of the function of the proteins that mediate messenger RNA (mRNA) translation.

The physical and chemical properties of a protein are determined by its constituent amino acids. The individual amino acid subunits are joined by amide linkages called peptide bonds.

The simplest acid is α-amino acetic acid, called glycine. Other common amino acids have side chains (symbolized by R) substituted on the carbon atom. For example, alanine is the amino acid with a methyl side chain.

Unlike most organic compounds, amino acids are soluble in water, have either high melting points or decompose upon heating. They act more like inorganic materials than organic compounds.

The standard amino acids are 20 common α-amino acids that are found in nearly all  proteins. The standard amino acids differ from each other in the structure of the side chains bonded to their carbon atoms. All the standard amino acids are L-amino acids.

Based on their nutritional/physiological roles, amino acids can be differentiated as:
• Essential amino acids: Valine, leucine, isoleucine, phenylalanine, tryptophan, methionine, threonine, histidine (essential for infants), lysine and arginine (“semi-essential”).
• Nonessential amino acids: Glycine, alanine, proline, serine, cysteine, tyrosine, asparagine, glutamine, aspartic acid and glutamic acid.

Amino acids are utilized in formation of protein. If amino acids are deficient, then protein synthesis does not occur. As a result, protein deficiency disease may occur. It is necessary to take balanced diet containing all essential amino acids.
Amino acid: Brief overview

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Basic structure of protein

The word protein is derived from Greek word, “proteios” which means primary. As the name shows, the proteins are of paramount importance for biological systems.

Amino acids are the building blocks of proteins. Amino acids can combine to form long linear chains known as polypeptides. Proteins are nothing more than long polypeptide chains.

Proteins are synthesized by polymerization of amino acids through peptide bonds. Two amino acids combined to form a dipeptide; three amino acids form a tripeptide; four will make a tetrapeptide; a few amino acids together will make an oligopeptide; and combination of 10-50 amino acids is a polypeptide.

Chains that are less than 40-50 amino acids or residues are often referred to as polypeptide chains since they are too small to form a functional domain. Larger than this size, they are called proteins.

Most organisms use 20 naturally-occurring amino acids to build proteins. The linear sequence of the amino acids in a protein is dictated by the sequence of the nucleotides in an organisms’ genetic code.

Proteins come in various sizes and shapes. Those with thread-like shapes, the fibrous proteins, tend to have structural or mechanical roles. Those with spherical shapes, the globular protein, function as enzymes, transport proteins, or antibodies. Fibrous proteins tend to be water-insoluble while globular protein’s tend to be water soluble.

The structure, function and general properties of a protein are all determined by the sequence of amino acids that make up its primary sequence.

Proteins are used for body building; all the major structural and functional aspects of the body are carried out by protein molecules. Abnormality in protein structure will lead to molecular diseases with profound alterations in metabolic functions.
Basic structure of protein

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General description of protein

Protein is one of the nutrients along with carbohydrate, fat, vitamins, minerals, and water.

Proteins are single, unbranched chains of amino acid monomers. Amino acids are the building blocks of proteins. There are 20 different naturally occurring amino acids. The amino acid side chains in a peptide can become modified, extending the functional repertoire of amino acids to more than hundred different amino acids. A protein’s amino acid sequence determines its three-dimensional structure.

To make a protein, these amino acids are joined together in a polypeptide chain through the formation of a peptide bond.

Chains that are less than 40-50 amino acids or residues are often referred to as polypeptide chains since they are too small to form a functional domain. Larger than this size, they are called proteins.

Humans can synthesize 12 (nutritionally nonessential) of the 20 common amino acids from the amphibolic intermediates of glycolysis and of the citric acid cycle. Of the 12 nutritionally nonessential amino acids, nine are formed from amphibolic intermediates and three (cysteine, tyrosine and hydroxylysine) from nutritionally essential amino acids. Protein is an essential nutrient. There is no life without protein.

Protein is contained in every part of human body, the skin, muscles, hair, blood, body organs, eyes, even fingernails and bone. Next to water, protein is the most plentiful substance in human body.

Protein has a critical physiological function. Protein is primarily used in the body to build, maintain, and repair body tissues. In the event that protein intake is greater than that required by the body for this primary function, excessive protein is converted to energy for immediate use or stored in the body as fat.
General description of protein

General structure of an amino acid

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Chemistry of theanine

Theanine is a unique free amino acid found only in tea leaves. It is one of the important chemical components that contribute to the taste of green tea infusion.

Green flavor has four characteristic taste elements: bitterness, astringence, sweetness and umami (a brothy or savory tatse). The brothy, sweet, umami taste is due to amino acids, especially theanine. Theanine has two enantiomers: L- and D-theanine. The average level of D-theanine was around 1.85% of the total theanine.

Theanine is the analogue of glutamine. Theanine is found in every part of the tea except for the fruit and contributes the major part of amino acids in tea.

Structure of theanine

It was detected by Japanese researchers as an unknown compound but the major one in the amino acid fraction of tea and was named theanine. Later, it was isolated and finally identified to be N-ethylglutamic acid.
Chemistry of theanine

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What is tyramine?

Tyramine is an amino acid that is created during the breakdown of a protein. It is formed by decarboxylation of tyrosine. That breakdown occurs as food is ripened, dried, fermented, cured, pickled, canned or preserved.

In ripened cheese, tyramine, putrescine and cadaverine predominate, while tyramine is found in higher concentrations (up to 150 mg/100 g) than other amines in fermented meats.

Other foods containing tyramine: eggplants, avocados, bananas, broad beans, chicken liver, peanuts, raspberries, red plum, sour cream and tomatoes.

Tyramine is naturally produced in the human gallbladder. Tyramine has been associate with hypertension and headache in sensitive individuals, especially those who suffer from migraine headaches. In migraine sufferers, there is a buildup of tyramine that the body cannot break down on its own.

Migraine sufferers are deficient in the enzyme Roboflavin-5-Phosphate. With this deficiency, the body goes into attack mode and blood pressure rises, causing swelling of the blood vessel that surround the cranial cavity, causing the beginnings of the feared migraine.
What is tyramine?

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Gluten protein

Gluten is a protein that appears in foods processed from wheat and other cereal grains, including barley and rye.

It is the mixture of proteins in the endosperm of cereals. It gives elasticity to dough, helping it to rise and keep it shape and often giving the final product a chewy texture.

Gluten when dried and milled to powder and added to ordinary flour dough, improves rising and decreases the bread’s structural stability and chewiness. It is gluten that is responsible for the appearance texture and volume of dough.

Mixing and kneading activate the gluten; the more the dough is kneaded the more the gluten develops, reinforcing the structure of the dough.

There are two main groups of proteins in gluten, called the prolamin (gliadins) and glutelin (glutenins) and are regarded as storage proteins.

The amino acid composition of the protein varies; for example, lysine concentration is about three times higher in glutelin than in prolamin.

Wheat gluten contains high concentration of the amino acids glutamic acid and proline (33% and 12% of total amino acids, respectively).
Gluten protein

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Properties of amino acids

The amino acids are the fundamentals units of protein structure.  Amino acids are all characterized by the presence of an amino (NH2) group with basic properties and a carboxyl (COOH) group with acidic properties attached to the same carbon atom.

Most naturally occurring amino acids are of the L-configurations, although D-amino acids are not uncommon in some microorganisms.

In the formation of a protein, amino acids are linked together by the peptide linkage in which the basic (amino) group of one amino acid is linked to the carboxyl group of another, with the elimination of a molecule of water.

Amino acid crystals are generally white. All crystalline amino acid, except for glutamine and cysteine have a high melting point of more than 200 ° C. Glutamine and cysteine have melting point of 185 ° C and 178 °C respectively.

In solution, at physiologic pH, the free amino acids exist as zwitterions, ions in which the amino group is positively charged and the carboxylate group is negatively charged.
Properties of amino acids

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Food sources of arginine

Arginine, a benign amino acid, increases nitric oxide; in high doses it acts as a vasodilator.

The average American generally ingests up to 5.4 g of L-arginine per day through foods. This amount is generally more than adequate to serve as a substrate for nitric oxide synthesis.

The richest sources of arginine are found in vegetable protein.

Nuts especially peanuts are the best source of arginine, an amino acid that plays and important role in wound healing, detoxification reactions, immune functions, and promotion of the secretion of several hormones, including insulin and growth hormone. Peanuts contain 3 g arginine per 100 g.

Food sources other than nuts are including meats, seafood, eggs, dairy products, chocolate, and gelatin. 

Arginine is high in oats, wheat and rice than other amino acids.
Food sources of arginine

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Amino acid: the basic structure of proteins

Amino acid is the name given to the basic structural unit of proteins. Nitrogen molecules are combined with hydrogen molecules to make what is called an amino group. All amino acids contain at least one amino group (-NH2) in the alpha position and one carboxyl, and all (except Glycine) contain an asymmetric carbon atom. For this reason, they may exist as isomers.

Amino acids have what is called an R group, which is a side group that distinguishes one amino acid from another.

Most naturally occurring amino acids are of the L-configurations, although D-amino acids are not uncommon in some microorganisms.

The presence of a D-amino acid oxidase in mammalian tissue, however, suggests that the D-forms may play some yet unrecognized role in mammalian protein metabolism.

Amino acids enter into the general metabolic path ways which have been called anabolism and catabolism. 

Every aspects of physiology involves proteins. Individual amino acids serve as neurotransmitters, hormones, and modulator of various physiological processes.

Nine of amino acids are called essential amino acids, because human body cannot make them and must get them though diet. The body can manufacture the remaining 11 amino acids, called nonessential amino acids. 

Consuming the essential amino acids presents no problem to people who regularly eat proteins containing ample amounts of al the essential amino acids such as those of meat, fish, poultry, cheese, eggs, milk and most soybean products.

When amino acid backbones joined end to end, a protein forms. The bonds that from between adjoining amino acids are called peptide bonds. Proteins often contain from 35 to several hundred or more amino acids.
Amino acid: the basic structure of proteins

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Amino acids in beef

Beef is considered by many people to be preferred food in the diet. The protein in beef is complete and high quality.

Evaluation of the amino acid composition of meat protein shows that beef is an excellent source of all of the amino acids required by man.

Beef can supply all the essential amino acids the body needs to build, maintain and repair body tissue and muscle, form hormones and enzymes and increase resistance of infection and disease.

In respect of the essential amino acids, beef would appear to have a somewhat higher content of leucine, lysine and valine than pork or lamb and a lower content of threonine.

The study also shows that amino acids in beef are not destroyed during cooking. Beef protein in amounts as great as 55% of the diet will not raise cholesterol levels in normal men.

The real danger of high protein, high meats diet is that they are frequently accompanied by a high consumption of refined carbohydrates.

Different proteins are composed of varying concentration of different amino acids, so a blend of proteins sources, if chosen wisely, provides an even distribution and concentration of the amino acids necessary for optimal growth.

Amino acids in beef

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Proteins and Amino Acid

Protein was the first substance to be recognized as an essential part of health. Major structural parts of the body’s cells that are made of nitrogen-containing amino acids assembled in chains. About 20% of human body mass is protein.

The word protein was coined by the Dutch chemist Gerardus Mulder in 1838 and comes from the Greek word protos, meaning ‘of first importance’.

Structural components of the cell, antibodies, and many of the hormones are proteins but as much as 90% of cellular proteins are the enzymes upon which fundamental cellular function depends. They may be as many as 1000 different enzymes in a single cell.

The function of a dietary protein is to supply the nitrogen for the synthesis of a a variety of nitrogen-containing compounds such as heme, creatine, hexosamine, dispensable amino acids and to provide those amino acids that cannot be synthesized in adequate amounts.

Proteins catalyze virtually all chemical reactions in the body, regulate gene expression, comprise the major structural elements of all cells, regulate the immune system and form the major constituents of muscle. 

Proteins are considered to be organic matter because they are made up of carbon, oxygen and hydrogen molecules. Proteins are unique that they are also made of up of a nitrogen molecules. The protein molecule is a polymer of amino acids joined in peptide linkages. Although the molecular weight is usually high, there is a vast range in both structure and complexity of protein molecules.

A peptide is a strand of amino acids. A strand of between 4 to 10 amino acids is called an oligopeptide. When a person eats food proteins, whether from cereal, vegetables, beef, fish, or cheese.

The body must first alter them by breaking them down into amino acids; only the can it rearrange them into specific human body proteins.

Hemoglobin for example is one of the proteins with quaternary structure, It consist of four globulin molecules held together by hydrogen bonds. It has a molecular weight of about 64,500; myosin, a muscle protein is estimated to have a molecular weight of about 489,000.
Proteins and Amino Acid

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