Amino acids – fundamental units of protein

Amino acids, peptides and proteins are important constituents of food. They supply the required building blocks for protein biosynthesis.

 The amino acids are the fundamentals units of protein structure. 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.

The term amino acid might mean any molecule containing both an amino group and any type of acid group; however, the term is almost always used to refer to an carboxylic acid. The simplest acid is aminoacetic acid, called glycine.

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.

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.

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 acids – fundamental units of protein

Common properties of protein

Proteins play a fundamental role not only in sustaining life, but also foods derived from plants and animals. Proteins exhibit a number of common properties that just be accounted for in any definition of these compounds:

*There are polymeric of high molecular weight, which are built up by the linking together of a large number of small molecules.

*They are amphoteric, i.e., they being able to act as an acid or a base. This enables them to resist small changes in pH. 

Structure of protein

*Following complete hydrolysis of a protein, the hydrolysate consists entirely of amino acids (except that additional groups, such as heme, iron, copper, may also be found in the case of a conjugate protein). It is commonly recognized that amino acids being linked by peptide bonds formed between α-amino and α-carboxylic acid groups of neighboring amino acids in the polypeptide sequence.

*In their polymeric structures, the amino acid units of proteins are joined together in definite sequences and exist in definite three-dimensional conformations. This sequence built from a limited number of well-defined building blocks, the 20 genetically determined amino acids and a smaller number of posttranslational modifications of them.
Common properties of protein

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

Cysteine

Cysteine is found extensively in the plant foods human ingest. It is found plentifully in the grasses and thus in the meat of domesticated grazing animals.

Cysteine takes its name from cystine, named after the Greek kustis meaning bladder – cystine was first isolated for kidney stones.

Cystine is the stable form of the sulfur rich amino cysteine. The body is capable of converting one of the other as required.

The sulfur in cysteine molecules plays a crucial role in folding proteins into their correct shapes. For examples sulfur independent proteins are keratin – part of hair, skin and nails and collagen – part of connective tissue like cartilage.

Though sulfur itself does not improve nail growth it was found that cystine may have a positive effect on the growth of hypnochium cells.

The amino acid contains a sulfur group that help to function as antioxidant. Cysteine also can be combined with glutamic acid and glycine in liver cells to form glutathione, which is a principle water soluble antioxidant in cells and the blood.

The human body synthesizes the amino acid cysteine for homocysteine and it is part of human hair, skin and nails as the protein keratin.

Cysteine can be found in red pepper, garlic, onions, broccoli, brussel sprouts, oats and wheat germ.

Cysteine

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

Functions of Protein and Individual Amino Acids

Functions of Protein and Individual Amino Acids
Traditionally amino acids have been described as ketogenic and glucogenic, that is, they tend to give rise to acetoacetate or carbohydrate intermediates.

In light of the present knowledge of interrelated metabolic pathways, these terms are obsolete. Nonetheless, it is perhaps useful to remember that phenylalanine, tyrosine, leucine and isoleucine are degraded in part to acetoacetate whereas other amino acids are degraded chiefly to pyruvate, oxaloacetate, alpha-ketoglutarate, succinate and fumarate.

The dietary requirements of certain of the amino acids are influenced by the intake of other nutrients. For example, phenylalanine is converted to tyrosine in the animal cell.

The dietary requirement for phenylalanine, therefore is a function of the total aromatic amino acid content of the diet.

Similarly, methionine may function metabolically as a precursor of other sulfur-containing amino acids so that both of the dietary methionine and cystine determine the requirement for methionine.

The relationship between tryptophan and nicotinic acid is another important example. Tryptophan may be metabolized to form nicotinic acid, and in so doing, contributes to the total amount of the vitamin available for cellular metabolism.

Many of the amino acids are precursors of other significant compounds required in metabolic processes. For example, tyroxine and therefore, phenylalanine give rose to the hormones tyroxine and epinephrine.

Glutamic acid cysteine, and glycine are components of a tripeptide glutathione, which functions in cellular oxidation-reduction reactions.

Sulfur containing amino acids give rise to taurine a bile acid component,. Tryptophan may be metabolized to form serotonin (5-hydroxytryptamine), a tissue hormone that is found predominantly in serum, blood platelets, gastrointestinal mucosa and nerve tissue.

Methionine provides methyl groups for synthesis of choline, creatine and methylation of nicotinamide to its major excretion product N’-methylnicotinamide.

Glycine contributes to the porphyrin ring of hemoglobin and, along with serine, provides part of the structure of the purine and pyrimidines of the nuclei acids.

Two hydroxylated amino acids – hydroxyproline and hydroxylysine – are important constituents of collagen; approximately 12 percent of the total amino acids content of collagen is hydroxyproline.
Functions of Protein and Individual Amino Acids

Proteins and Amino Acid*

Proteins
Nearly half of the dry weight of a typical animal cell is protein. 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 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. Hemoglobin for example, has a molecular weight of about 64,500; myosin, a muscle protein is estimated to have a molecular weight of about 489,000. It is not uncommon for peptide structures of fairly low molecular weight (less than 10,000 and containing less than 100 amino acids) to be designated polypeptides rather than proteins. On the average, about 20 different amino acids occur in most proteins, the amino acids present, their position in the molecule, and the spatial arrangement of the molecule all determine the proteins and characteristics of the proteins. In turn the function of a protein depends, in large measure, on its structure.

Amino acids
The amino acids are the fundamentals units of protein structure. 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. 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.
Proteins and Amino Acid