Which biomolecule is the most versatile

A pure sample of a protein or a polypeptide is essential for the determination of primary structure which involves 3 stages:.

The conformation of polypeptide chain by twisting or folding is referred to as secondary structure. The amino acids are located close to each other in their sequence. It has a rigid arrangement of polypeptide chain. The salient features of a right-handed a-helix which is a stable and more commonly found structure, in the living system Fig.

It is formed between H atom attached to peptide N, and O atom attached to peptide C. All the peptide bonds except the first and last in a polypeptide chain participate in hydrogen bonding. The spacing of each amino acid is 0. The three-dimensional arrangement of protein structure is referred to as tertiary structure. It is a compact structure with hydrophobic side chains held interior while the hydrophilic groups are on the surface of the protein molecule.

This type of arrangement ensures stability of the molecule. Besides the hydrogen bonds, disulfide bonds —S—S , ionic interactions electrostatic bonds and hydrophobic interactions also contribute to the tertiary structure of proteins. The term domain is used to represent the basic units of protein structure tertiary and functions.

A polypeptide with amino acids normally consists of two or more domains. A great majority of the proteins are composed of single polypeptide chains. Some of the proteins, however, consist of two or more polypeptides which may be identical or unrelated. Such proteins are termed as oligomers and possess quaternary structure.

The individual polypeptide chains are known as monomers, protomers or subunits. A dimer consist of two polypeptides while a tetramer has four. The monomeric subunits are held together by non-covalent bonds namely hydrogen bonds, hydrophobic interactions and ionic bonds.

Proteins are classified in several ways. Three major types of classifying proteins based on their function, chemical nature and solubility properties and nutritional importance are discussed here. Based on the function they perform, proteins are classified into different groups with examples.

This is a more comprehensive and popular classification of proteins. It is based on the amino acid composition, structure, shape and solubility properties. Proteins are broadly classified into 3 major groups Table Besides the amino acids, these proteins contain a non-protein moiety known as prosthetic group or conjugating group.

These are the denatured or degraded products of simple and conjugated proteins. The above three classes are further sub-divided into different groups. The summary of protein classification is given in the Table Among the simple proteins, globular proteins are spherical in shape, soluble in water or other solvents and digestable e.

Scleroproteins fibrous proteins are fiber like in shape, insoluble in water and resistant to digestion e. The conjugated proteins may contain prosthetic groups such as nucleic acid, carbohydrate, lipid, metal etc. The primary derived proteins are produced by agents such as heat, acids, alkalies etc. Isoprenoids and pigments are organic compounds mostly distributed in plant kingdom. They perform a wide variety of functions.

Isoprenoids are also called as terpenoids or terpenes as they are found in turpentine oil in high concentrations. The naturally occurring isoprenoids are composed of a five carbon isoprene unit. A majority of the isoprenoids are formed by joining of isoprene units head to tail as depicted below. Classification of terpenes :. The classification of terpenes is mainly based on the number of isoprene C 5 H 8 units present. The major classes of terpenes with selected examples are given in Table Pigments are cloured organic compounds found in the living organisms, mostly in plants, and to a minor extent in animals.

Chemically, pigments are high molecular weight molecules, mostly composed of unsaturated hydrocarbons. Some of the pigments also contain cyclic structures. The most abundant coloured compound in the world is chlorophyll, the photosynthetic pigment. There are different types of chlorophylls c, d, e, a with slight variation in colours — green, greenish blue, greenish yellow.

Structurally, chlorophylls are composed of tetrapyrroles pyrrole rings with their nitrogen linked to magnesium. Tetrapyrroles are also found in heme in certain proteins. These include hemoglobin, cytochromes, catalase and peroxidase. The colour of carotenoids is variable, generally yellow, orange or red. A large number of carotenoids about have been identified in plant kingdom e. Anthocyanins are a group of flavonoids which represent the natural phenolic products. Anthocyanins are coloured compounds, mostly found in flowers and fruits.

They contain a common ring structure called anthocyanidin. Being present in trace amounts, quinoid pigments do not significantly contribute to visible colours. They however, perform some other functions e. The most common quinoid pigments are benzoquinones, naphthoquinones, anthraquinones, tannins and lignins.

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Performance Performance. In sickle-cell anemia, a hereditary human disorder, the hemoglobin molecule is defective. In people with sickle-cell anemia, a valine residue occurs at position 6. Because all biological macromolecules are made from the same three dozen subunits, it seems likely that all living organisms descended from a single primordial cell line.

These subunits are proposed to have had, singly and collectively, the most successful combination of chemical and physical properties for their function as the raw materials of biological macromolecules and for carrying out the basic energy-transforming and self replicating features of a living cell.

These primordial organic compounds may have been retained during biological evolution over billions of years because of their unique fitness. We come now to a puzzle. Apart from their occurrence in living organisms, organic compounds, including the basic biomolecules, occur only in trace amounts in the earth's crust, the sea, and the atmosphere.

How did the first living organisms acquire their characteristic organic building blocks? In , the biochemist Aleksandr I. Oparin proposed a theory for the origin of life early in the history of the earth, postulating that the atmosphere was once very different from that of today.

Rich in methane, ammonia, and water, and essentially devoid of oxygen, it was a reducing atmosphere, in contrast to the oxidizing environment of our era. In Oparin's theory, electrical energy of lightning discharges or heat energy from volcanoes Fig.

These compounds then dissolved in the ancient seas, which over many millenia became enriched with a large variety of simple organic compounds. In this warm solution the "primordial soup" some organic molecules had a greater tendency than others to associate into larger complexes.

Over millions of years, these in turn assembled spontaneously to form membranes and catalysts enzymes , which came together to become precursors of the first primitive cells. For many years, Oparin's views remained speculative and appeared untestable. Figure Lightning evoked by a volcanic eruption that resulted in the formation of the island of Surtsey off the coast of Iceland in The intense fields of electrical, thermal, and shock-wave energy generated by such cataclysms, which were frequent on the primitive earth, could have been a major factor in the origin of organic compounds.

Several developments have allowed more refined studies of the type pioneered by Miller and Urey, and have yielded strong evidence that a wide variety of biomolecules, including proteins and nucleic acids, could have been produced spontaneously from simple starting materials probably present on the earth at the time life arose. Figure Spark-discharge apparatus of the type used by Miller and Urey in experiments demonstrating abiotic formation of organic compounds under primitive atmospheric conditions.

After subjecting the gaseous contents of the system to electrical sparks, products were collected by condensation. Biomolecules such as amino acids were among the products see Table Modern extensions of the Miller experiments have employed "atmospheres" that include C0 2 and HCN, and much improved technology for identifying small quantities of products. The formation of hundreds of organic compounds has been demonstrated Table These compounds include more than ten of the common amino acids, a variety of mono-, di-, and tricarboxylic acids, fatty acids, adenine, and formaldehyde.

Under certain conditions, formaldehyde polymerizes to form sugars containing three, four, five, and six carbons. The sources of energy that are effective in bringing about the formation of these compounds include heat, visible and ultraviolet UV light, x rays, gamma radiation, ultrasound and shock waves, and alpha and beta particles.

In addition to the many monomers that form in these experiments, polymers of nucleotides nucleic acids and of amino acids proteins also form. Some of the products of the self condensation of HCN are effective promoters of such polymerization reactions Fig. F igure Among the products of electrical discharge through an atmosphere containing HCN are compounds such as those in a.

These compounds promote the polymerization of monomers such as amino acids into polymers b. In modern organisms, nucleic acids encode the genetic information that specifies the structure of enzymes, and enzymes have the ability to catalyze the replication and repair of nucleic acids.

The mutual dependence of these two classes of biomolecules poses the perplexing question: which came first, DNA or protein? The division of function between DNA genetic information storage and protein catalysis was, according to the "RNA world" hypothesis, a later development Fig. New variants of self replicating RNA molecules developed, with the additional ability to catalyze the condensation of amino acids into peptides.

Occasionally, the peptide s thus formed would reinforce the self replicating ability of the RNA, and the pair-RNA molecule and helping peptide-could undergo further modifications in sequence, generating even more efficient self replicating systems. Sometime after the evolution of this primitive protein-synthesizing system, there was a further development: DNA molecules with sequences complementary to the self replicating RNA molecules took over the function of conserving the "genetic" information, and RNA molecules evolved to play roles in protein synthesis.

Proteins proved to be versatile catalysts, and over time, assumed that function. Lipidlike compounds in the primordial soup formed relatively impermeable layers surrounding self replicating collections of molecules. The concentration of proteins and nucleic acids within these lipid enclosures favored the molecular interactions required in self replication. This "RNA world" hypothesis is plausible but by no means universally accepted.

The hypothesis does make testable predictions, and to the extent that experimental tests are possible within finite times less than or equal to the life span of a scientist! The earth was formed about 4. An international group of scientists showed in that certain ancient rock formations stromatolites; Fig. Somewhere on earth during that first billion-year period, there arose the first simple orga.

Figure Ancient reefs in Australia contain fossil evidence of microbial life in the sea of 3. Bits of sand and limestone became trapped in the sticky extracellular coats of cyanobacteria, gradually building up these stromatolites found in Hamelin Bay, Western Australia a. Article Views Altmetric -. Citations 7. Supporting Information. Cited By. This article is cited by 7 publications. Friedrich, Tza-Huei Wang.

Analytical Chemistry , 92 8 , Extension of hydrodynamic chromatography to DNA fragment sizing and quantitation. Heliyon , 7 9 , e Diffraction-based label-free photothermal detector for separation analyses in a nanocapillary. Journal of Chromatography A , , Fluorescence coupled capillary electrophoresis as a strategy for tetrahedron DNA analysis.

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