BIOCHEMISTRY: Chemistry Of Nucleic Acid by Saqib nayyar.

Nucleic Acids:

A 22-years old swiss phyician and chemist, Friedrich Miescher isolated substance from the nuclei of pus cells, which was quite different from other molecules and named it as 'nuclein' . Later , it was found that the nuclein had acidic properties and hence it was renamed as nucleic acid .

Nucleic acids are present in all organism , from virus to man .

The macromolecules are present either in the free-state or boun

d to proteins a nucleoproteins .Like proteins, the nucleic acids are biopolymer of high molecular weight with mononucleotide as their sub-units ( monomers ). The nucleic acids are the long chain of polynucleotide in which mononucleotides are linked with each other.

There are two kinds of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) . DNA is found mainly in the chromatin of the cell nucleus, whereas most of the RNA (90%) is present in the cell cytoplasm and a little (10%) in the nucleolus.

Nucleotide is a molecule which consists of following three parts.

1) Pentose sugar (5 carbon).
2) Phosphoric acid ( H3 PO4).
3) A nitrogenous base.

Pentose sugar found in nucleotide is either Ribose (C5 H 10 O5) or Deoxyribose (C5 H10 O4) .

Ribose is found in RNA nucleotides which Deoxyribosome sugar is found in DNA nucleotides, both of them are distinguished primarily on the basis of this pentose sugar.
This sugar behave as basic skeleton.

Phosphoric acid is common in all nucleotides. It is attached with 5th carbon of pentose sugar in each nucleotide

There are two basic types of nitrogenous bases I.e. Purine and
pyrrimidin. Purine includes two nitrogenous bases named Adenine (A) and Guanine (G) pyrimidine includes three nitrogenous bases cytosine (C), thymine (T) and uracil (U) . The nucleotides differ on the basis of their nitrogenous bases.

Formation of nucleotide takes place in two steps. At first step the nitrogenous base combines with pentose sugar at its first carbon to form a nucleoside . At the second step the phosphoric acid combines with the 5th carbon of pentose sugar to form a nucleotide.

1 . Mononucliotide:

Generally,nucleotides are found in the nucleic acid as polynucleotide but they also found as mononucleotide and dinucleotide. Mononucleotides exist singly in the cell or as a part of other molecules. These are not the part of DNA or RNA . Some of these have extra phosphate groups e.g ATP (Adenosine triphosphate).

An unstable molecule and carries energy from place to place within a cell. It is synthesized from ADP (Adenosine diphosphate) and inorganic phosphate by capturing energy during photosynthesis.

Energy is utilized to derive energy demanding reactions such as in synthesis of proteins, lipids, carbohydrates, mechanical energy for cyclosis, contractility , cell-division , movement of flagella, active transport etc.

ATP consists of Adenosine ( Adenosine and ribose sugar ) and three phosphate ; among them two are energy rich phosphate bond.
During conversion of ATP into ADP , the free energy releases which is considerable large i.e. 31.81Kj or 7.3K. Cal / mole energy.

2 . Dinucleotide :

Sometimes two nucleotides are covalently bounded together, to form compounds are called dinucleotide . One of the well-known dinucleotide is Nicotinamide adenine dinucleotide ( NAD ).

Nicotineamide is a vitamin constituent.

NAD is a co-enzyme ( co-enzymes are the organic molecules ( non protein ) which bind to enzyme ( protein ) and serve as a carries for chemical groups or electrons ) that carries electron and work with dehydrogenase enzyme. It removes two hydrogen atom ( e- + 2H+ ) from its substrate, both electrons, but only one hydrogen ion is passed to NAD which reduces it to NADH.

3 . Polynucleotide ( Nucleic acids as informational macromolecules ) :

Nucleic acids are the polynucleotides . They have a variety of role

in living organisms. They make it possible for cells to function according to specific patterns and give rise to new cells that either function similarly or develop new function, according to plans encoded in encoded in the nucleic acid .

LIFE FATE MATERIAL

DNA

Genetic information is encoded in a nucleic acid molecule. Four different nucleotides make up each informational nucleic acid molecules . The cell interpretes the information present many nucleic acid molecules as sequence of amino acid in protein and peptide molecules. The synthesis of proteins with definite sequences of amino acid as controlled amounts of protein is observed as the expression of heredity of an organism which generally give the physical appearance of that particular characters.

DNA as hereditary material:

Transformation of the one type of bacteria in to another type and infection of bacteria by bacteriophage provides first evidence that DNA is the hereditary material. Griffith discovered that living bacteria can acquire genetics material from dead bacteria and transform live bacteria from non-virulent to virulent . Avery and his colleagues showed that the genes taken up living bacteria during transformation were composed of DNA.

DNA AS A HEREDITY MATERIAL

A bacteriophage consists solely of DNA & protein. When it infects a bacterium, the phage injects its DNA only into the bacterium, where it directs the synthesis of more phages Hershey and Chase thus experimentally confirmed that DNA must be the genetic material. DNA has specific sequences of nitrogenous bases . These sequences of bases in DNA can which encode vast amount of information. Since the nitrogenous bases are of four type, it is amazing that how just four different types of bases in DNA encode all of the information needed to 20 amino acids. Each sequence represents a unique set of genetic institutions encode a huge amount of information in the form of genetic codes.

RNA as a carries of information :

In Eukaryotic cells DNA is located in the nucleus while most of the synthesis and metabolic functions occur in the cytoplasm under the instruction of DNA. Therefore, DNA requires some intermediate molecules that carry informations from DNA to the cytoplasm. These molecules are ribonucleic acids or RNA 's .

Genetic information in cell from DNA to RNA than to cytoplasm in a two step process for the synthesis of proteins.