Diseases are caused by pathogenic organisms such as viruses, bacteria, or fungus.     Normally harmless but under certain conditions, they can be fatal and can cause death too. They can be spread from one person to another directly or indirectly. Infectious diseases are caused by infection-causing organisms that use the human body for surviving, reproducing and colonizing.

Temperature affects the nucleic acid structure of double-stranded DNA (dsDNA). The melting temperature is defined as the temperature at which half of the DNA strands are in the random coil or single-stranded (ssDNA) state. Tm depends on the length of the DNA molecule and its specific nucleotide sequence. DNA, when in a state where its two strands are dissociated.

Recombinant DNA technology is the joining together of DNA molecules from two different species. The recombined DNA molecule is inserted into a host organism to produce new genetic combinations that are of value to science, medicine, agriculture, and industry.  A geneticist is to isolate, characterize, and manipulate genes. Recombinant DNA technology is based primarily on two other technologies, cloning and DNA sequencing. Cloning is undertaken in order to obtain the clone of one particular gene or DNA sequence of interest. Next step after cloning is to find and isolate that clone among other members of the library (a large collection of clones). a segment of DNA has been cloned, its nucleotide sequence can be determined.

RNA processing requires proper splicing of a primary transcript and modification of the 5′- and 3′-ends to generate a mature mRNA and the focus will be on the interdependence of these RNA-processing events with ongoing transcription.

DNA is repaired by removal of the damaged bases followed by resynthesized of the excised region. Some lesions in DNA can be repaired by direct reversal of the damage, which may be a more efficient way of dealing with specific types of DNA damage that occur frequently.

Nucleic acids are long linear or circular macromolecules, either DNA or various types of RNA that composed of linked nucleotides. These molecules carry genetic information that directs all cellular functions.

·Messenger RNA (mRNA)

·Transfer RNA (tRNA)

·Ribosomal RNA (rRNA)

Nucleic acids are the main information-carrying molecules of the cell, and, by directing the process of protein synthesis, they determine the inherited characteristics of every living thing.

Nucleic acid probes are used not only to detect mRNA, but to assess interphase chromosomes in tumor cells. Probe is placed into contact with the sample under conditions that allow the probe sequence to hybridize with its complementary sequence. Probes may consist of either DNA or RNA, and they vary in length from short oligonucleotides to mutagenic chromosomal segments cloned into bacteria.

Nucleic acids are polynucleotides that are long chainlike molecules composed of a series of nearly identical building blocks called nucleotides. Each nucleotide consists of a nitrogen-containing aromatic base attached to a pentose (five-carbon) sugar, which is in turn attached to a phosphate group.

 PNA are synthetic analog of DNA with a repeating N-(2-aminoethyl)-glycine peptide backbone connected to purine and pyrimidine nucleobases via a linker. The unique properties of PNA, including resistance to enzymatic digestion, higher bio stability combined with great hybridization affinity toward DNA and RNA, it has attracted great attention toward PNA- based technology as a promising approach for gene alteration. However, an important challenge in utilizing PNA is poor intracellular uptake. Some strategies have been developed to enhance the delivery of PNA in order to reach cognate site.

Protein biosynthesis subject is defects in mitochondrial oxidative phosphorylation, deficiency in mitochondrial translation. protein synthesis in the mitochondria, mitochondrial encephalomyopathy with lactic acid and stroke-like episodes, protein synthesis directed by the nucleus, the ribosome, structure of transfer RNA (tRNA), initiation and amino acid tRNA synthase, elongation and peptidyltransferase ribozyme, termination, inhibitors of protein synthesis, proteins synthesized in the cytoplasm but destined for mitochondria, proteins destined for the nucleus, and proteins destined for other sites including the plasma membrane and secretion from the cell.

The two ribbons symbolize the two phosphate-sugar chains, and the horizontal rods the pairs of bases holding the chains together. The vertical line marks the fiber axis. The two strands of the helix run in opposite directions, meaning that the 5′ end of one strand is paired up with the 3′ end of its matching strand.

The primary nucleic acid bases are adenine, cytosine, guanine, thymine, and uracil. A base pair usually involves hydrogen bonding between a purine and a pyrimidine In DNA guanine base pairs with cytosine while adenine base pairs with thymine.

The discovery of natural RNA catalysts has prompted chemical biologists to pursue artificial nucleic acids that have catalytic activities. Such artificial nucleic acid enzymes may comprise either RNA or DNA. The term ‘nucleic acid enzyme’ is used to identify nucleic acids that have catalytic activity. Ribozymes are found in nature and mediate phosphodiester bond cleavage and formation and peptide bond formation.

Novel sequencing methodology which should be readily and completely automated. The method relies on fragmentation of a nucleotide or deoxynucleotide sequence into short fragments, and subsequent quantitation of the fragments by hybridization to olio Deoxynucleotides on a solid support

Molecular Biology is the field of biology that studies the composition, structure and interactions of cellular molecules such as nucleic acids and proteins that carry out the biological processes essential for the cell's functions and maintenance. It includes wide-ranging coverage of problems related to molecular and cell biology: