Structural proteins that bind DNA are well-understood examples of non-specific DNA-protein interactions. Within chromosomes, DNA is held in complexes with structural proteins. These proteins organize the DNA into a compact structure called chromatin. In eukaryotes this structure involves DNA binding to a complex of small basic proteins called histones, while in prokaryotes multiple types of proteins are involved.The histones form a disk-shaped complex called a nucleosome, which contains two complete turns of double-stranded DNA wrapped around its surface. These non-specific interactions are formed through basic residues in the histones making ionic bonds to the acidic sugar-phosphate backbone of the DNA, and are therefore largely independent of the base sequence. Chemical modifications of these basic amino acid residues include methylation, phosphorylation and acetylation.These chemical changes alter the strength of the interaction between the DNA and the histones, making the DNA more or less accessible to transcription factors and changing the rate of transcription.Other non-specific DNA-binding proteins in chromatin include the high-mobility group proteins, which bind to bent or distorted DNA.These proteins are important in bending arrays of nucleosomes and arranging them into the larger structures that make up chromosomes

A distinct group of DNA-binding proteins are the DNA-binding proteins that specifically bind single-stranded DNA. In humans, replication Protein A is the best-understood member of this family and is used in processes where the double helix is separated, including DNA replication, recombination and DNA repair. binding proteins seem to stabilize single-stranded DNA and protect it from forming stem loops or being degraded by nucleases

GENE THERAPHY

Each gene has a special job to do. It carries blueprints(said to be instructions).
Each of our biological parents has two copies of each of their genes, and each parent passes along just one copy to make up the genes we have. Genes that are passed on to us determine many of our traits, such as our hair color and skin color and many other characteristics. Nowadays scientists are very busy studying genes.
Gene therapy uses the technology of genetic engineering to cure or treat a disease caused by a gene that has changed in some way. This is a new kind of medicine, and scientists are still doing experiments to see if it works. One method they are trying is replacing sick genes with healthy ones.Gene therapy is the insertion of genes into an individual's cells and tissues to treat diseases, such as hereditary diseases.Although the technology is still in its infancy, it has been used with some success. Scientific breakthroughs continue to move gene therapy toward mainstream medicine.The biology of human gene therapy remains complex and many techniques need further development.Gene therapy is nowadays the basis to many entertainment programs and popular video games.

PROPERTIES OF DNA

DNA is a long polymer made from repeating units called nucleotides.In living organisms, DNA does not usually exist as a single molecule, but instead as a pair of molecules that are held tightly together.The backbone of the DNA strand is made from alternating phosphate and sugar residues.A DNA sequence is called "sense" if its sequence is the same as that of a messenger RNA copy that is translated into protein.
DNA can be twisted like a rope in a process called DNA supercoiling.DNA exists in many possible conformations that include A-DNA, B-DNA, and Z-DNA forms, although, only B-DNA and Z-DNA have been directly observed in functional organisms.
DNA usually occurs as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell makes up its genome; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes.
The genetic information in a genome is held within genes, and the complete set of this information in an organism is called its genotype.

GENETIC ENGINEERING

Genetic engineering ia a term that apply to the direct manipulation of an organism's genes. Genetic engineering uses the techniques of molecular cloning and transformation to alter the structure and characteristics.Genetic engineering techniques have been applied to various industries,medicine and agriculture.
Human genetic engineering is the modification of an individual's genotype with the aim of choosing the phenotype of a newborn or changing the existing phenotype of a child or adult.Genetic engineering is a laboratory technique used by scientists to change the DNA of living organisms. Genetic engineering is defined as a set of technologies that are used to change the genetic makeup of cells and move the genes from one species to another to produce new organisms. Genetic Enginering holds many promises for the future. It brings with it possibilities of longer, healthier lives.
With genetic engineering, we would have the ability to clone a loved one or a favorite pet, ending the pain of loss that comes from death. It would also give us the ability to grow replacement organs, limbs, skin, or virtually any other body part.

BIOLOGICAL FUNCTIONS

DNA usually occurs as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell makes up its genome; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes.[64] The information carried by DNA is held in the sequence of pieces of DNA called genes. Transmission of genetic information in genes is achieved via complementary base pairing. For example, in transcription, when a cell uses the information in a gene, the DNA sequence is copied into a complementary RNA sequence through the attraction between the DNA and the correct RNA nucleotides. Usually, this RNA copy is then used to make a matching protein sequence in a process called translation which depends on the same interaction between RNA nucleotides. Alternatively, a cell may simply copy its genetic information in a process called DNA replication. The details of these functions are covered in other articles; here we focus on the interactions between DNA and other molecules that mediate the function of the genome.

DNA PROFILING

DNA profiling (also called DNA testing, DNA typing, or genetic fingerprinting) is a technique employed by forensic scientists to assist in the identification of individuals on the basis of their respective DNA profiles. DNA profiles are encrypted sets of numbers that reflect a person's DNA makeup, which can also be used as the person's identifier. The process begins with a sample of an individual's DNA Which is also called as Reference sample.
A reference sample is then analyzed to create the individual's DNA profile using one of a number of techniques, discussed below. The DNA profile is then compared against another sample to determine whether there is a genetic match.
The chemical structure of everyone's DNA is the same. The only difference between people (or any animal) is the order of the base pairs.DNA fingerprinting is a way of identifying a specific individual, rather than simply identifying a species or some particular trait. It is also known as genetic fingerprinting or DNA profiling.
The vast majority of a human's DNA will match exactly that of any other human, making distinguishing between two people rather difficult. DNA fingerprinting uses a specific type of DNA sequence, known as a microsatellite.

TRANSCRIPTION AND TRANSLATION

A gene is a sequence of DNA that contains genetic information and can influence the phenotype of an organism. Within a gene, the sequence of bases along a DNA strand defines a messenger RNA sequence, which then defines one or more protein sequences. The relationship between the nucleotide sequences of genes and the amino-acid sequences of proteins is determined by the rules of translation, known collectively as the genetic code. The genetic code consists of three-letter 'words' called codons formed from a sequence of three nucleotides (e.g. ACT, CAG, TTT).

In transcription, the codons of a gene are copied into messenger RNA by RNA polymerase. This RNA copy is then decoded by a ribosome that reads the RNA sequence by base-pairing the messenger RNA to transfer RNA, which carries amino acids. Since there are 4 bases in 3-letter combinations, there are 64 possible codons (43 combinations). These encode the twenty standard amino acids, giving most amino acids more than one possible codon. There are also three 'stop' or 'nonsense' codons signifying the end of the coding region; these are the TAA, TGA and TAG codons.