Human genome encodes the genetic information in DNA. Human contains the DNA in 23 chromosomes pair in the cell nuclei and also contains small DNA within mitochondria. The total length of the human genome is over 3 billion base pair. The genome is organized in 22 paired chromosomes and one pair contain X chromosome (male contain one X chromosomes while female contains two X chromosomes) and Y chromosomes (only male contains the one Y chromosome). Human genomes also includes both protein coding and non-coding in the genome. Here we will briefly discuss about DNA, RNA, coding and non-coding RNA and their significance.
DNA (deoxyribonucleic acid): DNA is a molecule that encodes the genetic information. It functions in all known living organisms and many viruses. DNA is first identified and isolated by Friedrich Miescher but double helix of DNA was discovered by James Watson and Francis Crick in 1953 and showed how nucleotides are organized within DNA.
Each nucleotide in DNA has three components:
' A sugar molecule
' A phosphate molecule, which has acidic chemical properties
' A nitrogen molecule, which has slightly basic chemical properties.
The chemical interactions are formed between the phosphates of one nucleotide to the sugar of another nucleotide. The nitrogen containing bases are not involved in these interactions. The chains in the double helix are held together by weal hydrogen bonds between particular pair of bases. In the base pairing A (adenine) interacts with T (thymine) while G (guanine) interacts with C (cytosine) in the base pairing. DNA is long polymer of repeating units which is very small. The backbone of the DNA strand is made from alternating phosphate and sugar residue. The sugar in the DNA is deoxyribose at 2' in the pentose ring. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atom of adjacent sugar ring. In a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand and strands are called antiparallel. The asymmetric ends of the DNA strands are called the 5' which have phosphate group and 3' ends which have hydroxyl group. Uracil group is not usually not found in DNA. DNA have two grooves in the backbone, one is major groove which is 22A?? wide and other is minor groove which is 12 A?? wide. In the base pairing AT forming two hydrogen bonds which GC forming three hydrogen bonds, so high GC content DNA is more stable than low GC content DNA. The stability of DNA also depends on the Tm (melting temperature at which ds molecules are converted to ss molecules) which is dependent on the ionic strength and concentration of DNA. A DNA sequence is called sense if its sequence is the same as that of a messenger RNA copy is translated into protein and if the sequence on the opposite strand is called the antisense sequence. Both sense and antisense sequences can exist on different parts of the same of the strand of the DNA. DNA exists in many conformations like A-DNA, B-DNA, Z-DNA forms but B-DNA form is most common form found in the cells. The conformation that DNA adopts depends on the hydration level, DNA sequence, the amount and direction of supercoiling, chemical modification of bases, the type and concentration of metal ions, as well as presence of polyamines in the solution.
DNA can be damaged by many sorts of mutagens, which change the DNA sequence. Mutagens include oxidizing agents, alkylating agents and also high energy electromagnetic agents.
DNA in technology:
Genetic engineering: In this technology genetically modified organism used to produce product which have importance in medical research or in agriculture.
Forensics: This use DNA in blood, semen, skin, saliva or hair found at a crime scene to identify a matching DNA of an individual. The lengths of variable sections of repetitive DNA such as short tandem repeats and minisatellites are compared between people.
Bioinformatics: It involves the searching, data mining of biological data, manipulation of data and DNA sequence data. The development of techniques to store and search DNA sequences have led to widely applied in computer science, searching algorithms, machine learning and database theory.
Nanotechnology: It uses the unique molecular recognition properties of DNA and other nucleic acids to create self - assembling branched DNA complexes with useful properties.
History and anthropology: Inherited DNA collects mutations over time which contains historical information and by comparing DNA sequences, geneticists can infer the evolutionary history of organisms by phylogeny. This field of phylogenetic is a powerful tool in evolutionary biology. In anthropology, ecological genetics are studies.
Information storage: DNA is able to code information as a digital data storage by a mechanism.
RNA (ribonucleic acid): RNA is a large biological molecules that perform multiple roles in the decoding, coding and expression of genes. RNA is assembled as a chain of nucleotides and it is usually single stranded. The chemical structure of RNA differ in three ways:
' RNA is a single-stranded molecule and has a much shorter chain of nucleotides.
' RNA contains ribose (attachment of 'OH in 2' position of pentose ring) which make it less stable because it is more prone to hydrolysis.
' RNA contains uracil (U), which is an unmethylated form of thymine.
Most biologically active RNAs including mRNA, tRNA, rRNA, snRNA and other non-coding RNAs which contain self-complementary sequences that allow parts of the RNA to fold. RNA can achieve chemical analysis like enzymes.
Usually RNA is synthesized by an enzyme 'RNA polymerase' which binds to a promoter sequence by transcription process.
Messenger RNA (mRNA) carries information about a protein form DNA to the ribosomes (the site of protein synthesis in the cell). It is coded so that every three nucleotides correspond to one amino acid. Each codon encodes for a specific amino acids, expect the stop codons, which terminate protein synthesis. mRNA is currently being investigated for its potential use in the treatment and prevention of disease. mRNA based vaccines are being developed as cancer immunotherapy and prophylactic vaccines for infectious diseases.
Transfer RNA (tRNA) is a small RNA chain that transfer a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation.
Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. The ribosome binds mRNA and carries out protein synthesis. The ribosomal RNAs form two subunits; the large subunit (LSU) and small subunit (SSU). Ribosomal RNA characteristics are important in medicine and in the evolution.
A non-coding RNA (ncRNA) is a functional RNA molecule that is not translated in to protein. Non-coding RNA genes include highly abundant and functionally important RNAs such as tRNA, rRNA, snoRNAs, microRNAs, siRNAs, snRNAs, exRNAs and piRNAs. Mutation or imbalances in the non-coding RNA can cause several diseases which are; Cancer, Autism, Alzheimer's disease, Prader-Willi syndrome etc.
MicroRNA: It is a small non-coding RNA molecule which is found in animals, plants and some viruses. It function is transcriptional and post transcriptional regulation of gene expression. microRNA were discovered in 1993 by Victor Ambros, Rosalind Lee and Rhonda Feinbaum during the study of the gene lin-14 in C.elegans development. microRNA are produced from either their own genes or from introns. In some cases microRNA gene is transcribed together with its host genes; this provides a means for coupled regulation of miRNA and protein-coding gene. microRNA genes are usually transcribed by RNA polymerase II. RNA polymerase III transcribes some miRNAs, especially those with upstream Alu sequences, transfer RNAs, and mammalian wide interspersed repeat promoter units. . It's play major role in inherited diseases, cancer, heart disease, nerve disease but in viral disease, parasitic disease it also play role to generate to disease.
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