Molecular Basis of Inheritance

Nucleic acids are long polymers of nucleotides. The nucleic acids are of two types: DNA and RNA. DNA is a polymer of nucleotide and is made up of pentose sugar, nitrogenous base and phosphoric acid. There are two types of nitrogenous bases – Purines (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine). The double stranded helical structure of DNA is formed by the hydrogen bonding between the bases from opposite strands. In RNA the uracil is found at the place of thymine (5-methyl uracil, another chemical name for thymine). In prokaryotes DNA is present in the form of nucleoid. In eukaryotes the DNA is packed in the form nucleosomes. In 1928, Frederick Griffith gave the transforming principle and concluded there is transfer of genetic material. In 1952 Alfred Hershey and Martha Chase proved the DNA is the genetic material. The DNA replicates semi conservatively. The flow of information from DNA to protein via RNA is called central dogma and was proposed by Francis Crick in 1958. During transcription one strand of DNA is transcribed into RNA. In eukaryotes, the gene consists of coding sequence called exon and non-coding sequence called intron. The Introns are removed and exons are joined to produce functional RNA by the process of splicing. The genetic code is the nucleotide sequence that determines specific amino acid sequence for the protein synthesis. There are 61 codons and three stop codons. Translation is a cellular process, which occurs in cytoplasm and in this process; nucleotide sequence of mRNA transcript is translated into amino acid sequence in a polypeptide. The regulation of gene expression can occur at transcriptional or translational level and it can either be positive (triggers transcription of genes) or negative (stops transcription of genes). The regulation of gene expression in bacteria is affected through operons which are made up of a group of genes. Examples of operon are Lac operon and tryptophan operon. Human genome project was a mega project that aimed to sequence every base in human genome.DNA Fingerprinting is a technique to find out variations in individuals of a population at DNA level. It is based on the principle of polymorphism in DNA sequences.

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