Molecular Basis of Inheritance
DNA and RNA
• Nucleic acids are long polymers of nucleotides and are of two types: DNA and RNA.
• 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.
• DNA is made up of deoxyribose sugar, two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between complimentary bases adenine, thymine, cytosine and guanine.
• Watson and Crick proposed the double helix model for the structure of DNA. According to Chargaff’s rule, the molar ratio between the base pairs is always equal in DNA.
• Frederick griffith discovered the transforming principle in a series of experiments with Streptococcus pneumoniae.
• In the remote past, ‘RNA world’ existed where RNA used to be the multitasker, genetic material and biological catalyst.
• The flow of information from DNA to proteins via RNA is known as central dogma and the backflow of information from RNA to DNA is known as reverse transcription.
DNA replication and transcription
• The DNA replicates in order to carry genetic information from one generation to another. It can replicate in three ways; dispersive, conservative and semi- conservative.
• In 1958, Matthew Stanley Messelson and Franklin William Stahl experimented on DNA replication on E. coli cells and detected that DNA replication is semi-conservative.
• DNA polymerase is an important enzyme required in DNA replicationthat synthesises DNA at a very fast speed.
• The point of origin of replication in DNA is called origin of replication, where the DNA replication begins in E.coli.
• Two daughter strands are formed after each cycle of replication and each daughter DNA duplex is a practically hybrid molecule with one parental strand and one new strand.
• The process of copying hereditary information from DNA to RNA is called transcription.
• Transcription is completed in three steps, namely, initiation, elongation and termination.
Genetic code and translation
• Genetic code is a three lettered representation of different bases namely Adenine, Guanine, Thymine and Cytosine.There are 61 codons and three stop codons.
• Mutation is the heritable change in DNA, which is passed on through generations.
• Transfer RNA is a compound structure forming several loops and arms due to complementary base-pairing. Translation is a cellular process in which nucleotide sequence of mRNA transcript is translated into amino acid sequence in a polypeptide.
• Initiation, elongation and termination are the three major steps of translation.
• The regulation of gene expression can occur at transcriptional or translational level.It can either be positive or negative.
• The regulation of gene expression in bacteria is affected through operons such as Lac operon and tryptophan operon.
Human genome project and DNA fingerprinting
• Human genome project was a mega project that aimed to sequence the entire human genome.
• DNA Fingerprinting is a technique used to findout variations in individuals of a population at DNA leveland it is based on the principle of polymorphism in DNA sequences.