• DNA was, for the first time, isolated from nuclei of pus cells by Johann Friedrich Miescher in 1869.
• The phenomenon of transfer of genetic material from one cell to another that alter the genetic make-up of the recipient cell is called transformation and this was discovered by Frederick Griffith in 1928.
• The experiments conducted by Oswald Avery, Colin Macleod and Maclyn McCarty revealed DNA as the likely transforming agent.
• The experiments conducted by Hershey and Chase in 1952 provided strong evidence that DNA is the genetic material.
• Gene is the unit of inheritance that controls a specific trait or character and may also be expressed in alternative forms known as alleles.
• The expression of DNA through the synthesis of polypeptide chain via RNA synthesis represents the Central Dogma of genetics.
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• The fact that one gene encodes one polypeptide, the central dogma also got modified from one gene, one protein to one gene, one polypeptide.
• Each gene must satisfy the test to be a unit of function, unit of recombination and unit of mutation.
• The kind of DNA replication in which the parental duplex DNA form two identical daughter duplex, each of which consists of one parental stand and one newly synthesised daughter strand is called semi-conservative replication.
• It was Messelson and Stahl who experimentally distinguished between the old and new stand of the DNA after replication using two isotopes of Nitrogen, 14N and 15N in their experiment.
• Several enzymes and proteins are involved in the replication of DNA in both prokaryotes and eukaryotes such as DNA polymerase, primase, helicase, single-strand binding protein, topoisomerase, DNA ligase, DNA-dependent RNA polymerase.
• Replication usually starts at a specific site on a DNA sequence known as origin of replication.
• The new strand that is synthesised continuously in 5'→3' direction is called the leading strand.
• The DNA strands synthesised discontinuously with the Okazaki fragments are called the lagging strand
• Transcription is a process by which genetic information is transferred from DNA to mRNA.
• Translation is the process by which information is transferred from mRNA to polypeptide chain and consists of four stages such as (i) charging of tRNA (ii) initiation (iii) elongation, and (iv) termination.
• In case of reverse transcription the information present in the genetic material which is RNA is first transferred to a single stranded complementary DNA strand and is then converted into a double stranded DNA.
• Within a gene, only one of the nucleotide strands is normally transcribed into RNA. The DNA strand whose nucleotide sequence is complementary to that of the mRNA is called the template or antisense strand, while the other strand whose base sequence is identical to that of the mRNA (except for T in DNA and U in RNA) is called the sense or coding strand.
• The major steps which are common to both prokaryotes and eukaryotes in the process of transcription include initiation, elongation and termination. In addition to these steps, in eukaryotes the primary transcripts undergo posttranscriptional modifications such as capping, splicing, poly-adenylated tail.
• Genetic codes are triplet codons, i.e., unique combinations of three bases which codes for a specific amino acid depending on their combinations. There are 64 codons, out of which 61 codons code for 20 amino acids.
• Polyribosomes consist of several ribosomes attached to the same mRNA.
• Mutation is the alteration in the genetic material, i.e., DNA (RNA in case of a few viruses) and can be categorised as addition, deletion and substitution of one or a few nucleotide.
• High rates of mutation are not observed due to the DNA repair mechanism which could be through excision repair, mismatch repair, etc.
• Recombination is a process during which exchange of part of homologous chromosomes take place.
