 So, as you know the main function of DNA is the storage and transmission of genetic information. So, lot of information in heredity information is stored in the DNA molecule and then this information is transmitted to the next generation as well as this information is transmitted to the cells metabolic machinery for the synthesis of proteins. So, how this flow of information or transmission of information takes place. The central dogma outlines the flow of genetic information during growth and division of the cells. So, when the cell is growing it needs proteins. How the information coded in DNA is transferred to the proteins for the synthesis of proteins and similarly during the division of cell that means the formation of new cells. So, then again this question arises how the information stored in the DNA is copied to the new cell. Genomic information flows from DNA to RNA to proteins during cell growth. In addition all living cells must replicate their DNA when they divide. During cell division each daughter cell receives a copy of genome of the parent cell. Replication is the process by which two identical copies of DNA are made from the original molecule of DNA. So, replication occurs in the cells just prior to cell division because it is prerequisite of cell division. If the cell is going to divide it must have a new copy of DNA. An important point is that information doesn't flow from protein to RNA to DNA. It only flows from DNA to RNA to proteins however flow of information from RNA backwards to DNA is possible in certain cases due to the presence or operation of a special enzyme which is reverse transcriptase. So, reverse transcriptase catalyze the synthesis of DNA from RNA. So this is in some special cases. By the end of 1953 the working hypothesis was adopted that the chromosomal DNA functions as the template for the synthesis of RNA molecules in the cells. So, if RNA is present in the cell the DNA in the nucleus or the chromosomal DNA will act as the template for the synthesis of these RNA molecules. These RNA molecules are subsequently moved to the cytoplasm where they determine the arrangement of amino acids within the protein. So, after synthesis these RNA molecules come to the cytoplasm where synthesis of protein take place. In 1956 Francis Crick referred to this pathway for the flow of genetic information as the central dogma. So, this pathway, flowing pathway of information was called central dogma. So, this is the central dogma. So, here you can see this is DNA and the information flows from DNA to RNA during the process of transcription and then from RNA to proteins during the process of translation. So, this is during the growth of cells. However, for the replication or for the cell division the DNA must be copied and the direction is like this pre-existing DNA. An important point in the Bob equation is that the two arrows are unidirectional. So, this means that RNA sequences are never determined by protein subunits or protein templates. Similarly, DNA can never be synthesized from DNA. So, that is why the unidirectional arrows are used in this equation. The idea that proteins never serve as template for RNA synthesis has stood the test of time. However, RNA chains sometimes do act as templates for the synthesis of DNA chains of complementary sequence. So, RNA can synthesize DNA of complementary sequence. Such reversals of the normal flow of information are very rare events as compared with the enormous number of RNA molecules being synthesized on the DNA templates. So, sometimes in special circumstances as I mentioned earlier where the reverse transcriptase activity is present only there RNA can be used as a template for the synthesis of DNA. Thus, the central dogma as originally proclaimed more than 50 years ago still remains essentially valid.