 Now, let's look at the central dogma of molecular biology. The dogma states basically that DNA contains the information, genetic information, heritable information, which is transmitted from one generation to the next. That information is used to make a molecule of RNA, which contains now the same information that DNA contained originally. This RNA can be used to form protein. Once the information has been passed on to proteins, you cannot retrieve that information. And also, DNA can replicate itself because we need to have continuity of that information for the next generations. So, this dogma raised two serious questions. In eukaryotes, we know that DNA is in the nucleus, whereas proteins are synthesized in the cytoplasm. So, how is it that the information, genetic information, is moved from DNA, which is present in the nucleus, to RNA? We know DNA doesn't physically move to the cytoplasm itself. The second question that rose was what is the relationship between a specific nucleotide sequence of DNA and a specific amino acid sequence in a protein? Basically, how is the language of nucleotides converted or translated into the language of amino acids? Amino acids, as we know, make the proteins, which ultimately do the work or they perform the functions, which are coded by DNA, to begin with. So, Dr. Crick, he's the same gentleman who, along with Dr. Watson, came up with the structure of DNA. He proposed hypotheses, the messenger hypotheses and transcription. He proposed that RNA molecule forms a complementary copy of one of the DNA strands. This RNA physically then moves to the cytoplasm where it serves the template. It is still in the form of the nucleotide sequence. It serves as the template, which can then be translated into the language of amino acids. Secondly, the second question we had was how the translation takes place. So, Dr. Crick proposed an adapter, a molecule that can bind a specific amino acid with one region and can recognize sequence of nucleotides within another region to translate the language of DNA into language of proteins. So, adapter would have ability to bind, interact with amino acids, which are the basic building blocks of proteins and another domain should be able to recognize specific nucleotide sequence on the messenger RNA. So, this is the overview. DNA is inside the nucleus. RNA is formed. It moves outside the nucleus. This type of RNA is called the messenger RNA because it is carrying the message of DNA from the nucleus to the cytoplasm. Here, RNA is encounters ribosomes. We already know that these are the organelles that interact with messenger RNA and they produce a protein which is coded by messenger RNA which was originally coded by the DNA. Here, I feel pertinent to mention the exceptions to the central dogma. There are viruses that are exception to that rule, DNA containing information. The information getting converted into RNA and ultimately being translated into protein. For example, influenza and polio virus, their genetic material is not DNA. It is an RNA molecule. That RNA molecule, when these viruses infect a cell, that RNA molecule makes many copies of itself and also makes RNA translated into viral proteins. Viral proteins are required to contain the nucleic acids which I have the genetic information. So, viruses, as we know, have proteins and the nucleic acids. The other exception is HIV, human immunodeficiency virus, the virus that causes AIDS, acquired immune deficiency syndrome. This virus, the genetic material of this virus is also an RNA molecule. But this RNA does not get converted into another RNA molecule or it doesn't get converted. RNA does not copy itself like the influenza virus. This RNA is first converted into DNA. This DNA can integrate into the host genome and from where, like other genes, are transcribed, converted into RNA into a protein that can then happen. But first, this RNA virus has to convert its RNA into DNA and then from that DNA, it makes more RNA and some of that RNA is used to make new proteins. So, these are the two exceptions but ultimately the dogma that DNA contains information communicates that information to RNA which gets translated into protein pretty much holds.