The Flow of Genetic Information

The flow of genetic information follows the sequence DNA —> RNA —> protein. 

Enzymes catalyze metabolic reactions, the flow of genetic information, the synthesis of molecules that provide biological structure, and help defend us against infections and disease. 

Figure 20.18 The central dogma of molecular biology a summary of processes involved inflow of genetic information from DNA to protein. The diagram is a summary of the biochemical processes involved in the flow of genetic information from DNA to protein via RNA intermediates. This concept had to be revised following the discovery of the enzyme, reverse transcriptase, which catalyses information transfer from RNA to DNA (see Chapter 18). It may have to be modified in the future since changes in the fatty acid composition of phospholipids in membranes can modily the properties of proteins, and possibly their functions, independent of the genetic information within the amino acid sequence of the protein (See Chapters 7, 11 and 14).

As the field of molecular genetics grew, the DNA molecule became the focus of many research efforts. Francis Crick and George Gamov developed the sequence hypothesis to explain how DNA makes protein. They stated that the DNA sequence specifies the amino acid sequence of a protein and postulated the central dogma of molecular genetics the flow of genetic information is a one-way road, it always takes the direction from DNA to RNA to protein [16]. In the same year, 1957, Mathew Meselson and Frank Stahl demonstrated the replication mechanism of DNA [17]. In 1958, DNA polymerase became the first enzyme used to make DNA in a test tube. 

The flow of genetic information involves biosyntheses of DNA, RNA, and proteins, known as replication, transcription, and translation, respectively. DNA replication in prokaryotes (Nossal, 1983) and eukaryotes (Campbell, 1985) are very similar, though eukaryotic replication is more complex (DePamphilis, 1996). A... 

The central dogma, proposed by Crick in 1956, summarizes the flow of genetic information in normal cells ... 

The flow of genetic information in normal cells is from DNA to RNA to protein. The synthesis of RNA from a DNA template is called transcription, whereas the synthesis of a protein from an RNA template is termed translation. Cells contain several kinds of RNA messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), which vary in size from 75 to more than 5000 nucleotides. All cellular RNA is synthesized by RNA polymerase according to instructions given by DNA templates. The activated intermediates are ribonucleoside triphosphates and the direction of... 

Genes specify the kinds of proteins that are made by cells, but DNA is not the direct template for protein synthesis. Rather, a DNA strand is copied into a class of RNA molecules called messenger RNA (mRNA), which are the information-carrying intermediates in protein synthesis. This process of transcription is followed by translation the synthesis of proteins according to instructions given by mRNA templates. Thus, the flow of genetic information, or gene expression, in normal cells is... 

Transcription represents the most important point of attack for the regulatory processes which control the flow of genetic information from DNA to mature protein. Primarily, it is the initiation of transcription that is regulated, since this represents the rate-limiting step. The essential elements of regulation at the level of initiation in eucaryotes are (Fig. 1.13)... 

This concept has been referred to as the central dogma of molecular biology because it describes the flow of genetic information from DNA through RNA and eventually to proteins. 

Recall that according to the central dogma, the flow of genetic information is from DNA to RNA and then to protein. Retroviruses are an exception to this rule. The alterations of the central dogma that are observed in retroviruses and other RNA viruses can be illustrated as follows ... 

The flow of genetic information is from DNA to RNA to protein. In certain viruses, the flow of information is from RNA... 

The central dogma of biology suggests the direction of the flow of genetic information from DNA to RNA to protein is DNA -> RNA —Protein. 

I he virus that is responsible for the acquired immune deficiency syndrome (AIDS) is called the human immunodeficiency virus, or HIV. HIV is a member of a family of viruses called retroviruses, all of which have single-stranded RNA as their genetic material. The RNA is copied by a viral enzyme called reverse transcriptase into a double-stranded DNA molecule. This process is the opposite of the central dogma, which states that the flow of genetic information is from DNA to RNA. But these viruses reverse that flow, RNA to DNA. For this reason these viruses are called retroviruses, which literally means "backward viruses." The process of producing a DNA copy of the RNA is called reverse transcription. 

---