lec 12 Central dogma.pptx presentation power point

Centra dogma

1. Central Dogma of Molecular B iology Lec # 12

2.   Definition “Central dogma is the process in which the genetic information flows from DNA to RNA, to make a functional product protein .“  It is often stated as "DNA makes RNA, and RNA makes protein“   Although this is not its original meaning. It was first stated by  Francis Crick  in 1957

3. What is Central Dogma? The central dogma illustrates the flow of genetic information in cells, the DNA replication, and coding for the RNA through the transcription process and further RNA codes for the proteins by translation. The concept of a sequence of interaction can be understood through the framework. The most common includes biopolymers. The major category of biopolymers include Proteins, RNA and DNA

4. T hey are further divided into general transfers, unknown transfers, and special transfers. Special transfers occur in an exceptional case in the laboratory. General transfer occurs in almost all cells. It describes the regular flow of information through transcription and translation. Unknown transfers are said never to occur

5. New discoveries and exceptions to the rule As a general rule, the classic view of central dogma of biology reflects how molecular biology data are organized within the databases ( e.g , by molecule type such as genomic DNA, mRNA, protein). However , many exceptions to this dogma are now known as a result of genomic studies in recent years . For example, much of the DNA that does not encode proteins is now known to encode various types of functional RNAs

6. Steps of Central Dogma Discovering this sequence of events was a major milestone in molecular biology . It is called the  central dogma of molecular biology . The two processes involved in the central dogma are  transcription  and  translation . In eukaryotic cells, transcription takes place in the nucleus . It uses DNA as a template to make an RNA molecule known as messenger RNA (mRNA). The RNA molecule then leaves the nucleus and goes to a ribosome in the cytoplasm, where translation occurs. Translation reads the genetic code in mRNA and makes a protein

7. Genetic code The genetic code is a set of three-letter combinations of nucleotides called codons, each of which corresponds to a specific amino acid or stop signal . The concept of codons was first described by Francis Crick and his colleagues in 1961.

8. The Reverse Transcriptase Ripple In 1970, two laboratories demonstrated biochemically that RNA could be used as a template for DNA. Howard Temin had argued that the RNA of some viruses must be copied into DNA in certain cell types in order to explain the ‘transformation’ of normal cells to cancer cells by these viruses. Detecting the enzyme responsible for this RNA dependent DNA synthesis was an important piece of evidence that convinced many former sceptics that his theory was valid.

9. One writer went so far as to suggest that existence of ‘inverted transcription’ (copying RNA to make DNA) meant that the entire central dogma needed to be re-examined. Crick responded to the challenge and a few weeks later published an expanded view of the central dogma. He reiterated that information transfer from RNA to RNA, from RNA to DNA, or perhaps even from DNA to protein (directly, without an RNA intermediate) were all ‘special transfers’ which might occur in certain cell types

10. Reverse Transcriptase Thus the newly discovered ‘reverse transcriptases ’, as the RNA-dependent DNA polymerases are now called, did not disturb the central dogma