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Unformatted text preview: Lecture 1: Central Dogma theory of DNA: 10/09/2009 Crick's idea was that genetic information was stored in DNA which is transcribed into RNA and then translated into protein which performs activity in the cell. mRNA was not discovered yet, but they already postulated that RNA is the intermediate Transcription : using DNA as a template to make a RNA copy that is written in the same language . The DNA stays in the nucleus while the RNA does work outside. Translation : when RNA/DNA language is converted into the language of amino acids. From nucleotide sequence to amino acid sequence. Crick says that Protein CAN NOT go back to DNA. Only one direction. Reason for this is that mutations in the DNA could lead to the mutation in protein. But if a mutation occurs during the translation process (a wrong tRNA brings the wrong amino acid to create a mutant protein for example) there is no way to identify the original DNA sequence from just looking at the sequence of amino acids. If you have a mutant protein, it doesn't necessarily reflect a mutation in the original DNA. This corresponds with Darwin's theory. A mutation in the genotype always produces a novel phenotype, but a new phenotype doesn't mean there was change in genotype. For example: If you get muscular from working out, it doesn't mean you're changing your DNA. It is just a adaptation. DNA replication Most cells store their genetic information, but there are some single stranded RNA virus (pomeo virus or influenza virus for example) that have a RNA genome and replicate through RNA intermediates. in 1979, it was discovered that some RNA virus' that cause tumours (retrovirus) contain an enzyme called reverse transcriptase that uses a mechanism to make a DNA intermediate before going back to RNA. so DNA <---- ----> RNA, but so far can't prove Protein doesn't go back to RNA Example of this is the AIDS virus. First thing was to sequence its RNA. Just by sequence they could tell it was a retrovirus. The RNA vrius do not have a proofread mechanism, so they can mutate much quicker than DNA. This makes it hard to create drugs that target specific RNA. Once thought that Yeast had RNA genomes because they have such a small DNA genome. It is only 50% longer than E.Coli genome. These retrovirus only affects eukaryotic cells, not prokaryotic cells. There is evidence that eukaryotic cells also carry out reverse transcription Look at figure 1.16 of Gene IX phage T4 is a double stranded DNA virus. Phage means to eat. So when a phage infects a virus, it lyses it opens, giving the illusion that it is eating the bacteria. E.Coli is used because of two reasons: if can provide it's own genetic material but it can be infected by a wide variety of phages: DNA and RNA. The genomes of these virus can recombinate with with the E.Coli to figure out the function of genes....
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