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Microbiology and Immunology
Microbiology and Immunology 2500A/B

An Intro to Molecular Biology – Mar. 8, 2013 Part 1: Genes  What is common between almost everything in the world? All have nucleic acid Virus: some have their genome in the form of RNA Animal Cell Genome that duplicates the cell are all contained in the nucleus o oHumans have 23 chromosomes Human Genome Project 23 pairs of chromosomes contain DNA 3.3 billion base pairs  Approximately 35, 000 genes - these are all identifiable genes that can produce proteins Total length of DNA : 1 x 10^10 Km Total length can do 33 round trips to the sun or wound up the earth 250, 000 times Genes • Can produce a protein • Chromosome has DNA & DNA carries the gene • Gene is composed of 4 different bases  G - Guanine C - Cytosine   A - Adenine  T - Thymine  or in RNA U - Uracil instead of thymine • Most DNA exist as double stranded form • Some viruses exist as single stranded forms • G & A have hydrogen bonds that bind them • C & T have 2 hydrogen bonds that bind them • Groups are bound in chains by sugar phosphate groups • DNA replicates semi-conservatively  Only replicates in one direction, from 3’ to 5’  In order to copy, DNA has to unwind then one strand goes up and another strand goes down b/c it only copies from 3’ to 5’ direction  Product is 5’ to 3’ (replicate opposite, bind opposite direction) Pathway of Information Flow in DNA Virus Replication oDNA can exist as dsDNA or ssDNA ossDNA has to go through dsDNA intermediate to make more ssDNA - aka virus oIn cell, dsDNA is transcribed to make mRNA which is translated to make a protein oViruses are either ssDNA or dsDNA Classification of RNA Virus Genomes - Single-Stranded RNA Viruses  Positive sense RNA viruses - can be translated to make proteins  Negative sense RNA viruses - complementary to the positive sense  Ambisense RNA viruses - contains both positive & negative sense - Double-Stranded RNA Viruses Some small group of viruses contain dsRNA  Pathways of Information Flow of RNA Viruses  In order to make a protein negative ssRNA, you have to make complementary positive ssRNA which can then be translated from positive ssRNA  Normal cells don’t hold RNA dependent RNA polymerase - unique to RNA viruses, not in the normal cells (WILL ASK THIS QUESTION)  If is positive ssRNA, it can be translated right away & therefore doesn’t have to carry RNA polymerase in virus particles b/c as they get into cells they can translate genomic RNA to become RNA polymerase (few exceptions but this happens in most cases)  ssRNA virus makes mRNA positive which can be translated to make protein  ssRNA positive make dsRNA as intermediate  One unique RNA virus called retrovirus which is positive ssRNA virus but makes DNA intermediate during replication of this virus  One that goes through DNA intermediate is retrovirus - makes DNA with RNA they carry  Reverse transcriptase containing virus? aka is positive ssRNA that contains RNA polymerase Negative ssRNA viruses must make messenger RNA therefore they have to carry RNA  polymerase  If positive ssRNA. can be translated as they get into the cell & therefore don’t need to carry enzyme into particles Types of Mutation • Several types of mutations  Deletion of chromosome, section of DNA that’s deleted  Duplication of chromosome, section of DNA that’s duplicated  Inversion of chromosome, section that’s taken out & turned around  Insertion: Insertion of extra chromosome  Translocation: Some of these mutations can give different types of diseases Part 2: Expression of Genes  Either DNA or RNA has to be expressed to make proteins  Animal cell - gene expression takes place in nucleus The Central Dogma of Molecular Biology • Unidirectional information flow • Before discovery of enzyme that converts DNA back to RNA was unidirectional flow, therefore have DNA to RNA to protein - unidirectional information flow in this biological system • DNA exists as dsDNA & is trying to transcribe to make mRNA, mRNA is transported from nucleus to cytoplasm which is then translated to make a protein Exception!! • Reverse transcription by RNA dependent DNA polymerase (reverse transcriptase) = RNA -> DNA • Exception of the unidirectional information flow - discovery of this enzyme changed the central dogma, discovered in 1970 DNA is Made Up Of.. oEither  RNA - ribonucleic acid  DNA - deoxyribonucleic acid oNitrogenous bases oSugar phosphate backbone oBase pair Uracil (RNA) Basic difference between RNA & DNA is U base Methyl group from T is now hydrogen on U Deoxyribose from T is now only ribose on U Transcription Transcription takes place in the nucleus - can be transcribed from promoter (DNA contains promoter), sigma factor governs the transcription of these DNA Initially, RNA is made out of DNA  Unwinding of DNA & one of the strands is copied to make transcription Initiation, Elongation, Termination 5’ 7mG Capping - protected 5’ end 3’ polyadenylation - adding the adenine  All eukaryotic messenger RNAs contain poly A sequence at the 3’ end  Protects mRNA from the degradation governed by the RNAs mRNA Splicing • mRNA are formed, cleaved partially to make functional messenger RNA • Not entire mRNA is translated • Introns are put together & exons are put together as functional mRNA • mRNA is spliced so cap-s1 is exon & s2-a1 are put together to make functional mRNA* • Splicing just takes out parts of mRNA we don’t want to translate - par
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