Virology Lecture Notes

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Microbiology and Immunology
Microbiology and Immunology 2500A/B

Kang Lecture 1 An Introduction to Molecular Biology 11072012 Part 1 Genes Simplest of living organismsvirus About 10000 nucleotides in the genomeVirus is unique as some have genome in the form of RNANucleus contains genome Human Genome o 33 billion base pairs o Approximately 35 000 genes 10o Total length of DNA 1 x 10 km In humans 23 pairs of chromosomes o Contains DNA o Helps human genome reveal that there are 33 billion base pairs which contain approximately 35 000 genes Most DNA is in double stranded form some viral DNA exist as a single stranded form Replication of DNA is semiconservativedirection of copy of DNA is only in one directionsynthesizes from 3 to 5 In order to copy this DNA it has to be unwindone strand goes up and another strand goes down Single stranded DNA is copied to make double stranded DNA viral pathwayIn the cell double stranded DNA is transcribed to make mRNA which is translated to make proteins cellular pathwayUnique property of virusesconsist of RNA in their genomeClassification of RNA virus genomessingle stranded and doublestranded RNA viruses Single stranded RNA viruses can exist aso Positive sense RNA virusescan be translated to make proteins Enters cell as functional mRNA o Negative sense RNA virusescomplementary RNA strand contains positive sense Has to be transcribed to make functional mRNAo Ambisense RNA virusesone strand has positive and negativeContains both polarities Normal cells do not carry RNAdependent polymerase exam questionUnique RNA virusretroviruso Reverse transcriptase containing RNA virus Positive sensecan be translated as they get into the cell therefore do not need to carry the enzymePart 2 Expression of Genes Unidirectional flow from DNA to RNA to proteinknown as central dogma Transcription o Both strands can be copied so that there is an increased capacity to make mRNA First modification of mRNA is 57mG Capping o Protect 5 end of nucleic acid Second modification of mRNA is 3 polyadenylation o Protect mRNA from degradation governed by RNAThird modification of mRNA is splicingo Entire RNA is not translated cleavage occurs introns versus exons Introns are not used for translationExons are spliced to make functional mRNA Why do cells do this This can be used in many different ways to make many different functional mRNAsincreases capacity of the genes Capacity to modify our genes so we can make various antibodiesException to central dogma RNA dependent DNA polymeraseRNADNA Part 3 Protein Synthesis and PostTranslational ModificationEssential components for translation o mRNAMessenger RNA mRNA o tRNAo ribosomesThree nucleotides make one amino acidtRNA contains anticodon which recognizes specific codon on mRNASome amino acids have many codons that code for the same amino acid whereas some only have a single codon o MethionineAUG where as leucine has 6 various codonsRibosomesynthesizes proteins o Light subunit and heavy subunitElongation of polypeptidesprocess repeats until reaching a stop codonAmino terminus and carboxyl terminus linked with peptide bondsmake polypeptides Some proteins have posttranslational cleavagelose amino terminus by cleavage of the N terminus amino acids which is why some proteins do not start off with methionineGlycosylationadding sugars after translation is completed Phosphorylationsome proteins contain phosphate groupsProteolytic cleavagecleavage takes place in the cytoplasm with enzyme known as peptidaseOnce cleaved properly it can fold to make primaryquaternary structure to make functional proteins Folding of the protein is very important for the function of a protein Protein structure o Primary protein structuresequence of a chain of amino acids o Secondary protein structureoccurs when the sequence of amino acids are linked by hydrogen bonds o Tertiary protein structureoccurs when certain attractions are present between alpha helices and pleated sheets o Quarternary protein structureprotein consisting of more than one amino acid chain Virus needs living cells to replicatethey are obligate intracellular parasiteso Cannot replicate in the absence of host cell host cell provides all the enzymes and translational machinery to replicate the virus Kang Lecture 2 An Introduction to Human Viruses 11092012January 1 2011 world population7 074 158 000 o WHO estimated 57 million deaths per year o 20 million deaths due to infectious and parasitic diseases 35 of total deaths o 13 of 20 million deaths due to viral diseases 65 of infectious and parasitic diseasesVirusDefinition of virusobligatory intracellular parasiteClassification of virus o Replication depends on whether the viral genome is
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