Unformatted text preview:

Lecture #6Viruses• the ultimate life form• (next to prions) • Cat has not sense of balance b/c his cerebellum did not develop fully • ClassificationGenome *:single stranded OR double stranded*DNA OR RNA*unipartite* or multipartite (‘segments’)Enveloped *or non-enveloped*alsoVirus particle shape spherical, cylindrical, etc.Size (really really small)Nuclear OR cytoplasmic - Virus are very simple organism- consist of a genome either DNA or RNA - some are enveloped and some non- All of them have a protein coat around the genome- Some of them in addition have envelope around them - the main way to classify is the structure of its genome and if it has a envelope or not• The Lytic Cycle : dsDNA virus(dsDNA virus; Herpesviridae, Papilomaviridae, Poxviridae etc.)1. Adsorption - tail fiber or spikes/receptor2. Entry a) non-enveloped - endocytosis b) enveloped - fusion3. uncoating release of nucleic acid from protein coat- Focus on the steps of the lytic - 1. adsorption- very specific process- 2. entry- virus has to get into the cell - if it is non-enveloped it comes in by endocytosis tricks the cell. - if its enveloped it comes in by fusion. Cell membrane fuses with the envelope after adsorption, and that’s how the virus gets in- in either case the virus gets into the host cell- 3. the genome has to be released by the protein coat. The virus gets in the protein coat falls apart and that releases the genome into the cell. The viral genome is then replicated and the genome is expressed to give you more protein coat 4. genome replication/expression (txn/tla) transcribed replicate viral genome (nucleus) (host enzymes) transcribe viral genome (nucleus) (host enzymes) translate viral proteins (cytoplasm) (host enzymes) 5. Maturation - assembly of mature virus particles (new genomes + new coats) (cytoplasm)6. release of new virus particles - lysis (kills host) or budding (exocytosis) (may kill host cell eventually)In the lytic cell, the cell is taken over, produces viruses with its own machinery and organelles, and then dies, releasing more viruses• Expressed transcribed into RNA - The host cell can copy - DNA into DNA- DNA into RNA- RNA into protein- viruses want to have the smallest genome as possible - - CANT go RNA to DNA or RNA to RNA - 5. Maturation/assemly: you make thousands of new virus particles and then the virus particles get out of the cells but either budding or lysis - A non enevelope virus: lysis the cell, breaks the cell open and that’s how it gets out of the cell. That immediately kills the cell. - An eneveloped virus: which gets released by budding which is the reverse of endocytosis, it gets bud off at the surface, and releases the virus. That enventually kills the cell. • SummaryAdsorptionEntryUncoating Genome replication/expressionMaturationRelease• Adsorption: contact between the 2• Entry: release of the cell• Note:Adsorption – a very specific interaction between the viral coat or envelope and the host cell’s plasma membrane that largely determines host range (receptor corruption)(i.e. T4/LPS ; rhinovirus/ICAM-1 ; HIV/CD4 ; etc.)• Viruses w/o Receptors go to…Viruses w/o receptors Cannot replicate. It eventually dies out. • The Lysogenic Cycle(dsDNA virus)1. Adsorption2. Entry3. Uncoating 4. Integration of viral genome into host chromosome (nucleus) (lysogeny) (viral integrase) 5. Virus remains quiescent in the host chromosome for some period of time• Very much the same but instead of getting genome replicate/expression you get integration of viral genome • Human cells don’t know how to do integration b/c it requires a gene of enzyme called integrase (EXCISSION) 6. Excision – virus genome excises itself from the host chromosome (viral enzyme)7. Expression - replicate viral genome (host enzymes)transcribe viral genome (host enzymes) translate viral proteins (host enzymes) 8. Maturation - assembly of mature virus particles9. release of new virus particles - lysis (kills host) or budding (exocytosis) (may kill host celleventually)• Summary lysogentic cyle AdsorptionEntryUncoating Integration/Quiescence/Excision (min. to life)Genome replication/expressionMaturationReleaseThese are all double stranded DNA so far. • dsDNA virus Genome replication (done by host enzymes) dsDNA dsDNA RNA genome expression (done by host enzymes) new virus particles Coat Proteins• What about other types of viruses?dsDNA ssDNA *dsRNA *ssRNA (+/-) ***** retro viruses ***• The most stable one is the double stranded DNA. - b/c sinc there are 2 strand, if one gets messed up, (wrong letter) the other strand is there to tell you what letter really belongs there, and it can be fixed. - double RNA - even though it has the 2 strands, RNA is less stable than Dna. One reason they are less stable is b/c of RNA polymerase is error prone, pretty much RNA gets replicated into RNA, and that enzyme is more likely to make mistakes and when you have two even more prone to mistakes. - and the same goes for single stranded RNA- The least stable of all is retro viruses • ssDNA Viruses(Parvoviridae, etc.)1. Adsorption2. Entry3. Uncoating 4. Second strand synthesis ssDNA-->dsDNA (Host Enzymes)5. Genome replication/expression (or lysogeny) (host enzymes) 6. Maturation7. ReleaseSingle stranded DNA is not much different than double stranded other than that extra step to make the double strand • ssDNA Viruseshttp://www.mcb.uct.ac.za/tutorial/dnagen.htm• SS DNA Virus host enzymes ssDNA dsDNA genome replication stage RNA new virus host enzymes genome expression stage particles Protein • Single stranded RNA are more complicatedIf you have a RNA molecule that can be translated to protein its sense If don’t have rna molecule that can be translated its antisenseSo antisense have to first be • ssRNA Virusesss (+) RNA Viruses (messenger) (sense)Flaviviridae [Hepatitis C, West Nile] Picornaviridae [Polio, Hepatitis A, Rhino]Togaviridae [Rubella]ss (-) RNA Viruses (anti-sense)Filoviridae [Ebola/Marburg], Paramyxoviridae [Measles, Mumps]Rhabdoviridae [Rabies] • ss(+) RNA Viral Replication1. Adsorption2. Entry3. Uncoating 4. Replication/Expression: ss(+)RNA à many ss(-)RNAs(*RNA


View Full Document

KSU BSCI 20021 - Lecture #6 Viruses

Download Lecture #6 Viruses
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Lecture #6 Viruses and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lecture #6 Viruses 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?