Summary of Viruses MINDMAP PDF

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Summary

Viruses SUMMARY MINDMAP
- Structure and function
- HIV
- Ebola
- Influenza
- Replication cycle
- Role in Cancer
- Prions...

Description

Relevance of viruses

Ebola

INDIRECT EFFECT: viruses infecting farmed animals - economic & food security issues for public health" ! - E.g. Tobacco Mosaic Virus (TMV) can indirectly affect other crops

Influenza

• Characterised by fever, weakness, muscle • Influenza A/Seasonal Influenza pain followed by internal and external is a viral infection affecting the bleeding" lungs & airways" • The virus is transmitted to people from wild • Complications include bacterial animals & spreads in the human population pneumonia and can be fatal H2H transmission" especially in older people & • Average fatality rate = ~50% those with certain underlying health conditions

Human Immune Deficiency Virus (HIV)

• HIV infection causes AIDS - fatal disease if untreated" • Infects both sexes, spreads worldwide and causes immune deficiency" • Community engagement - key to controlling outbreaks" • Immune deficiency = opportunistic infections become harmful" • Early supportive care with rehydration & symptomatic • If left untreated, the immune system becomes too damaged to treatment improves survival defend against infections

Virus characteristics Microscopic" Acellular" Infectious agent" Causes many infections of humans, animals, plants and bacteria" • Causes many of the diseases that plague the world

• • • •

Extracellular state: • Called virion" • Some have phospholipid envelope" • Outermost layer provides protection & recognition sites for host cells" • Protein coat (capsid) surrounding genome (nucleic acid)% Nucleocapsid = nucleic acid + capsid Intracellular state: • Capsid removed" • Virus nucleic acid released

Viruses All genetic information is limited by the size of the capsid and so do not have space for junk DNA

• Development in lower respiratory tract - more harmful than upper in seasonal influenza" • Complications of A(H5N1) and A(H7N9) infection include hypoxemia, multiple organ dysfunction & secondary bacterial & fungal infections

Capsid morphology Capsids = Protein coats that provide protection for viral nucleic acid & attachment site to host’s cells" • Composed of proteinaceous subunits called capsomeres" - Capsomeres may be made of single or multiple types of proteins

• Damage to the cell from the replication of Genetic material of viruses virus & our own immune response to the virus cause symptoms of disease" • May be DNA or RNA, but never both" - Can be dsDNA, ssDNA, dsRNA, ssRNA" • Mechanisms to replicate the viral genome differ from mechanisms to ‣ ss = single-strand, ds = double-stranded " replicate host genome so are excellent • May be linear and segmented or single and circular targets of drug design

Zika virus

Flavivirus: enveloped, ssRNA

ZOONOSIS = Transfer of virus from one species to another • Could be relatively benign in animals but deadly to man" • Results in AIDS, Influenza & Ebola • Cell surface protein on envelope called Haemagglutinin, Neuraminidase • Various types: H1, H2… N1, N2…" • H1 N1: currently common type causing influenza

Stages of lytic replication cycle 1. 2. 3. 4. 5.

Attachment Entry Synthesis Assembly Release

Viral replication with period latency Replication of animal viruses • Same basic replication pathway as bacteriophages" • Lysogeny/latency • Differences result from:" • Modified replication cycle (there is a pause)" - Nature of animal cells - e.g. no cell wall" • Infected host cells grow & reproduce normally - Some viruses are enveloped - leads to different entry for generations before they lyse" mechanisms" • Lysogenic conversion results when phages carry genes that alter phenotype of a bacterium - Viruses have glycoprotein spikes or other attachment molecules that mediate attachment to cells THREE mechanisms of entry of animal viruses A. Direct penetration B. Membrane fusion - Viral glycoproteins remain in cytoplasmic membrane" C. Endocytosis - Cytoplasmic membrane of host engulfs virus

Role of viruses in cancer Viruses cause 20-25% of human cancers" • Some carry copies of oncogenes as part of their genomes" • Some promote oncogenes already present in host" • Some interfere with tumour repression when inserted into host’s repressor gene • Specific viruses are known to cause ~15% of human cancers"

Viruses

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Process of budding in enveloped viruses - viruses also have to leave cell to infect more cells

Replication of animal virus genomes • DNA viruses often replicate in the nucleus" • RNA viruses often replicate in the cytoplasm

Cervical cancer Burkitt’s lymphoma Hodgkin’s disease Kaposi’s sarcoma

Culturing viruses in the lab Characteristics of prions • Culturing viruses in mature organisms • Normally, nearby proteins & polysaccharides force PrP • In bacteria" (prion protein) into cellular shape" • In plants and animals" • Excess PrP or PrP mutations result in formation of • Ethical and safety considerations prion PrP" • Culturing viruses in embryonated chicken eggs - Cause newly synthesised cellular PrP to refold into Characteristics of viroids • Inexpensive, among the largest of cells, free of prion PrP" contaminating microbes & contain a nourishing yolk" • Prion diseases" • Extremely small, circular pieces of RNA that are infectious & - Fatal neurological degeneration, fibril deposits in • Safety considerations brain, loss of brain matter" pathogenic in plants" • Culturing viruses in cell (tissue) culture - Large vacuoles form in brain" • Similar to RNA viruses, but lack • Safety considerations - Spongiform encephalopathies - BSE, vCJD, kuru" capsid • Prions only destroyed by incineration or autoclaving in • May appear linear due to H 1 N NaoH bonding...