Lecture 11 - Viruses Flashcards
What are viruses?
Viruses may be defined as a cellular organisms whose genome consists of nucleic acid, and which replicate inside host cells using host metabolic machinery to form a pool of components that assemble into VIRIONS to transfect other cells.
Explain the physical structure of viruses
Viruses are small in size 20-350 nm being able to pass through 0.22𝜇m filters. They contain either a single or double strand or either RNA or DNA which is enveloped in a capsid. The capsid is enclosed by an envelope with glycoproteins which allow the virus to bind to their host cells, promoting viral entry into the cell. There are viruses that do not contain the envelope and are referred to as naked capsid viruses. The regular shapes that viruses contain are sphere, helix and icosahedron.
What are virions?
Virions are virus particles that inert carriers of the genome within the cell which does not grow or form through cell division. Virions carry the viral genome from cell to cell protecting it from inhospitable environments.
Describe the difference between enveloped and non enveloped viruses
Enveloped viruses contain proteins which have two main types - glycoproteins and matrix protein. These viruses are released by budding and cell lysis and are environmentally sensitive to acid, detergent, desiccation and heat. As a result the viruses must remain in moist environments, cannot survive in the GIT and does not always kill the cell to disseminate, has protection from the host immune system.
Non-enveloped viruses are hydrophilic which protects the virus from organic solvents. They are environmentally stable against temperature, acid, proteases, detergents and desiccation. As a result of these properties the viruses easily spread, retain infectivity after drying, are resistant to detergent and sewage treatment, survive in the gut and induce immune response.
Give example of a virus that causes a specific disease. Describe its causes
A virus that can causes a specific disease is Norovirus responsible for Gastroenteritis. Norovirus is usually referred as a foodborne pathogen that causes food poisoning. The incubation time is generally around 1 -2 days causing vomiting and diarrhoea fever and malaise.
Describe the ‘lifecycle’ of a virus. HEPC
The virus binds onto the host cell that is unique to the proteins on the envelope and internalizes
Cytoplasmic release and uncoating - becomes the template for synthesis of complementary viral strands.
Internal ribosome entry site - mediated translation and polyprotein processing
DNA replication
Packing and assembly - Maturation and release
