Virus cell structure

Question 1

6 properties of viruses

Answer 1

1. They are not cells (they are acellular)
2. Carriers of genetic material (RNA or DNA)
3. Require a host cell for replication
4. Obligatory intracellular parasites (self assembly)
5. Cause diseases (in humans,plants-destroy crops-, insects and bacteria-bacteriophage; they are important for us as they kill bacteria in our body)
6. Difficult to treat because viruses replicate so an antiviral has to penetrate inside the cell and kill virus

Question 2

Morphology and size of viruses

Answer 2

Viruses vary greatly in size and morphology

Question 3

Viral envelope

Answer 3

• surrounds the viral capsid in some but not all viruses (e.g HIV, herpes and influenza are all surrounded by cell envelope)
• derived from portions of the host cell membrane (cytoplasmic membrane, cell nuclear envelope, Golgi apparatus and endoplasmic reticulum)
• all envolpes are made of phospholipids but they don’t have proteins embedded in them
• enveloped viruses are susceptible to desiccation (low survival in the environment) and physical (heat) and chemical (disinfectant) challenges therefore enveloped viruses don’t survive well
• it contains host proteins and also virus encoded proteins (this is what makes viruses specific; viruses which infect bacteria won’t infect humans)
• it is responsible for viral entry into the host cells (recognition of host cell receptor and initiation of entry by fusion or endocytosis) - fusion of viral cytoplasmic membrane with host cytoplasmic membrane to release capsid
• it is responsible for viral exit from the cells= budding

Question 4

Viral capsid

Answer 4

• virus building blocks -proteins- are assembled to form a tight shell (capsid). Capsid = protein shell that encloses the nucleic acid
• capsid is made of structure units (these are the smallest functional equivalent building units of the capsid).
• capsomere=subunit of a capsid (it is formed by individual proteins fitting together like the piece of the puzzle)
• inside capsid, nucleic acid genome lodges for protection
• capsid may take the form of a polyhedron (ususally icosahedral) or it may be spiral (helical symmetry)-nucleic acid is tightly bound to proteins in capsid- or it may be more complex

Question 5

Viral genome

Answer 5

• either DNA or RNA but can be single or double stranded DNA or RNA
• circular, linear
• dictate viral genome expression -translation
• differences in the genome dictates how virus will replicate

Question 6

Viral receptors

Answer 6

• glycoproteins (virus encoded) on the surface of the envelope or ptotuding from the capsid serve to identify and bind to the receptor sites on the host’s membrane
  e. g: haemagluttinin (influenza) , GP 120 (HIV)
• receptors are unique to proteins

Question 7

Which viruses are efficient in producing new viruses?

Answer 7

-pentamers; not much energy is rewuired to form this structure. Therefore viruses with this configuration are efficient in producing new viruses

Question 8

Purpose of virus

Answer 8

-to make more viruses therefore genetic material in the viral genome needs to be transcribed into mRNA so you can form proteins therefore mRNA is key in viruses and if you destroy the viral genome, virus will die

Question 9

Why is mRNA inportant?

Answer 9

-it is key for classification of viruses

Question 10

Viral tegument

Answer 10

• a cluster of proteins that line the space between envelope and nucleocapsid of all herpesviruses
• aids in the viral DNA replication
• evasion of the immune response (inhibition of signalling in the immune system and activation of interferons)