Micro viruses 2 Flashcards
What are viruses ?
Viruses are sub cellular, infectious agents that are obligate intracellular parasites
What are the size of virus?
20-300nm in size - small
Why can viruses not do ?
Cannot replicate outside living cells
How can the viruses multiply ?
In order to multiply viruses have to get into a cell in
which they can replicate – a host cell
What do viruses take advantage of ?
the host cell’s metabolic machinery to create progeny virions
A broad variety of viruses contribute to human disease
What is the basic structure of the virus ?
The basic structure of a virus consists of a capsid surrounding the viral genome
What is the nucleocapsid ?
The genome and the capsid together
What is a capsid?
The capsid is a protein shell composed of repeating subunits called capsomeres
What is Icosohedral symmetry is the ?
preferred capsid morphology (20 equalateral triangular faces)
What are alternative morphologies ?
- Helical nucleocapsid
- Other virus families are surrounded by a lipid envelope (derived from the host cell membrane). The envelope is studded with glycosylated transmembrane proteins that are involved in host cell attachment
- The viral genome may be composed of DNA or RNA (single stranded or double stranded)
How can viruses be classified by ?
according to their genome type and replication strategy (Baltimore classification)
- dsDNA
- ssDNA
- dsRNA replicating via (+) sense RNA
- ssRNA (+) sense genomes
- ssRNA (-) antisense genomes- complementary sequence to messenger RNA sequence
- Diploid ssRNA
- Retroviruses (e.g HIV) (contain an enzyme (reverse transcriptase) that converts the retroviral RNA genome into double-stranded DNA.
ds = double stranded
ss- single stranded
What does the viral genome generate?
messenger RNA which is translated into proteins
what are the structures of virus like ?
different shape and forms
What is the Schematic representation of SARS-CoV-2 structure? (COVID-19)
This is an enveloped, positive-sense RNA virus with four main structural proteins, including spike (S) and membrane (M) glycoproteins, as well as envelope (E) and nucleocapsid (N) proteins.
-spike protein attaches iris to host cell
What viruses are clinically significant ?
- Respiratory viruses
1. Adenovirus (respiratory tract infections)
2. Parainfluenza virus (pharyngitis (sore throat))
3. Rhinovirus (tonsillitis and sinus infection)
4. Corona viruses (e.g SARS CoV-1, SARS CoV-2) (severe acute respiratory syndrome - Retrovirus
1. HIV (AIDS) - Papillomavirus (warts)
- Pox virus
1. Small pox
What are some more viruses of clinical significance ?
Hepatitis virus Hepatitis A-E (liver dysfunction) Childhood diseases Rubella Rubeola (measles) Mumps Herpes virus Herpes Simplex Virus (HSV-1, HSV-2), Cytomegalovirus (CMV), Epstein Barr Virus (EBV), Varicella Zoster Virus (VZV) (cold sores, glandular fever, lymphomas, shingles, acute CNS infections) HSV-1 most common cause of corneal infections
What are the strategies for infectivity and replication?
- The first stage of viral infection involves entry into the host cell
- Viruses utilise different strategies
- Attachment
- Translocation
- Genome insertion (naked virus)
- Membrane fusion (enveloped virus)
- Endocytosis and endosome formation (enveloped virus)
How is the replication of virus after entering the cell ( strategies for infectivity and replication ) ?
- Viral genome transcribed to form new virions
- Translation using host cellular machinery
- First proteins synthesised are generally DNA or RNA polymerases
- In general, DNA replication occurs in the nucleus, RNA replication occurs in the cytoplasm
What happens with retroviruses after entering the cell ( strategies for infectivity and replication ) ?
- Retroviruses are RNA viruses that convert their ssRNA into dsDNA
- Structural proteins synthesised
- Viral assembly primarily in the cytoplasm
- Release of newly formed virions
What is the life cycle of SARS-CoV-2?
SARS-CoV-2 is internalized by the cell via (i) membrane fusion or (ii) endocytosis. The SARS-CoV-2 spike binds to the angiotensin-converting enzyme 2 (ACE2) via its receptor-binding domain (RBD) and further releases its RNA (b), which will be translated into viral proteins (c,d). e–h, These proteins will form a replication complex to create additional RNA (e) that will further assemble with the viral proteins into a new virus (f), which will be released (g,h) via exocytosis
What is the infectivity of humans?
- Virus-induced pathology is the result of direct viral action leading to host cell death
- Damage can also occur due to the immune response to viral antigens
What are the routes of transmission ?
Viruses can be spread by a variety of routes:
- Respiratory droplets
- Faecal-oral
- Parenteral
- Sexual activity
What ways immune system deals with virus ?
- through antibody response - neutralise virus- antibody binds to virus to prevent virus from infecting more cells
- Mediated destruction of viruses- antibodies can mediate cell death through antibody mediator cells- cytotoxicity - once virus has been identifies in cell– get T helper cell - activates cytotoxic T cells CD8 positive cells- these induces apoptosis
What is latent infection ?
With some viruses, a latent infection can be established after a primary infection
e.g. Herpes viruses can remain latent in sensory ganglia
