Lecture 7: Viruses Flashcards
characteristics of viruses and bacteria
Viruses
◦ Very small: 20 to 300 nanometres
◦ Visible only under electron microscopy
◦ DNA or RNA genome
◦ No cell wall
◦ Lack the normal cellular machinery of living
cells (for example no ribosomes)
◦ Obligate intracellular parasites
◦ Utilise the host’s cellular machinery to
reproduce
Bacteria
◦ Larger: 1000 to 2000 nanometres
◦ Visible under regular light microscopy
◦ DNA genome
◦ Cell wall
◦ Possess the normal cellular machinery of living
cells
◦ Can survive outside a host
◦ Able to replicate independently of the human
host
3 parts of virus
- Genetic material (DNA or RNA)
- protein coat that protects these genes
- sometimes, am envelope of lipids that surrounds the protein coat when they are outside of the cell
Describe the genetic material part:
what does it have, purpose
Nucleic acid core: At the core of viruses is the genetic material that encodes the transcription of all viral components, mostly proteins (such as enzymes. This is genetic material is either DNA or RNA, never both. It can be single or double stranded
The genetic material is the software program for making copies of the virus
Describe the protein coat part:
what does it have, purpose
Surrounding the core is a protective coating made of protein, the capsid. The capsid is rigid and determines the shape of the virus. It is made from repeating protein units called capsomeres
The capsid and its nucleic acid core together form the nucleocapsid
Describe the envelope part:
what does it have, purpose
Envelope:
Usually spherical because their envelopes unlike capsids are loose fitting
Envelopes are lipid bilayers that contain phospholipids, cholesterol, proteins. Some of these proteins incoperate carbs and thus are glycoproteins which usually proturde out of envelope as spikes. They attach to host cell surface receptors to allow entry
No envelope are naked viruses
CLASSIFICATION
based on
1. type of nucleic acid present
2.single or double stranded
3. presence or absence of envelope
what is the + and - sense strand
+ = sense strand = translatable code from 5’ to 3’ direction
- antisense = translatable in 3’ to 5’
Virus structure: example of the 3 types and example of them
- Cubic
Adenovirus (isohedral, 20 sided, protein shell with nucleic acid contained within - Helical
TM (elongated nucleocapsid rod shaped, capsomeres arranged around a spiral of nucleic acid
3.Complex - Poxvirus
Viral reproduction
why cant they reproduce themselves
Unable to reproduce themselves, as they lack the normal
cellular machinery of living cells (for example no ribosomes)
They must infect us and use our cellular machinery to
reproduce
steps of replication
- Union phase
- Penetration phase
3.transcription phase
4.Synthesis phase
5.assembly phase
6.release phase
Transmission routes types and example
Droplets (aerosols); influenza,
corona and rhinoviruses
Faecal oral; norovirus
Animal vectors; dog bites for
Rhabdoviridae (rabies
virus)
Insect vectors;
arboviruses
Bodily fluids;
semen (HIV)
blood (HBV)
saliva (EBV)
breast milk (HCV)
Vertical; mother to child
in utero (HIV)
Fomites (physical
objects)
coronaviruses
what is Viral tropism
The ability of a virus to infect a target cell of the host, using a specific receptor to gain entry to the cell
The DISEASE, TARGET, RECEPTOR for…
Epstein Barr (EBV), HIV, influenza, Rhinovirus, Covid
Epstein Barr (EBV)
Disease: Infectious mononucleosis Burkett’s lymphoma
Target: B cells
Receptor: Complement C2
Human immunodeficiency (HIV)
Disease: Acquired Immune Deficiency syndrome (AIDS)
Target: T cells and monocytes
Receptor: Cluster of differentiation (CD): CD4
Influenza
Disease: Influenza (flu)
Target: Respiratory epithelium
Receptor: Sialic acid residues
Rhinovirus
Disease: Common cold
Target: Nasal epithelium
Receptor: ICAM
Covid
Disease: Covid-19
Target: Lung epithelium
Receptor: Angiotensin converting enzyme 2
(ACE2)
Immune Response:
Viral versus bacterial infection
Viruses
◦ Intracellular infection
◦ Phagocytes cannot “see” the pathogen
inside the host cell
◦ Phagocytosis cannot be used to
eliminate viruses
◦ But virally infected cells can display viral
protein on their cell surface, using MHC
◦ So T cells can “see” them
Bacteria
◦ Most species = extracellular infection
◦ Phagocytes recognize the bacterial
PAMPS using their PRR
◦ Phagocytosis is an effective mechanism
to kill the bacteria
how do Virally infected cells display viral peptides
via MHC to cytotoxic T cell TCR
