Virology 2 Flashcards
Characteristics used to define virus taxa
- Capsid structure
- Enveloped/naked
- Gene expression programme
- Host range
- Pathogenicity
- Genetic similarity
Central dogma of molecular bio
DNA -> RNA -> protein
- Replication (DNA -> DNA)
- Transcription (DNA -> RNA)
- Translation (RNA -> protein)
What does the updated central dogma include
- Reverse transcription at transcription stage also
- RNA replication (RNA -> RNA) - done by RNA dependent RNA polymerase
(as opposed to DNA replication - DNA -> DNA by DNA polymerase)
How does the baltimore classification divide viruses
- Into 7 classes
- Based on genome content & gene expression strategy (how mRNA is produced)
Genome type & examples of Group 1 viruses
- Double stranded DNA viruses (dsDNA)
- dsDNA genome
- Eg: herpesvirus, adenovirus, poxviruses
Genome type & examples of Group 2 viruses
- Single stranded DNA viruses (ssDNA)
- ssDNA genome - serves as a template for transcription
- Eg: parvovirus
Genome type & examples of Group 3 viruses
- Double stranded RNA viruses (dsRNA)
- dsRNA genome
- Eg: reovirus
Genome type & examples of Group 4 viruses
- Positive sense single stranded RNA viruses (+ssRNA)
- Single stranded genome - functions as mRNA upon entry into host cell
- Eg: coronaviruses, flaviviruses, picornaviruses
Genome type & examples of Group 5 viruses
- Negative sense single stranded RNA viruses (-ssRNA)
- Single stranded RNA genome that is complementary to mRNA
- Eg: influenza virus, paramyxoviruses
Genome type & examples of Group 6 viruses
- Reverse transcribing viruses
- Use reverse transcriptase enzyme to convert RNA genome into DNA upon infection
- Eg: HIV - ssRNA genome that is reverse transcribed into DNA upon infection & integrated into host genome
Genome type & examples of Group 7 viruses
- Double stranded DNA viruses with an RNA intermediate
- DNA genome but replicates through RNA intermediate
- Eg; HepB - dsDNA genome but produces an RNA intermediate during replication
Who discovered viruses
Martinus Beijerinck
What do all virions contain structurally (2)
- Viral genome -DNA/RNA never both
- Capsid - protective structural proteins
What are individual components of a capsid called
Capsomeres - arranged in repetitive pattern
what do some virions contain structurally (2)
- Envelope
- Attachment (spike) proteins - interact w cell surface receptors
What microscope is used to study viruses & why
Resolving power of an electron microscope is 1000 times better than light microscope (high resolution due to shorter wavelength of electrons compared to visible light)
Differences in SEM and TEM: sample prep
- SEM: fix, dehydrate, gold coat
- TEM: fix, dehydrate, resin embed, section, negative stain
Differences in SEM and TEM: Thickness
SEM: any thickness
TEM: must be thin
Differences in SEM and TEM: Field of view
SEM: large field of view
TEM: view of internal morphology (X-section)
Differences in SEM and TEM: resolution
- SEM: lower resolution
- TEM: higher resolution
How does Cryo-EM work
- version of EM that freezes many copies of sample into a glassy state
- hits them with an electron beam
- makes images into a high res 3D model of sample
How does Cryo-ET (electron tomography)
- tarfet area imaged at different angles by rotating microscope stage
- alignment of images at different angles -> gain 3D info of sample
The presence of what distinguishes viruses from viroids & prion
The presence of protein & nucleic acids
(viroids & prions have only RNA & protein)
2 types of viral symmetry
- Helical
- Icosahedral
(complex- T4 phage has icosahedral head & helical tail)
How many triangular faces does an icosahedral capsid have
20
How many subunits are needed to form a icosahedral capsid
Minimum 60 subunits needed
Why is icosahedral symmetry the most efficient arrangement of subunits in a closed shell
It requires the smallest no. of capsomeres to build the shell
What does the higher the T number mean in terms of viruses
The higher the T number;
* the more copies of capsid protein
* the more triangular facets per face
Why does the lipid envelope contain viral glycoproteins
- For attachment
- For masking from the immune system
What kind of coronavirus is SARS-CoV-2
Novel beta-coronavirus
positive-sense RNA virus
How many proteins does SARS-CoV-2 code for and what 4 of these are structural
- 29 total
- 4 structural (components of virion):
1. Spike (S) protein
2. Membrane (M) protein
3. Nucleocapsid (N) protein
4. Envelope (E) protein
SARS-CoV-2 cell entry mechanism
How does SARS-CoV-2 virus attach to host
The Spike (S) protein at the surface of virus particle is the virus attachment & fusion protein
SARS-CoV-2 cell entry mechanism
what cell receptor binds to the virion Spike protein
ACE-2 (angotensin converting enzyme)
SARS-CoV-2 cell entry mechanism
What cellular proteases aud in entry process & what do these do (2)
- TMPRSS2 (transmembrane serine protease 2) and Furin are the cellular proteases that aid in the entry process
- They function to:
1. Cleave S1 and S2 subunits
2. Activate the spike - triggers entry process
Omicron spike mutations & effects
- Omicron needs only ACE2 to get inside (not TMPRSS2 anf Furin)
- Cells w/o TMPRSS2 available for infection
- Variant encapsulated into endosome - drifts into cell & breaks out
