WEEK 3: MOLECULAR VIROLOGY AND INFECTION Flashcards
Are viruses ABSOLUTELY DEPENDENT on at least some cellular factors and on cellular metabolic energy?
- YES!
What general terms are viruses known as?
- Obligate intracellular parasites
What are the two phases in a viruses life cycle?
- A VIRION
2. INFECTED CELL
What are virions?
- A SINGLE infectious particle –> what we think of when we say viruses
What are virions inert carriers of ?
- Nucleic acid payload
Which phase of the life cycle do virions participate in?
- The extracellular phase which is a spore
Can virions perform replication or metabolism alone?
- NO!
What process do viruses regulate?
- C, N and P fixation (global cycles)
- They ‘drive’ global cycles
Can a latent virus become active again at another time?
- YES!
Is the virome a major part of the microbiome?
- YES!
Are the vast majority of DNA sequences in human blood viral?
- YES!
- Viral sequences present in ALL tissues
Do ALL viruses make you sick?
- NO
What are 3 examples of q’good’ viruses?
- Polydnaviruses –> Survival of wasp egg in insect host
- Retroviruses –> mammals–> evolution of placenta
- Parvoviruses–> aphids–> needed for development of WINGS
What are 4 viruses that are useful for us?
- Oncolytic virotherapy
- Viral gene therapy
- Reverse transcriptase
- Phage therapy
What does Oncolytic virotherapy involve?
- Viruses with propensity to target/replicate within tumour cells –> Parvivirus
What does viral gene therapy involve?
- Gene therapy using an adenovirus vector
What does reverse transcriptase do and how is it useful?
- Revolutionised molecular biology
- Can generate cDNA from RNA –> useful for PCR, cloning, Sequencing, genomics
What does Phage therapy involve?
- Targeting bacterial diseases and destroying them
e. g. Destruction of MDR bacteria
What are the ‘Historic’ (not used anymore) properties that can classify a microbe as a virus?
- Very small
- But now there are giant viruses so we don’t use it anymore
Do viruses grow when placed in broth?
- NO! THEY DO NOT GROW!!
What is the eclipse period defined as?
- NO new virus present in host cells (immediately when injected, there will be a period of ‘nothing’ happening)
What is the burst size defined as?
- Large number of new viruses produced per infected cell
“Viruses do not grow and divide like bacteria, but are _________, assembled from _____________ and released.”
“Viruses do not grow and divide like bacteria, but are MOLECULAR NANOMACHINES assembled from PREBUILD NEWLY SYNTHESIZED COMPONENTS and released.”
What happens when an extracellular inert particle enters the cell?
- Components dissociate
- Eclipse phase occurs –> NO VIRION detectable
- After some time, protein components made, genome is REPLICATED
- Virions SELF ASSEMBLE from newly synthesized components
Which two components are ALL virions comprised of ?
- Nucleic acid and protein
Can virions have BOTH DNA and RNA?
- NO
- They have to have ONE or the OTHER
What is a nucleocapsid made up of?
- Capsid + nucleid acid
What are many identical units of nucleocapsids called? -
- capsomeres
What is a virion that only has a nuceloplasmid called?
- A naked virus
What is a virion that has a membranous lipid called?
- Enveloped virus
Where will the viral spike/coat proteins that bind to host cell/tissue receptors be found if the virus is NAKED?
-Part of the capsid OR a protein coming off from the capsid
Where will the viral spike/coat proteins that bind to host cell/tissue receptors be found if the virus is ENVELOPED?
-Glycoproteins (bc. inside the envelope)
What are 3 things that the host cell receptors do when binding?
- Recognition of host cell
- Cell entry
- Penetration/uncoating (Destabilisation)
What is the general order from inside to outside of a virion?
- Nucleic acid (DNA or RNA)
- Protein shell /Capsid
- Other layers (Matrix–> HIV) (not always)
- Envelope with glycoprotein (not always)
What is the PRIMARY DEFINING feature of a virus?
- Whether there is an envelope present or not
Apart from the main defining feature of a virus being the envelope, what are the 3 main structures of viruses?
- Spherical
- Helical
- Complex
What are the details of a SPHERICAL virus?
Icosahedral ORDERED SYMMETRY
- Formed from REPEATING UNITS of protein
- Regular polyhedron with 20 TRIANGULAR FACES
What are the details of a HELICAL virus?
Rod shaped coat
- Multiple REPEATING copies of protein coated ONTO GENOME
- Hollow tube–> “spherical staircase”
What are the details of a COMPLEX virus?
Large viruses and a MIXTURE of shapes with NO CONSISTENT SYMMETRY
-Poxyviruses/giant viruses, many bacteriophages, archeal viruses
What predictions can we make from just knowing the structure of a virus?
- Cell entry
- Disassembly, release of genome
- Assembly of virion
- Egress (leaving)
- About stability/transmission Enveloped= usually less environmentally stable
- Naked= More stable and RESISTANT
What do viruses lack the genetic information to encode?
- Machinery….
o To generate metabolic energy, C metabolism
o To generate membranes
o For protein synthesis
Without cells, what are viruses?
- Inanimate, complex organic matter
How are progeny (virions) formed?
-By SELF-ASSEMBLY from newly synthesied components within host cell
Do virions grow and divide?
- NOONONOOO
Do all viruses (even giant viruses) lack a COMPLETE protein synthesis (ribosome) machinery?
- Yes!
Do all viruses have to be able to make mRNA which is translated by host cell ribosomes?
- YES!
What are the 5 basic steps of repliciation of a virus ?
- ATTACHEMNT
- PENETRATION/UNCOATING
- GENE EXPRESSION/REPLICATION
- ASSEMBLY
- RELEASE