Virus 1st - 3rd lecture Flashcards
Timeline of discoveries
1884: Charles Chamberland (FR)
- Chamberland-Pasteur filter (also chickecholera)
1885: Louis Pasteur (FR)
- develops ? against rabies
- unable to find ? agent (“pathogen too small”)
1892: Dimitri Ivanosky (RUS)
- diseased tobacco plants
- filterable infectious agent? toxin?
(filtered water from that mixture - gave that to healthy plants but those healthy plants became sick
- he thought maybe its a “toxin” that passed through the filter and something that multiples inside cell so he didnt know it was a virus
- FIRST EVER VIRUS SEEN was tobacco mosaic disease)
1898: Martinus ? (NL)
- agent that only multiplies in cells
- contagium vivum fluidum
(virus; Latin: slimy liquid or poison)
1913: Wendell Stanley (USA)
- viral structure under ?
1898: Loeffler & Frosch (GER)
- ? proof of viral infections in animals
Timeline of discoveries which led to discovery of virus
1884: Charles Chamberland (FR)
- Chamberland-Pasteur filter
(also chickecholera?
- to stop cholera from passing through water)
1885: Louis Pasteur (FR)
- develops vaccines against rabies
- unable to find causative agent (“pathogen too small”)
(only knew “it” (virus) was really small and didn’t know what it was)
1892: Dimitri Ivanosky (RUS)
- diseased tobacco plants
- filterable infectious agent? toxin?
(filtered water from that mixture - gave that to healthy plants but those healthy plants became sick
- he thought maybe its a “toxin” that passed through the filter and something that multiples inside cell so he didnt know it was a virus
- FIRST EVER VIRUS SEEN was tobacco mosaic disease)
1898: Martinus Beijerinck (NL)
- agent that only multiplies in cells
- contagium vivum fluidum
(virus; Latin: slimy liquid or poison)
1913: “W”endell “S”tanley (USA)
- “v”iral “s”tructure under EM
1898: Loeffler & Frosch (GER)
- First proof of viral infections in animals
(they simply did again take blood from a deceased animal. This is an animal that had foot and mouth disease. So we worked with that virus and they filtered the blood through the Chamberland-Pasteur filter ?
They knew there’s no bacteria in there. Then they inject this in a healthy animal and they could mimic the disease again. So they knew something was in there and that something was a virus.
So this is where you can see the timeline of discoveries and the development of that filter that played a big role in getting to the basis of virology
So they knew something was in there and that something was a virus.
So this is where you can see the timeline of discoveries and the development of that filter that played a big role in getting to the basis of virology.)
Virus 100 nm (can’t see with light microscope, only with ELETRON MICROSCOPE can see viruses)
- virus are v small, 0.2 micrometer (bacteria same?)
General properties
§ ? and ? (filter pore size 0.2 μm)
§ Found in almost every ecosystem on earth
Obligate intracellular or extracellular? parasites (NEED another cell to survive)
§ ? outside host cells
§ Hijack and utilize host cellular metabolism to make ? or ?
§ Non-living entities (?!)
§ Surviving hours to ? outside host cells
§ Showing reduced infectivity with increased time inside or outside? host cells
§ Not having standard cellular ? (e.g. mitochondria, chloroplasts ribosomes, Golgi,…)
(they do show reduced infectivity but also after a period of time the virus, the longer the time outside of body more reduced infectivity (e.g. corona virus: taking distance, precautions -> virus more outside -> reduced infectvity)
Virus 100 nm (can’t see with light microscope, only with ELETRON MICROSCOPE can see viruses)
- virus are v small, 0.2 micrometer (bacteria same?)
General properties
§ small and filterable (filter pore size 0.2 μm)
§ Found in almost every ecosystem on earth
Obligate intracellular parasites (NEED another cell to survive)
§ inert outside host cells
§ Hijack and utilize host cellular metabolism to make energy or protein
§ Non-living entities (?!)
§ Surviving hours to days outside host cells
§ Showing reduced infectivity with increased time outside host cells
§ Not having standard cellular organelles (e.g. mitochondria, chloroplasts ribosomes, Golgi,…)
(they do show reduced infectivity but also after a period of time the virus, the longer the time outside of body more reduced infectivity (e.g. corona virus: taking distance, precautions -> virus more outside -> reduced infectvity)
(INERT: means that its not replicating outside host cells but still active and it can still infect u and start to replicate inside body)
General properties
§ Host range of viruses -> determined by virus requirements for attachment to ? cell
§ Vertebrates
§ Invertebrates
§ ?
§ Bacteria and Fungi
§ Many viruses though are ?-specific HOWEVER those that are zoonotic can change! (e.g. coronavirus, from animals to humans)
REMEMBER WHICH VIRUSES ARE ZOONOTIC!!!
General properties
§ Host range of viruses -> determined by virus requirements for attachment to host cell
§ Vertebrates
§ Invertebrates
§ protists
§ Bacteria and Fungi
§ Many viruses though are HOST-specific HOWEVER those that are zoonotic can change! (e.g. coronavirus, from animals to humans)
Giant viruses
§ Viruses whose viral particle magnitude, structure, genome length and complexity are ? than the standard virus families (> 300 kb genomes) e.g. ?, ?
Study of Veterinary Virology is important because …
- Viruses cause high rates of mortality and ? (condition of suffering from a disease) in animals
- Viral diseases in animals cause tremendous ? losses to livestock and poultry industries, and notional and global economy
- Some viruses are ? leading to disease outbreaks, epidemics and pandemics
- Animals can act as important ? for human disease
- The South Indian frog Hydrophylax bahuvistara. A peptide secreted from its skin fights the influenza virus. (Credit: Sanil George and Jessica Shartouny)
- knowing how these capsids move will help in the development of further treatments or interventions for HIV.
Giant viruses
§ Viruses whose viral particle magnitude, structure, genome length and complexity are larger than the standard virus families (> 300 kb genomes) e.g. mimivirus, medusavirus
Study of Veterinary Virology is important because …
- Viruses cause high rates of mortality and morbidity (condition of suffering from a disease) in animals
- Viral diseases in animals cause tremendous financial losses to livestock and poultry industries, and notional and global economy
- Some viruses are zoonotic leading to disease outbreaks, epidemics and pandemics
- Animals can act as important models for human disease
IMP SLIDE!
General virus structure
the smallest/easiest virus looks like the one in pic:
Bacteria have DNA
and viruses also only have DNA, TRUE OR FALSE?
Nucleocapsid contains ? (DNA and RNA) and ?
Envelope will help in protecting the genetic material, but would also assist in the viruses’s attachment to the ?
envelope spikes that can be very important in ? of viruses.
IMP SLIDE!
General virus structure
the smallest/easiest virus looks like this
Bacteria have DNA
and viruses also only have DNA, FALSE!
VIRUSES have both DNA and RNA
Nucleocapsid contains nucleic acid (DNA and RNA) and capsid.
Envelope of virus will help in protecting the genetic material, but would also assist in the viruses’s attachment to the cell.
envelope spikes that can be very important in mUTATION of viruses.
(The H1N1 that was mentioned before, H and N are actually spikes that change overtime and thats how influenza viruses can infect different host species and change over time. So this is the basis of your virus structure!)
IMP SLIDE!
General virus structure
§ VIRAL GENOME= viral ? or ?
CAPSID= protein shell that encases the viral ?
§ Most viruses have one capsid except ? (double layered capsid)
§ Exists in different ? (helical, icosahedral or complex)
§ Usually symmetrical or asymmetrical?
§ Function: ?, ? sites, attachment to ? cells
§ CAPSOMER= basic subunit protein of the ?
§ NUCLEOCAPSID= ? + viral ?
ENVELOPE= lipid bilayer with embedded (glycol)proteins
§ Facilitates virus entry to ?
§ Helps virus to adapt ? and evade host ? system
General virus structure
§ VIRAL GENOME= viral RNA or DNA
CAPSID= protein shell that encases the viral genome
§ Most viruses have one capsid except Reoviruses (double layered capsid)
§ Exists in different symmetries (helical, icosahedral or complex)
§ Usually symmetrical
§ Function: protection, antigenic sites, attachment to host cells
§ CAPSOMER= basic subunit protein of the capsid
§ NUCLEOCAPSID= capsid + viral genome
ENVELOPE= lipid bilayer with embedded (glycol)proteins
§ Facilitates virus entry to host cell
§ Helps virus to adapt fast and evade host immune system
General virus structure
§ VIRION= a complete virus particle that consists of an RNA or DNA core with a protein coat, sometimes with an ?, and that is the ? ? form of a virus
§ VIRUS= broad terminology used to describe any aspect of the infectious agent and includes: the infectious (?) or ? virus particle, or viral ? acid and ? in the infected host cell
§ VIROID= infectious particle largere or smaller? than any of the known viruses, an agent of certain plant diseases. The particle consists only of an extremely small shape? RNA or DNA? molecule, lacking the protein ? of a virus (still enough to cause disease and only affects plants)
General virus structure
§ VIRION= a complete virus particle that consists of an RNA or DNA core with a protein coat, sometimes with an envelope, and that is the extracellular infective form of a virus
§ VIRUS= broad terminology used to describe any aspect of the infectious agent and includes: the infectious (virion) or inacticated virus particle, or viral nucleic acid and protein in the infected host cell
§ VIROID= infectious particle smaller than any of the known viruses, an agent of certain plant diseases. The particle consists only of an extremely small circular RNA molecule, lacking the protein coat of a virus (still enough to cause disease and only affects plants)
diff. morphologies and genome to classify viruses and to attribute them to certain family
[PIC: General virus structure
look diff. but will always have genetic base code so the DNA, RNA and the protein code around that and potentially the envelope.
- bacteriophage (plays role in transduction, green thing is fimbriae of a bacteria and bacteriophage which is a virus attaches to it so it shows the difference between bacteria and virus)
- naked viruse (top center)
- Ebola: filamentous virus (bottom left); only virus ebola that looks like this!!
- the one in the bottom middle is rabies virus (more bullet-shaped)]
can’t use morphology to classify virus as one morphology is shared by more than one virus and can’t use EM not readily available in every lab, so there’s a “combination of different features of the virus structure and its genome” that we will use to classify viruses and to actually name viruses and to attribute them in a certain family -> use the ones on next slide to classify them
IMP slide!!
Classifying viruses
Envelope
- its parameters:
-> ?,
-> enveloped
Capsid symmetry
§ ?
§ ? (tobacco mosaic virus)
§ Complex
Nucleic acid
§ DNA
§ RNA
§ ? DNA & RNA (at different stages in life cycle)
Genome architecture:
§ Linear, circular, ?
§ Strandedness: single-stranded (ss), double
stranded (ds), ds with regions of ss
§ Sense: positive (+), negative (-), ? (+/-)
IMP
Classifying viruses
Envelope
- its parameters:
-> naked,
-> enveloped
Capsid symmetry
§ icosahedral
§ helical (tobacco mosaic virus)
§ Complex
Nucleic acid
§ DNA
§ RNA
§ BOTH DNA & RNA (at different stages in life cycle)
Genome architecture:
§ Linear, circular, segmented
§ Strandedness: single-stranded (ss), double
stranded (ds), ds with regions of ss
§ Sense: positive (+), negative (-), ? (+/-)
Classifying viruses: envelope
§ An envelope is the ? membrane of a virus, an extra ? surrounding the protein ?
can spikes be present on naked capsid viruses?
Classifying viruses: capsid symmetry
- capsid is that protein coat which can be either
1. ?
2. ?
3. ?
Capsomeres and nucleic acid are wound together and form a ? or ? tube
In animal viruses: helical nucleocapsids are always enclosed within a ? ? (so it never exists as a naked virus, but will always have an envelope)
In plat viruses: ? helical nucleocapsids are common
Classifying viruses: envelope
§ An envelope is the outer membrane of a virus, an extra lipid bilayer surrounding the protein capsid
can spikes be present on naked capsid viruses? YES!
Classifying viruses: capsid symmetry (pic)
- capsid is that protein coat which can be either
1. icosahedral
2. complex
3. helical
Capsomeres and nucleic acid are wound together and form a helical or spiral tube
In animal viruses: helical nucleocapsids are always enclosed within a lipoprotein envelope (so it never exists as a naked virus, but will always have an envelope)
In plat viruses: naked helical nucleocapsids are common
1st and 2nd one in pic is tobacco mosaic virus (helical)
green thing, 3rd pic in pic -> animal virus helical nucleocapsid surrounded by envelope
Another capsid symmetry is
PROTOMERES: aggregate to form capsomers which are either ? or ?
5 together -> penton
6 together -> hexon
either hexons or pentons (in pic too!)
Classifying viruses: capsid symmetry
§ Virions are composed of ? parts, each with ? ? and shapes
§ Bacteriophage: shape? head and shape? tail
(have more than just their genome, and have different membranes and have inner and outer membranes and spikes around it (complex capsid symmetry)
pox virus: ? symmetry
- VERY LARGE (? ANIMAL virus that u need tp consider) virus
- pox virus cause pox
(pox virus are around 200 nm and other small viruses ~20nm)
Classifying viruses: capsid symmetry
§ Virions are composed of several parts, each with separate symmetries and shapes
§ Bacteriophage: icosahedral head and helical tail
(have more than just their genome, and have different membranes and have inner and outer membranes and spikes around it (complex capsid symmetry)
pox virus: complex symmetry
- VERY LARGE (largest ANIMAL virus that u need tp consider) virus
- pox virus causes pox
Classifying viruses: nucleic acid
DNA viruses:
§ Very stable or unstable?
§ Usually single or double helix?
§ Accurate ?
§ Larger or Smaller? genomes
RNA viruses:
§ More or less stable?
§ Mixture of ? and ?
§ ?-prone replication
Classifying viruses: nucleic acid
DNA viruses:
§ Very stable
§ Usually double helix
§ Accurate replciation
§ Larger genomes
do they mutate over time? - NO as they are stable thus can develop vaccines as same proteins expressed.
RNA viruses:
§ less stable
§ Mixture of ss and ds
§ error-prone replication
- multiple changes of mutation so diff. proteins expressed e.g. corona (rna) virus, influenza (diff. influenza every year..)
Classifying viruses: genome architecture
§ Reflection of different ? strategies
§ Strandedness: double-stranded (ds) or single-stranded (ss)
§ Sense: polarity of the genome, in relation to ? (5’-3’)
§ POSITIVE sense: geneticl material has same or diff. polarity as viral mRNA? -> need or no need for transcription?, direct translation into proteins
§ NEGATIVE sense: genetic material is complementary or same as the mRNA? -> transcription before translation
Classifying viruses: genome architecture
§ Reflection of different replication strategies
§ Strandedness: double-stranded (ds) or single-stranded (ss)
§ Sense: polarity of the genome, in relation to mRNA (5’-3’)
§ POSITIVE sense: genetic material has same polarity as viral mRNA? -> no need for transcription, direct translation into proteins
§ NEGATIVE sense: genetic material is complimentary as the mRNA? -> transcription before translation
(ss POSITIVE RNA viral genome
Remember, the positive sense is the same direction as messenger RNA. So it functions as a messenger RNA, so the ribosomes can directly translate that viral genome.
So the moment that the ribosomes see that viral genome in the cell, they can start to translate it into viral proteins.
The other enzyme that’s very important is an RNA-dependent RNA polymerase that will allow you to switch from negative-sense RNA to positive-sense RNA and backward.
And so it’s the same enzyme that can switch between negative and positive sense RNA,
That RNA-dependent RNA polymerase is an enzyme that we do not have.
So it’s something that needs to be encoded by the viral genome. THEREFORE THE VIRUSES NEED THAT ENZYME (viral protein - orange one on slide
NEGATIVE RNA viral genome
So you need first a transcription step ( as its (-) so it isn’t same as the mRNA and ribosomes can’t read it yet)with the RNA-dependent RNA polymerase to the messenger,
RNA to the positive sense, and then you will have the translation steps up here.
Then Negative RNA viral genome is transcribed first to the messenger RNA
then the ribosomes can translate to viral proteins.
this pathway in which we will have continuous copying of our viral genome in order to have a replication here of our viral genome (the last steps in the bottom right (negative RNA) - THUS + RNA much faster!
reverse transcriptase helps RNA go backwards to DNA
-> the ssRNA and ssDNA (both +) under reverse transcribing viruses first have to make double-stranded intermediate and then go to mRNA
-> ssRNA - does not make double-stranded DNA as it is complimentary to the mRNA
CHAIN OF INFECTION
- They can be released from reservoirs two different ways and transmitted into susceptible host species.
- reservoirs can be animals, and humans, so reservoirs at a population level
Addendum: COVID-19 pandemic
- It had some passages in an intermediate host, and while doing so, the virus changed and at one point it could infect human cell.
- More specifically, a human lung cell. And at that point it was adapted to replicate in the human population.
- easy to get in contact w a reservoir of virus? YES! as travelling to other parts of the world is easier now and now living in wild animals’ territories as well
- So you will be potentially be a carrier for, let’s say, and crossover of viruses from one population to another.
R
So you can see all the different influenza viruses and types and how they can circulate either within one population but also across the species and even between wild and captive animals.
So our approach to certain diseases requires a one-health approach.
Endocytosis
§ Process in which the virus gains entry into the host cell without passing through the cell ?
§ Active transport in which the virus is engulfed by an ?-using process
NOTE: it’s really the host cell that reacts to that attachment (the virus doesn’t make. a hole in the PM or anything) and that takes up and goes over virus.
ENVELOPED VIRUS
1. Virus’s envelope spikes bind to receptors enriched in the membrane of a coated pit
- Binding to the receptor triggers * ?-mediated ? *
- Increased acidity allows nucleocapsid to escape from the ?
NAKED VIRUS
1. virus’s capsid proteins bind to ? and trigger receptor-mediated endocytosis
- nucleic acid is extruded from ? into cytoplasm
Endocytosis
§ Process in which the virus gains entry into the host cell without passing through the cell membrane
§ Active transport in which the virus is engulfed by an energy-using process
NOTE: it’s really the host cell that reacts to that attachment (the virus doesn’t make. a hole in the PM or anything) and that takes up and goes over virus.
ENVELOPED VIRUS
1. Virus’s envelope spikes bind to receptors enriched in the membrane of a coated pit
- Binding to the receptor triggers * receptor-mediated endocytosis *
- Increased acidity allows nucleocapsid to escape from the endosome
NAKED VIRUS
1. virus’s capsid proteins bind to receptor and trigger receptor-mediated endocytosis
- nucleic acid is extruded from endosome into cytoplasm
(Remember, they want to get to that genetic material. All the rest is rubbish
The sooner they can get rid of their envelope and their capsid, the better.)
Adenovirus causes ?
So here you can see the attachment as a result here, the formation of that vesicle and that and also that is present inside our cytoplasm.
Adenovirus causes common cough
Membrane fusion
§ Process of merging (fusion) of the virus ? with the host cell lipid bilayer membrane (capsid can’t fuse with PM as capsid made of proteins)
§ Mediated by ?-independent fusion proteins (e.g. HIV, measles) or ?-dependent fusion proteins (e.g.
Influenza virus) that are anchored on the virus ?
§ Only for * ? viruses!
Membrane fusion
§ Process of merging (fusion) of the virus envelop with the host cell lipid bilayer membrane
§ Mediated by pH independent fusion proteins (e.g. HIV, measles) or pH dependent fusion proteins (e.g.
Influenza virus) that are anchored on the virus surface
§ Only for enveloped viruses!
BOTTOM IMAGE
And in the beginning, if you can see this on this electron image, the cell wall or cell membranes or maybe cell wall, cell membrane is thick, it’s because it fuzes with that envelope, it’s going to be thick, but at the end, it will restore again.
These are all bacteriophages. And this is one bacterial Escherichia coli.
One bacterium. It’s attacked by many, many different bacteriophages.
And you can see that some of those have been able to already inject the genetic material inside.
These are empty. The empty capsids are lighter (present on their membrane) Yeah, the darker colored here are our newly formed viruses with, again, genetic material.
The dark things present near the E coli’s membrane are the bacteriophages that haven’t yet injected their genetic material inside their bacterium
Step 4: Replication/Synthesis (this slide only above pic)
(Recall “central dogma” transcription, translation and the flow of it)
= the genomic expression of the viruses, using ? cellular machinery to replicate and make functional and structural proteins
§ Different replication strategies depending on genome ? of the virus (cfr. Baltimore classification)
(With these different replication strategies depending on the genome architecture, we have that Baltimore classification so this is comparable to the table that I showed you before. So all of these seven need to go to messenger RNA from which our proteins are built.)
Step 4: Replication/Synthesis (this slide only above pic)
(Recall “central dogma” transcription, translation and the flow of it)
= the genomic expression of the viruses, using host cellular machinery to replicate and make functional and structural proteins
§ Different replication strategies depending on genome architecture of the virus (cfr. Baltimore classification)
IMP SLIDE!!
If we look at the key enzymes that will play a role in that replication or synthesis step, then we have our DNA polymerase that is required for the DNA replication.
We have our RNA polymerase and then we have. here the ribosome enzymes.
And so DNA polymerase, RNA polymerase and the ribosome enzymes for the translation, these are present. Viruses don’t need to generate those. They’re alr present in the cell.
They’ll just use the enzymes from the cell but What are the ones they do need to generate the reverse transcriptase?
It’s only generated by this special group of viruses, reverse transcriptase viruses and the RNA-dependent RNA polymerase.
They need to generate as well to go from a positive sense to a negative sense and back.
When we look at this replication, the viruses will replicate in a very precise order. They will not first make capsid proteins. That’s irrelevant.
The first thing they want to make are these enzymes they might be missing. So first they will make sure that they make RNA-dependent RNA polymerase or they make a reverse transcriptase. Then they will start to generate copies of the genetic material.
Then the building blocks, the proteins. And once they have all of these, maybe some spikes and also goes in a very precise order. Now, when they are doing that, they are controlling the metabolism in the cell.
They are controlling the replication strategy. It’s genius how just that piece of viral genetic material can control this one cell.
BUDDING
4th one: With some enzymes, they’ll with a scissor like enzyme help, they’ll squeeze of the bud and you’ll have your free infectious variant.
budding is something we see with alphaviruses. The buds pink circle that is protruding outwards is called virion. Also, HIV is a virus that is released through budding.
BOTTOM RIGHT PIC: So here you can find the budding of a virus from the surface of a white blood cell. It has infected this white blood cell. It assembles its material next to the cell membrane, and it is released here.
It’s logical that budding is for an envelope virus because as you can see, the envelope is actually part of that cell membrane and its the same composition as the phospholipid bilayer that is being formed around your capsid and your genetic material.
Exocytosis: a process by which the virions they pass through these different organelles, they will get potentially an envelope. Sometimes they lose the envelope again. So there’s a different steps in here, but they just pass through these organelles and are released.
TYPE 2: life cycle of RNA viruses
- So a ? single-stranded RNA virus can immediately be translated.
- Ribosomal enzymes will recognize that can immediately lead to protein production (as its ? so it isn’t complimentary and same as the mRNA)
- Some of these proteins will be essential enzymes such as ?-dependent RNA ? -> the first one being produced.
- The RNA-dependent RNA polymerase plays a role in switching from positive sense to ?-sense RNA (- is complimentary to mRNA)
- So because of the presence of polymerase, you can generate the complementary strand from a positive strength or the opposite way around from a negative single strand to a positive single strand.
- This is your replication cycle for a positive single-strand RNA virus and for a negative single-strand RNA virus, you first need that ? step as u need to generate an mRNA
- All of it happening in the ? -> Type #? Lifecycles.
TYPE 2: life cycle of RNA viruses
- So a positive single-stranded RNA virus can immediately be translated.
- Ribosomal enzymes will recognize that can immediately lead to protein production (as its + so it isn’t complimentary and same as the mRNA)
- Some of these proteins will be essential enzymes such as RNA-dependent RNA polymerase -> the first one being produced.
- The RNA-dependent RNA polymerase plays a role in switching from positive sense to negative-sense RNA (complimentary to mRNA so needs to be transcription)
- So because of the presence of that polymerase, you can generate the complementary strand from a positive strength or the opposite way around from a negative single strand to a positive single strand.
- This is your replication cycle for a positive single-strand RNA virus and for a negative single-strand RNA virus, you first need that transcription step as u need to generate an mRNA
- All of it happening in the cytoplasm! Type two Lifecycles.
1st Exception to RNA virus: life cycle of influenza viruses
- in pic can see diff. lines
- The genome is not just one line, but this actually a ? of genome.
- In fact, an influenza virus has #? segments.
- It has a segment, the genome. It’s the only virus family we will study that has a SEGMENT, the genome.
- Because of that, they will have a difference in the ? cycle, although they are RNA viruses they replicate inside the ? unlike other RNA virus that replicate in cytoplasm.
- *** IMP! So if I show you an image of a virus with a segment, the genome replicating in the nucleus on the exam,
- the answer should be this is the replication cycle of influenza viruses!!
1st Exception to RNA virus: life cycle of influenza viruses
- in pic can see diff. lines
- The genome is not just one line, but this actually a segment of genome.
- In fact, an influenza virus has eight segments.
- It has a segment, the genome. It’s the only virus family we will study that has a SEGMENT, the genome.
- Because of that, they will have a difference in the replication cycle, although they are RNA viruses they replicate inside the NUCLEUS unlike other RNA virus that replicated in cytoplasm.
- *** So if I show you an image of a virus with a segment, the genome replicating in the nucleus on the exam,
- the answer should be this is the replication cycle of influenza viruses!!
2nd Exception to RNA viruses: life cycle of retroviruses
- characterizing these retroviruses is the presence of a very special enzyme, the REVERSE TRANSCRIPTASE.
- So these are RNA viruses, but the first step they will do is go in the opposite direction in your transcription translation process.
- So they have RNA and with the reverse transcriptase, they will generate DNA in the opposite direction as what we normally see in molecular biology.
- So the first thing they do is generate a ? (pink in pic)
- And then they will bring this viral DNA into the ?. (So that’s an RNA virus still going with its genetic material into the nucleus.)
- Moreover, they will incorporate that piece of DNA into the host cell ? (They literally could open the host cell genome and squeeze in)
- Now there’s a piece of viral genome inside the host genome. Now, that piece we call a “ ? “. this ? may divide indefinitely with the host cell ?.
(so logical to first reverse transcribe as they can’t paste RNA single strand into a double strand, the genome,
need double stranded DNA to match it in there. And that’s why they have that reverse transcriptase.)
ADVANTAGE OF THIS TACTIC: It’s passed on to the ? cells!
- So these are RNA viruses, but the first step they will do is go in the opposite direction in your transcription translation process.
- So they have RNA and with the reverse transcriptase, they will generate DNA in the opposite direction as what we normally see in molecular biology.
- So the first thing they do is generate a double stranded DNA (pink in pic)
- And then they will bring this viral DNA into the nucleus. (So that’s an RNA virus still going with its genetic material into the nucleus.)
- Moreover, they will incorporate that piece of DNA into the host cell genome (They literally could open the host cell genome and squeeze in)
- Now there’s a piece of viral genome inside the host genome. Now, that piece we call a “ provirus”. this pro virus may divide indefinitely with the host cell DNA.
(so logical to first reverse transcribe as they can’t paste RNA single strand into a double strand, the genome,
need double stranded DNA to match it in there. And that’s why they have that reverse transcriptase.)
ADVANTAGE OF THIS TACTIC: It’s passed on to the daughter cells!
This is a strategy that indeed immunosuppressive viruses used to cause these extensive lung diseases. And that’s why you can’t always get rid of an immunosuppressive disease because it’s encoded in the genome.
