Replication cycle of influenza A Virus. 1 Attachment of influenza virus to sialic acid receptors on the cell surface. 2 Penetration of the virus into the cell through receptor mediated endocytosis. 3 Fusion of viral envelope with endosome membrane. 4 Uncoating and exit of the genome
Genome
In modern molecular biology and genetics, the genome is the genetic material of an organism. It consists of DNA (or RNA in RNA viruses). The genome includes both the genes and the non-coding sequences of the DNA/RNA.
How does influenza viruses replicate?
The replication of the influenza genome involves two steps: transcription of complimentary RNA (cRNA), followed by transcription of new vRNA copies using the cRNAs as templates.
What is the replication process of a virus?
In general terms, virus replication involves three broad stages which are present in all viruses: initiation of infection, replication and expression of the genome, and the release of mature virions from the infected cell.
What enzyme does the influenza virus use for replication?
RNA-dependent RNA polymeraseThe enzyme that reproduces influenza RNA is known as an RNA-dependent RNA polymerase. This enzyme, which consists of the viral proteins PA, PB1, and PB2, is present in every virus particle.
What is the influenza replication cycle?
The influenza virus life cycle can be divided into the following stages: entry into the host cell; entry of vRNPs into the nucleus; transcription and replication of the viral genome; export of the vRNPs from the nucleus; and assembly and budding at the host cell plasma membrane.
What are the 5 steps of virus replication?
Most productive viral infections follow similar steps in the virus replication cycle: attachment, penetration, uncoating, replication, assembly, and release.
What are the 7 steps of viral replication?
As discussed above, they are carried out in a series of 7 steps that is: attachment, penetration and entry, uncoating, replication, synthesis of virus components, assembly of virions and lastly the release of virions.
How does influenza grow?
During the incubation period, the virus replicates in the cells that make up the chorioallantoic membrane. As new virus particles are produced by budding, they are released into the allantoic fluid. To harvest the virus, the top of the egg shell – the part covering the air sac – is removed.
How does influenza get into the cell?
The influenza virus enters the host cell by having its hemagglutinin bind to the sialic acid found on glycoproteins or glycolipid receptors of the host. The cell then endocytoses the virus. In the acidic environment of the endosomes, the virus changes shape and fuses its envelope with the endosomal membrane.
What cells does the influenza virus infect?
Influenza virus infects respiratory epithelial cells that line the upper (including nasal) through lower (to the alveoli) respiratory tract. A key parameter in determining the extent of associated disease is the degree to which the lower respiratory tract becomes invaded by the virus [7].
Does influenza have DNA or RNA?
RNAAll influenza viruses consist of single-stranded RNA as opposed to dual-stranded DNA. The RNA genes of influenza viruses are made up of chains of nucleotides that are bonded together and coded by the letters A, C, G and U, which stand for adenine, cytosine, guanine, and uracil, respectively.
During which of the following steps in viral replication of influenza does a virus acquire its envelope?
Enveloped viruses, such as influenza A virus, are typically released from the host cell by budding. It is this process that results in the acquisition of the viral phospholipid envelope.
What cycle of replication is used by the common cold virus?
There are two processes used by viruses to replicate: the lytic cycle and lysogenic cycle.
What is the first step of viral replication?
AttachmentAttachment. It is the first step of viral replication. The virus attaches to the cell membrane of the host cell. It then injects its DNA or RNA into the host to initiate infection.
How does a virus replicate quizlet?
Where and how do DNA viruses replicate? DNA viruses replicate in the nucleus, using host DNA-dependent RNA polymerase to make mRNA, then DNA dependent DNA polymerase to make DNA (either from virus or host).
How do virus replicate a level biology?
Viruses replicate by injecting their nucleic acid into a host cell: First, a virus uses attachment proteins on its surface to bind to complementary receptor proteins on the surface of a host cell. The virus then injects its DNA or RNA into the host cell.
How do mRNA viruses replicate?
To facilitate RNA replication, (+)RNA viruses interact with numerous host molecules through protein–protein, RNA–protein and protein–lipid interactions. These interactions lead to the formation of viral replication complexes, which produce new viral RNA progeny in host cells.
How is vRNA replicated?
Initially the full-length complementary copy of the vRNA (cRNA) is formed, which is then copied to generate vRNA. Unlike the initiation of viral mRNA synthesis, the production of cRNAs and vRNAs does not require a primer.
How does acidification affect the cytoplasm?
Acidification of the viral core helps in the release of the viral RNPs from the endosome into the cytoplasm. The exposure of the virus to acidic pH within the lumen of the endosome, and subsequent protons flow into the viral interior, weakens the interaction of the M1 protein layer with the viral envelope and the RNPs.
What is the role of a rdrp in a cell?
The influenza virus RdRp, a heterotrimer composed of three subunits, PA, PB1 and PB2, is required for the synthesis of capped, polyadenylated mRNAs during transcription as well as full-length complementary RNA (cRNA) and genomic RNA (vRNA) in the cell nucleus during replication, using the vRNAs as template.
What is the cap of a cellular messenger RNA?
Mature cellular messenger RNAs (mRNAs) have a 5 ′ methylated cap and a poly A tail. The vRNPs have poly A tails but no 5 ′ caps and the viral mRNAs have a 5 ′ methylated cap and a poly A tail, but the vRNA do not contain 5 ′ cap (Plotch et al. 1978 ).
Which enzyme produces abortive short RNA chains?
The viral RdRp enzyme produces predominantly abortive short RNA chains in the absence of influenza virus replication factor 1 (IREF-1)/minichromosome maintenance (MCM), and not the full-sized cRNA.
Where are mRNAs transported?
The newly synthesised mRNAs are transported back from the nucleus into the cell cytosol for translation into proteins. The transmembrane proteins (HA, NA and M2) production begins in the cytosol. Simultaneously, glycosylation and folding of these newly forming polypeptide chains occurs in the endoplasmic reticulum. These proteins are further modified and then carried through the Golgi apparatus and the trans-Golgi network to the cell’s plasma membrane (Doms et al. 1993 ).
Does RNA replication increase transcription?
The RNA replication efficiency, but not transcription, can be increased by stabilization of cRNA due to modified interactions of monoubiquitinated NP with RNA. Further, the functions of RNP complex during RNA replication can be influenced by the interactions of cellular deubiquitinase USP11 with PB2, PA and NP.
How many proteins does the influenza virus have?
Given that the influenza A virus only encodes for 11 proteins, it has generated many sophisticated methods of utilizing the host cell’s machinery for its own purposes. Through understanding viral transcription, we have learned of a unique mechanism whereby the virus hijacks the host’s transcription machinery for its own benefits.
Which methyl group is the primer for influenza virus RNA transcription?
Bouloy M, Plotch SJ, Krug RM. Both the 7-methyl and the 2'-O-methyl groups in the cap of mRNA strongly influence its ability to act as primer for influenza virus RNA transcription. Proc Natl Acad Sci USA. 1980;77(7):3952–3956. [PMC free article][PubMed] [Google Scholar]
What is the family of influenza A?
Influenza A belongs to the family of Orthomyxoviridae. It is an enveloped virus with a genome made up of negative sense, single-stranded, segmented RNA. The Influenza A viruses have eight segments that encode for the 11 viral genes: hemagglutinin (HA), neuraminidase (NA), matrix 1 (M1), matrix 2 (M2), nucleoprotein (NP), ...
What are the three proteins in the viral envelope?
The viral envelope is made up of a lipid bilayer that contains three of the viral transmembrane proteins: HA, NA, and M2.
How many genes does a virus have?
It is an enveloped virus with a negative sense RNA segmented genome that encodes for 11 viral genes. This virus has evolved a number of mechanisms that enable it to invade host cells and subvert the host cell machinery for its own purpose, that is, for the sole production of more virus. Two of the mechanisms that the virus uses are “cap-snatching” ...
Where do viruses bud?
Virus particles bud from the apical side of polarized cells [4]. Because of this, HA, NA, and M2 are transported to the apical plasma membrane. It has been shown through deletion and mutational analysis that the tail of M2 is extremely important in the formation of viral particles. Viruses that had the M2 tail deleted or partially mutated produced elongated particles [49]. M1, which is present underneath the lipid bilayer, is important in the final step of closing and budding off of the viral particle [6,50]. Several host factors are involved in the budding off of viruses from plasma membranes, and these are reviewed in [4,51].
Does replication require a primer?
Replication of the genome does not require a primer; instead, the viral RNA dependent RNA polymerase (RdRp) initiates RNA synthesis internally on viral RNA. This is possible, as the extreme 5’ and 3’ ends of the genome exhibit partial inverse complementarity and, hence, are able to base pair with one another to form various corkscrew configurations. It appears that a great number of di-nucleotide base pairs form, although the full mechanism of viral genome replication is still yet to be understood [13-16].
How does the virus enter the host cell?
Influenza virion enters inside the host cell by the process of endocytosis. There in the cytoplasm the nucleocapsid separates from the envelop and moves into the nucleus wherein the viral genome replication takes place. Un-coating results in activation of the virus RNA polymerase.
How big is the influenza virus?
Morphology of Influenza Virus: Influenza virus (Fig. 14.18) is pleomorphic and its diameter is 80- 120 nm. It is an enveloped virus possessing genome segmented into eight linear single- stranded molecules ranging in size from 890 to 2341 nucleotides.
How many proteins are in the viral genome?
Ten virus proteins are encoded by the eight segments of viral genome. Some of these proteins are involved in viral genome replication while others are structural proteins used in assembly of virion. Details of assembly of virions are still not known with certainty.
Which enzyme breaks down the sialic acid component of the cytoplasmic membrane?
However, neuraminidase spike is an enzyme which breaks down the sialic acid component of the cytoplasmic membrane. On the inner side of the envelop there is M-protein which provides rigidness and thus stabilizes the lipid bilayer.
Where are mRNA molecules transcribed?
The mRNA molecules are then transcribed from the virus RNA inside the nucleus using oligonucleotide primers and they move to the cytoplasm. ADVERTISEMENTS: However, the virus proteins are synthesized in the cytoplasm. Ten virus proteins are encoded by the eight segments of viral genome.
Where do viruses replicate?
Influenza viruses replicate within the nucleus of the host cell. This uncommon RNA virus trait provides influenza with the advantage of access to the nuclear machinery during replication. However, it also increases the complexity of the intracellular trafficking that is required for the viral components to establish a productive infection.
How does vrNP enter the nucleus?
( 76 )]. Supported by numerous studies, the current model is that the newly released cytoplasmic vRNPs use the importin- α–importin- β nuclear import pathway to gain entry to the host cell nucleoplasm (Figure 2 B, steps vi and vii) ( 77 – 83 ). To initially engage this pathway, it is thought that the vRNPs use the surface exposed nuclear localization sequences from the numerous NP molecules to recruit the adapter protein importin-α ( 80 – 82 ). Upon binding to the vRNP, importin-α is recognized by the importin-β transport receptor, which directs the vRNP to the nuclear pore complex, where it is transported into the nucleoplasm.
What is the difference between a type A and type B influenza virus?
Influenza viruses belong to the Orthomyxoviridae family and are classified as either type A, B, C, or the recently identified type D ( 1, 2 ). Influenza A viruses (IAVs) and type B viruses (IBVs) contain 8, negative-sense, single-stranded viral RNA (vRNA) gene segments (Figur e 1 A) ( 3, 4 ), which encode transcripts for 10 essential viral proteins, as well as several strain-dependent accessory proteins (Figure 1 B). In comparison, influenza type C and D viruses only possess seven vRNA gene segments, as the hemagglutinin–esterase fusion protein vRNA replaces the hemagglutinin (HA or H) and the neuraminidase (NA or N) vRNAs ( 1, 2 ). IAVs will be the main focus of this review since they are the primary agents responsible for influenza pandemics, and a major contributor to the annual influenza epidemics in the human population ( 5 ).
What are the UTRs of influenza A and B?
Influenza A and B viruses. (A) Schematic of the eight viral RNA (vRNA) gene segments that comprise the influenza A and B genomes. The 5′ and 3′ untranslated regions (UTRs), which contain the viral promoters, are represented with a line, and the box corresponds to the coding region within each vRNA.
How does HA fusion work?
Fusion of the viral-endosomal membranes by HA occurs through multiple steps [reviewed in Refs. ( 72, 73 ), and requires cleavage of HA by host cell proteases into two subunits, HA1 and HA2 ( 55, 74, 75 )]. The cleavage (see HA Proteolytic Activation at the Golgi or Plasma Membrane) is required to enable the exposure of the fusion peptide on the N-terminus of the HA2 upon the pH change in the endosome ( 69 ). Once exposed, the fusion peptide inserts into the endosomal membrane, while the C-terminal transmembrane domain (TMD) anchors HA2 in the viral membrane, creating a pre-hairpin conformation (see Figure 2 B, step ii “box”). The HA2 trimers then fold back on themselves creating a hairpin that begins to position the two membranes in close proximity to each other (see Figure 2 B, step iii “box”). The hairpin bundles then further collapse into a six-helix bundle, and in doing so, the two membranes come closer together enabling the formation of the lipid stalk, and the subsequent fusion of the two membranes (Figure 2 B, step iv). To date, not all of these stages have been observed with HA and some have been inferred based on observations of related fusogens from other viruses.
What happens during the replication cycle of a virus?
During the replication cycle of the virus, a "switch" from mRNA to cRNA synthesis occurs, but the mechanism by which this switch occurs remains unclear. The viral nucleoprotein and its interaction with the polymerase proteins and vRNA might play a role in this process.
Where is vRNA transcribed?
During the replication cycle of the virus, the genomic vRNA is transcribed into positive-strand mRNA and complementary RNA (cRNA) in the cell nucleus. The promoter for the synthesis of mRNA molecules is l …. The genome of influenza A virus consists of eight segments of negative-strand viral RNA (vRNA). During the replication cycle of the virus, the ...
Where do viral proteins stay after a virus is released?
After virion release some viral proteins remain within the host’s cell membrane, which acts as potential targets for circulating antibodies. Residual viral proteins that remain within the cytoplasm of the host cell can be processed and presented at the cell surface on MHC class-I molecules, where they are recognised by T cells.
What happens after a viral genome is uncoated?
4. Replication: After the viral genome has been uncoated, transcription or translation of the viral genome is initiated.
Can viruses replicate without a host cell?
As viruses are obligate intracellular pathogens they cannot replicate without the machinery and metabolism of a host cell. Although the replicative life cycle of viruses differs greatly between species and category of virus, there are six basic stages that are essential for viral replication.