How do bacteriophages reproduce?
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By using some or all of the cellular machinery of the host cell.
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How do bacteriophages reproduce?
By using some or all of the cellular machinery of the host cell.
What are the main components of viruses?
Nucleic acids (DNA or RNA) and proteins.
Where are viral glycoproteins synthesized in the host cell?
In the rough endoplasmic reticulum (ER) and glycosylated by the Golgi apparatus.
What type of virus is the influenza virus?
An enveloped RNA virus.
What happens during the budding process?
The host cell membrane surrounds the nucleocapsid and pinches off to form the viral envelope.
What aids the new viruses in budding off from the host cell surface?
Neuraminidase.
How does antigenic shift differ from antigenic drift?
Antigenic shift involves major changes, while antigenic drift involves minor changes over time.
What is a key characteristic of retroviruses like HIV?
They reverse transcribe their RNA into DNA.
What are the two main glycoproteins found on the influenza viral envelope?
Haemagglutinin and neuraminidase.
What is the term used for the complex of RNA and proteins in the influenza virus?
Ribonucleoproteins.
What is formed when newly-synthesized capsomeres and accessory proteins assemble with viral RNA?
New nucleocapsids.
What other proteins and enzymes does the influenza viral genome code for?
RNA-dependent RNA polymerase, capsomeres, accessory proteins, etc.
How does neuraminidase facilitate the release of virions?
By cleaving the terminal sialic acid residues, thereby freeing the virions.
What is a virulent phage?
A phage that reproduces only via the lytic cycle.
What is antigenic shift?
A major change to the virus structure that creates new subtypes of influenza with new combinations of glycoproteins.
What is the primary function of T-helper cells in the immune system?
They are involved in the immune response and are targeted by HIV.
What serves as the viral genome?
The central core of nucleic acid.
What types of biomolecules are found in naked viruses?
Proteins and nucleic acids.
What are bacteriophages?
Viruses that infect bacteria.
Why is genetic reassortment undesirable?
It may produce new human influenza viruses with glycoproteins from avian or swine viruses, which the human immune system has not encountered.
What is a consequence of antigenic drift in influenza viruses?
Individuals can be infected by the same virus again.
What is the primary focus of the reproduction cycle of HIV?
The process by which HIV replicates within host cells.
What is the role of haemagglutinin in the influenza virus?
It mediates the attachment of the virus to the target cell and entry of the viral genome into the cell.
What happens after HIV attaches to the CD4 receptor?
The viral envelope fuses with the host cell membrane, releasing the nucleocapsid into the cytoplasm.
What is the role of reverse transcriptase in the HIV reproductive cycle?
It converts single-stranded RNA into double-stranded DNA.
What is a provirus in the context of HIV?
Integrated viral DNA that remains silent in the host DNA.
What triggers the transcription of the provirus in HIV-infected T-helper cells?
Activation of the host T-helper cell during an immune response.
What causes antigenic shift?
Genetic reassortment between different types of influenza viruses, often facilitated by species like pigs that can be infected by multiple types.
What happens during the replication phase of the T4 phage cycle?
The phage uses the host's DNA replication machinery to replicate its genome and synthesize viral proteins.
What type of parasites are viruses classified as?
Obligate intracellular parasites.
What are the structural components of viruses?
Including enveloped viruses and bacteriophages.
What is antigenic shift in the influenza virus?
A major change in the virus's surface proteins, leading to new strains.
How do viruses obtain their viral envelopes?
By budding from host cell membranes.
What glycoprotein on HIV binds to the CD4 receptor on host T-helper cells?
gp120.
What is the first step in the reproductive cycle of the T4 phage?
Attachment / Adsorption.
What are the three principles of the cell theory?
Are viruses considered living organisms?
No, viruses are not classified as living organisms.
What happens to the respiratory tract due to influenza infection?
Death of epithelial cells impairs functions like mucus clearance.
What types of nucleic acid can viruses have?
DNA or RNA.
What is the first step in the viral reproductive cycle?
Attachment/Adsorption, where the virus binds to specific receptors on the host cell.
What occurs after the phage DNA is replicated?
Phage proteins are produced and mature phages are assembled.
What type of phage is the lambda (λ) phage?
A temperate phage, as it reproduces via both lytic and lysogenic cycles.
What is a characteristic of the influenza virus?
It infects epithelial cells of the respiratory tract.
What materials does the host cell provide for viral replication?
Nucleotides, ribosomes, tRNAs, amino acids, ATP, and other raw materials.
What happens when T-helper cells are activated?
They release cytokines that stimulate the activity of macrophages, killer T cells, and B cells, which produce antibodies.
How do some viruses inject their nucleic acid into host cells?
By penetrating the cell membrane or injecting it into the cytoplasm.
What is the role of the capsid during phage infection?
It remains at the cell surface while viral DNA enters the host cell.
What is an example of an enveloped virus?
Influenza virus.
What type of virus is HIV?
A retrovirus.
What triggers the induction of the prophage?
Adverse external stimuli such as ionising radiation, UV radiation, toxic chemicals, or lack of nutrients.
What can antigenic shift result in?
The emergence of new influenza virus strains that can evade immunity.
What is the significance of the reproduction cycle in understanding HIV?
It helps in developing treatments and understanding the virus's behavior.
What do viruses lack that distinguishes them from cellular organisms?
Cytoplasm or organelles.
What forms a complex that is transported into the nucleus during influenza replication?
Accessory proteins and viral RNA.
What enzyme catalyzes the replication of single-stranded RNA in the nucleus?
RNA-dependent RNA polymerase.
How are enveloped viruses classified?
As viruses that have a lipid envelope.
What are naked viruses?
Viruses that do not have a lipid envelope.
What determines host specificity for the influenza virus?
The specificity between the viral glycoprotein (haemagglutinin) and the sialic acid receptor on epithelial cells.
What types of biomolecules are found in enveloped viruses?
Phospholipids, cholesterols, and viral glycoproteins.
Do viruses display characteristics of living organisms when outside a host cell?
No, they do not display many characteristics such as reproduction and metabolism.
What is a key difference in the entry step between influenza virus and HIV?
Influenza virus enters cells via endocytosis, while HIV fuses directly with the host cell membrane.
What is the final step for newly-formed nucleocapsids after assembly?
They leave the nucleus and are transported to the exit point at the cell surface membrane.
What role does lysozyme play in the exit/release phase of the T4 phage?
It hydrolyzes the peptidoglycan cell wall of the host bacterium, leading to cell lysis and release of new phages.
What happens during the activation of host cells infected by HIV?
Transcription of viral DNA into mRNA occurs, which is then translated into viral proteins.
How do T-helper cells become activated?
They recognize antigens presented by antigen presenting cells (APCs) on Class II MHC molecules with the help of CD4 receptors.
What role does HIV protease play in the viral life cycle?
It processes other HIV proteins into their functional forms.
What is the process called when the viral genome is released from the nucleocapsid?
Uncoating.
Which bacteriophage reproduces via both lytic and lysogenic cycles?
Lambda phage.
How many segments does the influenza viral genome consist of?
8 separate segments of single-stranded RNA.
What are viruses classified as?
The simplest biological systems.
What function does neuraminidase serve in the influenza virus life cycle?
It is involved in the release of newly formed influenza viruses from infected cells.
What is the size range of most viruses?
20-300 nm in diameter.
What are enveloped viruses?
Viruses that have an additional membrane outside the protein coat.
What begins the eclipse period in the T4 phage reproductive cycle?
The entry of viral DNA into the host bacterium.
What marks the beginning of the eclipse period in a lytic cycle?
The entry of viral DNA into the host cell.
What class of virus does HIV belong to?
Retrovirus.
What are T-helper cells?
A sub-group of lymphocytes involved in activating and directing other immune cells.
What happens to viruses when they infect a host cell?
They acquire the ability to display characteristics of living organisms by taking over the host's cellular machinery.
When does the eclipse period end?
When mature phages appear in the host cell.
How do viruses challenge the cell theory?
They challenge concepts of what is considered living.
How does the λ phage attach and enter the host bacterium?
The method of attachment and entry of the viral DNA is similar to the T4 phage.
What is the burst/rise period?
The time from the end of the latent period until all phages are released.
What happens during the assembly and maturation phase of viral reproduction?
Viral nucleic acid and proteins self-assemble into new nucleocapsids.
What is required for HIV to spread throughout the body?
The HIV reproductive cycle must not be interrupted by appropriate treatment.
What type of genetic material does the HIV genome consist of?
Two copies of linear, single-stranded RNA.
What is antigenic shift?
A significant change in viral antigens due to reassortment of genetic material.
What is a contractile sheath in complex phages like T4?
A structure that surrounds the tail and contracts during infection of the bacterium.
What type of virus is HIV?
A retrovirus.
What are the two alternative mechanisms by which phages reproduce?
Lytic cycle and lysogenic cycle.
What is the protein coat of a virus called?
Capsid.
What type of cells does the influenza virus target in mammals?
Epithelial cells of the respiratory tract.
How do viruses challenge the cell theory?
Viruses are non-cellular, smaller and more basic than cells, yet display some characteristics of life.
How is HIV transmitted?
Through the transfer of body fluids, such as blood or semen.
What is a key feature of a viral reproductive cycle?
It includes specific stages such as attachment, penetration, replication, assembly, and release.
Why does HIV have a high rate of mutation?
Because HIV reverse transcriptase is error-prone.
What happens when different types of influenza viruses infect the same pig host cell?
The progeny viruses may contain RNA segments from different virus types due to genetic reassortment.
What completes the maturation of new HIV viruses after their release?
HIV protease cuts viral polyproteins to form structural and enzymatic proteins.
What happens during the penetration/entry phase of viral reproduction?
The viral genome enters the host cell, with mechanisms varying by virus type and host cell.
What are viruses classified as?
Strict obligate intracellular parasites.
What is the risk associated with new types of human influenza viruses?
They may be able to transmit between humans, potentially leading to a global pandemic.
What is the latent period in a lytic cycle?
The time from the start of infection until mature phages are released.
What is the reproductive cycle of bacteriophages that reproduce via the lytic cycle?
An example is the T4 phage.
What is a lysogen?
An infected bacterium that harbors the prophage.
How do dormant viruses respond within a host cell?
They can respond to external signals to trigger reproduction.
What role do viral glycoproteins play in the budding process?
They are incorporated into the host cell membranes prior to budding.
What is the function of haemagglutinin in the release of new viruses?
It may attach to adjacent receptors containing sialic acid, preventing the release of new viruses.
How do viruses acquire their lipid envelope?
Through a process called budding when newly-formed viruses leave the host cell.
What are glycoprotein spikes?
Viral proteins incorporated into the lipid envelope that help attach the virus to specific host cell receptors.
What are the general features of viruses?
Viruses have unique structural components and reproductive cycles.
What characteristics define a living organism?
Order, homeostasis, response to stimuli, heredity, metabolism, reproduction, and evolution.
What is a similarity in the entry step between influenza virus and HIV?
Both viruses utilize specific receptors on host cells to facilitate entry.
How is the influenza virus primarily spread to host animals?
Through airborne transmission via aerosolized viral particles.
What are some symptoms caused by influenza infection?
Fever, sore throat, muscle pains, coughing, and in serious cases, pneumonia.
What is the latency period for HIV infection before symptoms typically appear?
8-10 years.
What is an antigen?
A substance that triggers an immune response, leading to the production of antibodies.
How does the influenza virus enter the host cell?
By endocytosis, forming an endocytic vesicle.
What is the role of T-helper cells in HIV infection?
HIV targets and destroys T-helper cells, compromising the immune system.
What was the death toll of the 1918 Spanish flu pandemic?
20 to 100 million.
What happens to the capsid coat during the entry of the influenza virus?
It is enzymatically removed, releasing viral RNA and proteins into the cytoplasm.
What symptoms of viral infections are caused by the body's immune response?
Symptoms such as fever and aches.
How does increased variation in viral genomes complicate eradication efforts?
It leads to the emergence of new viral strains that may evade immune responses and treatments.
What is a lipid envelope in viruses?
A lipid membrane composed of phospholipids and cholesterols, often derived from the host cell membrane.
What disease does the Human Immunodeficiency Virus (HIV) cause?
Acquired Immunodeficiency Syndrome (AIDS).
What is the central core of a virus composed of?
Nucleic acid surrounded by a protein capsid coat.
What are naked viruses?
Viruses that do not have a membrane.
Do new viruses grow from pre-existing viruses?
No, they do not undergo cell division and instead infect host cells to synthesize new viral components.
How are new HIV viruses released from the host cell?
By budding.
Which viral glycoproteins are affected by antigenic drift?
Haemagglutinin and neuraminidase.
What are the possible forms of nucleic acid in viruses?
Linear or circular, single- or double-stranded, and can exist as single or multiple molecules.
What role do T-helper cells play in the immune system?
They activate and direct other immune cells, making them crucial for immune response.
Why might antibodies from a previous influenza infection be ineffective against a new strain?
Due to mutations that alter the glycoproteins slightly.
What types of genomes do viruses have?
Viral genomes can be DNA/RNA, single/double-stranded, linear/circular, and may or may not have introns.
Do viruses carry out metabolism independently?
No, they cannot generate usable forms of energy like ATP on their own.
What enzyme does a retrovirus carry, and what is its function?
Reverse transcriptase; it catalyzes the synthesis of DNA from an RNA template.
How do naked and enveloped viruses exit the host cell?
Naked viruses usually exit via lysis of the host cell, while enveloped viruses exit through budding, often resulting in the death of the host cell.
What types of medications are currently used to contain HIV infection?
Inhibitors of reverse transcriptase and HIV protease.
What is the consequence of T-helper cell death due to HIV infection?
It impairs the immune system, leading to AIDS and inability to defend against opportunistic infections.
Do all phages have a base plate and tail fibres?
No, not all phages have these structures; others may use different structures on the capsid for binding.
What happens to the replicated complementary RNA strand in the nucleus?
It either stays to replicate more viral genome or is exported to the cytoplasm for protein translation.
How can the insertion of viral DNA into the host genome lead to cancer?
It can disrupt tumor suppressive genes or convert proto-oncogenes to oncogenes.
Why are pigs significant in the context of antigenic shift?
Pigs can be infected by avian, human, and swine influenza viruses, allowing for genetic reassortment.
What receptor does the influenza virus bind to on host cells?
Sialic acid on the surface of epithelial cells.
What happens to a person's immunity after recovering from an influenza virus infection?
They develop antibodies specific to the glycoproteins of that virus.
What does eradication of viral diseases refer to?
The permanent reduction to zero of the worldwide incidence of infection caused by a specific agent as a result of deliberate efforts.
What seasonal phenomenon is caused by antigenic drift?
Seasonal flu epidemics occurring every winter.
How are mature phages released from the host cell?
By cell lysis.
What is antigenic drift in influenza viruses?
It results in influenza viruses with slightly-modified glycoproteins.
What is the function of the endosome in the context of influenza virus entry?
It sorts substances taken in through endocytosis and has an acidic pH that aids in viral entry.
How does the T4 phage penetrate the bacterial cell wall?
By contracting the contractile sheath of the tail, driving the hollow tube into the host bacterium.
Where are viral glycoproteins synthesized?
In the rough endoplasmic reticulum (ER) and glycosylated by the Golgi apparatus.
What effect does a more active viral promoter have on proto-oncogenes?
It may cause over-expression, converting proto-oncogenes into oncogenes.
How do viruses reproduce?
By invading living host cells and hijacking their cellular machinery.
Where are viral glycoproteins inserted in the host cell?
Into the cell surface membrane at the exit point for viral release.
What is formed during the assembly and maturation phase of the T4 phage?
Mature phage particles are formed as protein components assemble around the viral genome.
How does variation in the viral genome arise?
It mostly arises due to mutations during the replication of the viral genome.
What triggers the entry of the influenza virus into the host cell?
A conformational change of the receptor after binding.
What is the approximate error rate of influenza RNA-dependent RNA polymerase?
1 per 10^3 - 10^5 nucleotides incorporated.
How do viral infections generally cause diseases?
By resulting in the death of host cells, leading to damage in host tissue and disruption of tissue functions.
What is the size range of most bacteriophages?
24-200 nm in length.
What role does haemagglutinin play in the entry of the influenza virus?
It facilitates the fusion of the viral envelope with the endosomal membrane.
How does variation in viral genomes arise?
Through processes like antigenic drift and antigenic shift.
What structure do viruses have that maintains their organized shape?
A capsid coat.
How does HIV target T-helper cells?
By binding glycoprotein gp120 to the specific CD4 receptor on T-helper cells.
What are the ultimate challenges in controlling the AIDS epidemic?
Developing medications to eradicate HIV and creating a vaccine to prevent new infections.
What causes the conformational change in haemagglutinin during viral entry?
The low pH within the endosome.
What components are found in the structure of HIV?
Proteins, enzymes like reverse transcriptase and integrase, a viral envelope, and glycoproteins.
What is antigenic drift?
A gradual process where mutations in viral RNA lead to changes in glycoproteins over time.
What happens during the eclipse period?
Infectious phages are not yet assembled inside the host cell.
What is the lytic cycle in bacteriophages?
A reproductive cycle where the virus replicates and causes the host cell to burst.
What is the significance of gp120 in HIV?
Different strains of HIV have slightly altered gp120, making antibodies against earlier strains ineffective.
What is the lysogenic cycle in bacteriophages?
A reproductive cycle where the viral DNA integrates into the host genome and replicates with it.
What are capsomeres?
Protein subunits that make up the capsid coat.
Who is at high risk for severe illness from influenza?
Children under age two, adults over age 65, and people with chronic lung diseases or weakened immune systems.
What is the error rate of HIV reverse transcriptase?
1 per 1700 nucleotides incorporated.
What happens to host cells during viral replication?
They are unable to synthesize essential proteins, leading to reduced cellular functions and cell death.
What is antigenic drift?
A gradual change in viral antigens due to mutations.
How do viral glycoproteins affect the immune response?
They may cause infected host cells to be recognized as foreign, leading to their destruction by immune cells.
What is integrated into the host DNA after reverse transcription?
The DNA produced by reverse transcription.
What is the function of tail fibres in bacteriophages?
They are involved in the attachment of the phage to specific receptors on the bacterial cell.
How do viruses like HIV and influenza cause diseases in humans?
By disrupting host tissue and functions.
What is the lysogenic cycle in relation to the lambda (λ) phage?
It involves the replication of only the phage genome without reproducing the entire phage particle or destroying the host bacterium.
Why might certain influenza subtypes have high lethality?
Due to massive immune responses triggered by high levels of viral reproduction.
What occurs during the replication phase of the viral reproductive cycle?
The virus uses host cell machinery to produce new viral components, including replication of the viral genome and expression of viral genes.
What is the function of the capsid coat?
To protect the nucleic acid, attach to host cell receptors, and enable penetration of the host cell membrane.
What role do host cells play in viral replication?
Viruses use the host cellular machinery for replication, inhibiting normal DNA, RNA, and protein synthesis.
What is formed when the capsid coat encloses the nucleic acid?
Nucleocapsid.
What is a prophage?
The integrated viral DNA within the host bacterium's chromosome.
Why are antibiotics sometimes prescribed for the common flu?
To prevent or treat secondary bacterial infections, even though the flu is caused by a virus.
What role does the tail of a bacteriophage play?
It contains a hollow tube through which viral DNA enters the host bacterium.
What role does the repressor protein play in the lysogenic cycle?
It prevents the transcription of most of the other prophage genes, keeping the phage genome mostly silent.
What are cytokines?
Small proteins that function as signaling molecules between cells of the immune system, triggering inflammation and regulating the immune response.
What causes variation in viral genomes?
Antigenic shift and antigenic drift.
What happens after the prophage exits the host bacterial chromosome?
The lytic cycle begins, resulting in the replication, assembly, and release of new λ phages, leading to the lysis and death of the host bacterium.
What occurs during the burst/rise period after the release of new phages?
A sharp rise in the number of infectious phage particles.
Why can't viruses reproduce on their own?
They lack the machinery to synthesize nucleic acids or proteins.
What challenges do antigenic drift and shift pose for influenza?
They result in different subtypes, making effective vaccination and antibody development difficult.
Why do viral enzymes have high error rates?
Due to the lack of proof-reading function.
What is a capsid head in bacteriophages?
A structure that contains the capsid coat made up of capsomeres and linear double-stranded DNA.
How do viruses reproduce within host cells?
By directing the host cell machinery to synthesize viral components.
What is antigenic shift in influenza viruses?
It results in influenza viruses with new combinations of glycoproteins.
What happens to the viral DNA within the host bacterium during the lysogenic cycle?
The linear viral DNA molecule circularises and integrates into a specific site on the host bacterial chromosome.
What is the approximate size of the T4 phage?
Approximately 200 nm long and 80-100 nm wide.
What is one consequence of the release of matured viruses from host cells?
It may result in cell death due to extensive loss of the cell surface membrane.
What allows viruses to undergo evolution?
They contain genes and can undergo spontaneous mutation.
How does the prophage replicate during bacterial division?
It replicates along with the host's DNA and is passed to daughter bacteria.
What triggers the formation of syncytia during HIV infection?
The insertion of newly-synthesized gp120 into the host cell surface membrane, leading to fusion with neighboring T-helper cells.
What additional components may be found in the viral genome?
Viral enzymes and proteins that stabilize the genome.
What happens to the RNA of HIV once it infects a cell?
It is used as a template to make double-stranded DNA.
What is syncytium in the context of HIV infection?
Giant multinucleated cells formed by the fusion of adjacent T-helper cells due to HIV infection.
What is the impact of impaired cellular functions on host tissues?
It results in disruption of host tissues and functions, leading to diseases.
