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Card 1
How did early scientists describe invisible infectious agents before the term 'virus' was widely adopted?
Prior to being able to see them, invisible infectious agents were described as 'contagium vivum fluidum,' meaning contagious living fluid. This term reflected the understanding that these agents were infectious and could spread disease, even though their nature was unknown.
Card 2
What significant technological advancement in the 1930s allowed scientists to directly observe viruses for the first time?
The advent of the electron microscope in the 1930s allowed scientists to directly observe viruses for the first time. This breakthrough enabled the study of their structure and replication, moving beyond the previous understanding of them as merely filterable agents.
Card 3
Define a 'virion' and explain its primary components.
A virion is a complete, fully developed, infectious viral particle that exists outside a host cell. It is composed of nucleic acid, which can be either DNA or RNA, and is surrounded by a protective protein coat called a capsid.
Card 4
How do viruses differ from bacteria in terms of their cellular machinery and energy generation?
Viruses are obligatory intracellular parasites, meaning they lack ribosomes and ATP-generating mechanisms, relying entirely on the host cell's machinery for multiplication. In contrast, bacteria are typically free-living organisms that possess their own ribosomes and ATP-generating systems.
Card 5
In what situation would the presence of spikes on a virus be particularly important for its infectivity?
Spikes are particularly important for viral infectivity during the attachment and entry phases into a host cell. For example, influenza viruses use hemagglutinin (H) spikes to attach to host cells and neuraminidase (N) spikes to detach from the cell surface during the release of new virions.
Card 6
How did Dmitri Ivanovsky's experiment with tobacco mosaic disease contribute to the understanding of viruses?
Dmitri Ivanovsky passed infected sap through a bacteria-proof filter and found that the filtrate still caused disease in healthy plants. This led him to conclude that the infectious agent was either a toxin or something smaller than bacteria, providing early evidence for the existence of filterable, non-bacterial pathogens.
Card 7
Distinguish between 'naked viruses' and 'enveloped viruses' based on their structural composition.
Naked viruses, also known as non-enveloped viruses, consist only of a nucleic acid genome surrounded by a protein capsid. Enveloped viruses, on the other hand, have their nucleic acid and capsid further surrounded by an outer lipid layer, which is a portion of the host cell's phospholipid membrane obtained during budding.
Card 8
Why are viruses considered 'obligatory intracellular parasites'?
Viruses are considered obligatory intracellular parasites because they absolutely require living host cells to multiply. They lack their own ribosomes and ATP-generating mechanisms, meaning they must utilize the host cell's synthesizing machinery to replicate their genetic material and produce new viral particles.
Card 9
What is the function of capsomeres in a virus?
Capsomeres are the individual protein subunits that make up the capsid, which is the protein coat surrounding the viral nucleic acid. These subunits assemble to form the protective structure that encloses the viral genome.
Card 10
How does the variety of viral nucleic acid differ from the nucleic acid found in cellular organisms?
Viral nucleic acid can be either DNA or RNA, but never both, and can be single-stranded or double-stranded, linear, circular, or segmented. In contrast, cellular organisms typically have double-stranded DNA as their genetic material, with RNA primarily serving as an intermediary.
Card 11
What role do the H and N spikes play in the identification of influenza viruses?
The H (hemagglutinin) and N (neuraminidase) spikes are specific protein structures on the surface of influenza viruses that allow them to attach to and detach from host cells. These spikes are crucial for viral infectivity and are often used as markers for identifying and classifying different strains of influenza viruses.
Card 12
Describe the general morphology of helical viruses, providing an example.
Helical viruses resemble long rods that can be either rigid or flexible, with their nucleic acid contained within a hollow, cylindrical capsid that has a helical structure. Examples of helical viruses include those that cause rabies and Ebola.
Card 13
Why was the term 'virus' (Latin for poison) adopted to describe these filterable agents by the 1930s?
The term 'virus,' meaning poison in Latin, was adopted to describe these filterable agents by the 1930s because scientists recognized their ability to cause disease and their infectious nature, even before their exact structure and biological mechanisms were fully understood. The term reflected their harmful effects on living organisms.
Card 14
What are the two main categories used to classify viruses based on their general composition?
Viruses are primarily classified into two categories based on their composition: naked viruses (or non-enveloped viruses), which consist only of nucleic acid and a capsid; and enveloped viruses, which have an additional outer lipid layer surrounding the capsid.
Card 15
How does the total amount of nucleic acid in a viral genome compare to that of a typical bacterial genome?
The total amount of nucleic acid in a viral genome is significantly smaller, varying from a few thousand nucleotides to as many as 250,000 nucleotides. This is much less than the millions of nucleotides found in a typical bacterial genome.
Card 16
What specific feature of some viruses allows them to detach from a host cell surface after replication?
Some viruses, like influenza, possess neuraminidase (N) spikes that allow them to detach from the host cell surface during the release of new virions. This enzyme helps in breaking down components of the host cell membrane, facilitating the exit of newly formed viral particles.
Card 17
Explain how the lipid layer of an enveloped virus is acquired.
The lipid layer of an enveloped virus, known as the viral envelope, is a small portion of the phospholipid membrane obtained from the host cell. This acquisition occurs as the virion buds from the host cell, essentially 'stealing' a piece of the host's membrane as it exits.
Card 18
What are the two primary components that make up a virion?
A virion is primarily composed of nucleic acid (either DNA or RNA) and a surrounding protein coat called a capsid. These two components form the complete, infectious viral particle.
Card 19
How does the structure of a helical virus accommodate its nucleic acid?
In a helical virus, the viral nucleic acid is found within a hollow, cylindrical capsid that has a helical structure. This arrangement allows the nucleic acid to be protected and contained along the length of the rod-shaped virus.
Card 20
What was Adolf Mayer's contribution to the early understanding of tobacco mosaic disease?
In 1886, Adolf Mayer investigated tobacco mosaic disease and found it to be infectious, but he was unable to identify the specific microbe causing it. His work established the infectious nature of the disease, setting the stage for further investigations into its causative agent.
Card 21
Why is the presence of a protein coat a distinctive feature of viruses?
The presence of a protein coat, or capsid, is a distinctive feature of viruses because it protects the viral nucleic acid genome and plays a crucial role in the attachment and entry of the virus into host cells. This coat is fundamental to the structure and function of all viruses.
Card 22
How do viruses multiply within a living host cell, given their lack of ribosomes and ATP-generating mechanisms?
Viruses multiply within living host cells by hijacking the host cell's synthesizing machinery. They use the host's ribosomes for protein synthesis and its ATP-generating mechanisms for energy, effectively reprogramming the cell to produce new viral components and assemble new virions.
Card 23
What is the significance of the fact that viral genomes can be single-stranded or double-stranded, and linear, circular, or segmented?
The diverse forms of viral genomes (single-stranded or double-stranded DNA or RNA, linear, circular, or segmented) highlight the remarkable adaptability and evolutionary strategies of viruses. This variety influences their replication mechanisms, host range, and overall pathogenicity.
Card 24
In what way do spikes on a virus contribute to its host specificity?
Spikes on a virus contribute to its host specificity by having structures at their tips that allow the virus to specifically attach to and enter certain types of cells. These structures act like keys, binding to specific receptors on the host cell surface, thus determining which cells the virus can infect.
Card 25
What is the primary method by which viruses are classified?
Viruses are primarily classified by their type of nucleic acid (DNA or RNA, single-stranded or double-stranded) and by differences in the structures of their protein coats, specifically the capsid morphology and the presence or absence of an envelope.
Card 26
Define 'enveloped viruses' and explain how they acquire their lipid layer.
Enveloped viruses are formed with a nucleic acid capsid surrounded by a lipid layer. This viral envelope is a small portion of the phospholipid membrane that the virion obtains as it buds from a host cell during its release.
Card 27
How do spikes on influenza viruses contribute to their infection cycle?
Influenza viruses use hemagglutinin (H) spikes to attach and enter a host cell. Neuraminidase (N) spikes, which are enzymes, allow the virus to detach from the cell surface during the release of new virions.
Card 28
Distinguish between mechanical and biological vectors in viral transmission.
Mechanical transmission occurs when an arthropod carries a viral pathogen on its body without being infected itself. Biological transmission, however, happens when the arthropod carries the viral pathogen inside its body, becoming infected and transmitting the virus to a new host.
Card 29
What is the primary characteristic of a polyhedral virus's capsid, and what is a common example?
The capsid of most polyhedral viruses is in the shape of an icosahedron, which is a regular polyhedron with 20 triangular faces and 12 corners. The capsomeres of each face form an equilateral triangle, and polio is an example of an icosahedral virus.
Card 30
In what situation would you classify a virus as 'complex'?
A virus is classified as 'complex' when it possesses complicated structures, particularly those seen in bacterial viruses like bacteriophages. These viruses often have capsids with additional attached structures such as tail sheaths, tail fibers, baseplates, and pins, which are not found in simpler helical or polyhedral forms.
Card 31
How is the host range of a virus determined?
The host range of a virus, which is the spectrum of host cells it can infect, is determined by specific host attachment sites and cellular factors. For bacteriophages, these receptor sites might be part of the bacterial cell wall, fimbriae, or flagella, while for animal viruses, they are typically on the plasma membrane.
Card 32
Why are influenza viruses often identified by their H and N spikes?
Influenza viruses are often identified by their H (hemagglutinin) and N (neuraminidase) spikes because these protein structures are crucial for the virus's ability to attach to host cells and then detach during the release of new virions. These spikes are key antigenic determinants that vary among different strains.
Card 33
How does the structure of a helical virus differ from that of a polyhedral virus?
Helical viruses resemble long rods with their nucleic acid found within a hollow, cylindrical capsid that has a helical structure. In contrast, polyhedral viruses, like icosahedrons, have a many-sided capsid with 20 triangular faces and 12 corners, giving them a more spherical appearance.
Card 34
What is the significance of the host cell's plasma membrane for animal viruses?
For animal viruses, the plasma membrane of the host cell is significant because it typically contains the receptor sites to which the virus attaches. This attachment is the crucial first step in the infection process, determining which specific cells or hosts the virus can infect.
Card 35
Explain how an enveloped helical virus, such as Marburgvirus, forms its structure.
An enveloped helical virus like Marburgvirus first forms its helical nucleocapsid, which is the nucleic acid enclosed within a helical capsid. This structure then becomes covered by an envelope, which is a lipid layer obtained from the host cell membrane as the virion buds, resulting in a roughly spherical shape.
Card 36
What role do fimbriae or flagella play in bacteriophage infection?
Fimbriae or flagella can serve as receptor sites for bacteriophages. These structures on the bacterial cell surface allow the bacteriophage to attach, which is the initial and critical step for the virus to infect the bacterium.
Card 37
How do protein structures called spikes facilitate viral entry into a cell?
Spikes, extending from the capsid on some naked and enveloped viruses, have structures at their tips that specifically allow the virus to attach to and enter a host cell. For example, influenza virus hemagglutinin spikes bind to host cell receptors, initiating the entry process.
Card 38
What does it mean for a virus to be transmitted through 'fomites'?
Transmission through fomites means that a virus is spread indirectly via inanimate objects that are contaminated with the pathogen. These objects, such as doorknobs or shared utensils, can harbor the virus and transfer it from an infected individual to a susceptible host.
Card 39
Describe the basic structure of a bacteriophage, a type of complex virus.
A bacteriophage is a complex virus characterized by a capsid, often referred to as a head, which contains the nucleic acid. Attached to this head are additional structures such as a tail sheath, tail fibers, a baseplate, and pins, which are involved in host cell attachment and nucleic acid injection.
Card 40
Why are viruses like rabies and Ebola classified as helical viruses?
Viruses like rabies and Ebola are classified as helical viruses because their viral nucleic acid is contained within a hollow, cylindrical capsid that has a helical structure. This gives them a characteristic long, rod-like appearance, which can be either rigid or flexible.
Card 41
How does the presence of an envelope affect the overall morphology of helical or polyhedral viruses?
When helical or polyhedral viruses are enclosed by an envelope, they are referred to as enveloped helical or enveloped polyhedral viruses. The presence of this lipid envelope typically makes the overall virion roughly spherical, regardless of the underlying capsid's shape.
Card 42
What is an icosahedron, and why is it relevant to virus morphology?
An icosahedron is a regular polyhedron with 20 triangular faces and 12 corners. It is relevant to virus morphology because the capsid of most polyhedral viruses, including many animal, plant, and bacterial viruses, is shaped like an icosahedron, with the capsomeres of each face forming an equilateral triangle.
Card 43
In what ways can viruses be transmitted from one host to another?
Viruses can be transmitted through direct contact, indirect contact with fomites (inanimate objects), or through a vector. Vectors are animals, such as arthropods like mosquitoes or ticks, that transmit a pathogen, either mechanically or biologically, from one host to another.
Card 44
What is the primary function of the structures at the tips of viral spikes?
The primary function of the structures at the tips of viral spikes is to allow the virus to attach to and enter a host cell. These structures facilitate the specific binding between the virus and host cell receptors, which is essential for initiating the infection process.
Card 45
Define 'host range' in the context of viral infection.
Host range refers to the specific spectrum of host cells that a virus is capable of infecting. Most viruses are highly selective, infecting only particular types of cells within a single host species, a specificity determined by attachment sites and cellular factors.
Card 46
Why is the phospholipid membrane obtained from a host cell important for enveloped viruses?
The phospholipid membrane obtained from a host cell forms the viral envelope, which surrounds the nucleocapsid of enveloped viruses. This envelope plays a crucial role in protecting the viral genome, facilitating entry into new host cells through membrane fusion, and often contains viral glycoproteins (spikes) for attachment.
Card 47
How do bacteriophages differ from animal viruses in terms of their receptor sites?
Bacteriophages typically use parts of the bacterial cell wall, fimbriae, or flagella as their receptor sites for attachment. In contrast, animal viruses usually utilize receptor sites found on the plasma membrane of their host cells.
Card 48
What does the term 'ds' indicate in the context of virus classification, and why is it important?
In virus classification, 'ds' indicates that the virus contains double-stranded nucleic acid. This is important because the type and strandedness (single or double) of the nucleic acid (DNA or RNA) are fundamental criteria for classifying viruses and influence their replication strategies.
Card 49
Give an example of a virus that exhibits an enveloped helical morphology.
Marburgvirus is an example of an enveloped helical virus. This means its genetic material is enclosed within a helical capsid, which is then surrounded by a lipid envelope derived from the host cell membrane.
Card 50
What is the role of 'seg' in the viral classification table?
In the viral classification table, 'seg' refers to segments of nucleic acid. This indicates that the virus's genome is not a single continuous molecule but is divided into multiple segments, which can affect its genetic variability and replication processes.
Card 51
How does antigenic drift allow viruses to evade the immune system?
Antigenic drift involves the accumulation of mutations in a virus over time, often due to the lack of proofreading mechanisms during replication. These genetic variations can lead to phenotypic changes in the virus, allowing it to alter its surface antigens and thus avoid detection and neutralization by the host's existing immune responses.
Card 52
Distinguish between mechanical and biological transmission of viruses by arthropods.
Mechanical transmission occurs when an arthropod carries a viral pathogen on the outside of its body and transmits it to a new host through physical contact. In contrast, biological transmission happens when the arthropod carries the viral pathogen inside its body and transmits it to the new host, typically through biting.
Card 53
What is the significance of understanding viral replication phases for drug development strategies?
Knowledge of viral replication phases is crucial for drug development because it allows researchers to identify specific steps in the viral life cycle that can be targeted by antiviral drugs. By disrupting processes like attachment, entry, biosynthesis, or release, drugs can inhibit viral multiplication and prevent disease progression.
Card 54
How does an animal virus typically enter a host cell?
Animal viruses typically enter host cells through receptor-mediated endocytosis or by fusion of the viral envelope with the host plasma membrane. These processes depend on specific receptor sites on the host cell's plasma membrane that the virus can bind to.
Card 55
What is a zoonosis, and provide an example.
A zoonosis is a disease that can be transmitted from an animal host to a human host. An example is the avian influenza virus, which originates in birds but has the potential to cause disease in humans.
Card 56
Explain the process of 'uncoating' in viral multiplication.
Uncoating is a crucial step in viral multiplication where the viral nucleic acid is released from its capsid. This process is facilitated by either viral enzymes or host enzymes, making the genetic material accessible for replication and protein synthesis.
Card 57
In what situation would a new virus subtype form due to antigenic shift?
A new virus subtype would form due to antigenic shift in RNA viruses that have segmented genomes, allowing them to exchange genetic material when different viruses infect the same host cell. This reassortment of RNA segments can lead to a completely novel virus with different antigenic properties, often with pandemic potential.
Card 58
What determines the specificity of a virus for its host cells?
The specificity of a virus for its host cells is determined by specific host attachment sites and cellular factors. Viruses can only infect cells that possess the appropriate receptor sites on their surface, which the viral proteins can bind to.
Card 59
Define 'reverse zoonosis' and provide an example.
Reverse zoonosis occurs when an animal is infected by a virus that originated in a human. The source notes do not provide a specific example for reverse zoonosis, but it generally describes the transmission of human pathogens to animals.
Card 60
How do enveloped viruses typically exit a host cell?
Enveloped viruses typically exit a host cell through a process called budding. During budding, the virus acquires its envelope from the host cell's membrane as it pinches off, allowing the virion to be released without immediately lysing the cell.
Card 61
What is the primary difference in genetic material for viruses classified as 'ds' versus 'ss'?
The primary difference is that 'ds' stands for double-stranded nucleic acid, meaning the virus carries its genetic information in two complementary strands. In contrast, 'ss' stands for single-stranded nucleic acid, indicating the virus's genetic material consists of only one strand.
Card 62
Why are arthropods considered typical vectors for viral diseases?
Arthropods such as mosquitoes, ticks, and flies are considered typical vectors for viral diseases because they can effectively transmit pathogens from one host to another. They can act as either mechanical vectors, carrying the virus externally, or biological vectors, carrying it internally and transmitting it through biting.
Card 63
How does the multiplication of animal viruses generally affect the host cell?
The multiplication of animal viruses generally causes significant changes to the host cell, often leading to its death. However, in some infections, cells can survive and continue to produce viruses indefinitely, establishing a persistent infection.
Card 64
What are 'fomites' and how do they relate to viral transmission?
Fomites are inanimate objects that can harbor and transmit infectious agents, including viruses. Viruses can be transmitted through indirect contact with fomites, meaning a person touches a contaminated object and then transfers the virus to themselves or another host.
Card 65
How does the entry mechanism of a pig retrovirus differ from that of a herpesvirus?
A pig retrovirus enters the host cell by receptor-mediated endocytosis, where the cell engulfs the virus in a vesicle. In contrast, a herpesvirus enters by fusion, where its viral envelope merges directly with the host cell's plasma membrane, releasing the capsid into the cytoplasm.
Card 66
What is the role of the host plasma membrane proteins in viral entry?
Host plasma membrane proteins serve as receptor sites for viruses, allowing them to attach to the cell. These proteins are crucial for initiating the entry process, whether through receptor-mediated endocytosis or fusion, by providing the specific binding sites that the virus recognizes.
Card 67
Why are some of the deadliest emerging pathogens in humans viruses?
Some of the deadliest emerging pathogens in humans are viruses because we currently have few effective treatments or drugs to deal with viral infections. This lack of therapeutic options makes them difficult to eradicate and control, contributing to their high mortality and morbidity rates.
Card 68
What is the final step in the multiplication cycle of animal viruses, and what happens during it?
The final step in the multiplication cycle of animal viruses is release. During this phase, newly formed virions exit the host cell, either by budding for enveloped viruses or by rupturing the cell for non-enveloped viruses, allowing them to infect new cells.
Card 69
How does the presence of 'seg' in virus classification indicate a characteristic of its nucleic acid?
The presence of 'seg' in virus classification indicates that the virus has segments of nucleic acid. This means its genetic material is not a single, continuous molecule but rather divided into multiple separate pieces, which is characteristic of some RNA viruses like influenza.
Card 70
What is a 'bacteriophage' and what are its typical receptor sites?
A bacteriophage is a type of virus that specifically infects bacteria. Its receptor sites, which determine where it attaches to the bacterial cell, may be part of the bacterial cell wall, or structures like fimbriae or flagella.
Card 71
Why is 'no proofreading' a key characteristic associated with antigenic drift?
No proofreading is a key characteristic associated with antigenic drift because it leads to a higher rate of mutations during viral replication. Without a mechanism to correct errors, genetic variations accumulate more rapidly, resulting in changes to viral antigens that help the virus evade the host immune system.
Card 72
What are the six general steps of viral replication in animals?
The six general steps of viral replication in animals are attachment, entry, uncoating, biosynthesis of nucleic acids and proteins, maturation, and release. These sequential steps describe the complete life cycle of a virus within a host cell.
Card 73
How does the assembly of nucleic acid and capsid proteins contribute to viral maturation?
During maturation, the assembly of nucleic acid and capsid proteins forms new, infectious virions. This process ensures that the viral genetic material is properly packaged within a protective protein shell, making the virus capable of surviving outside the host cell and infecting new ones.
Card 74
What is the primary outcome of antigenic shift concerning potential pandemics?
The primary outcome of antigenic shift is the formation of a new virus subtype, which carries a significant potential for causing pandemics. This is because the novel subtype often possesses antigens that are entirely unfamiliar to the human immune system, leading to widespread susceptibility and rapid global spread.
Card 75
Define the term 'transformation' in the context of oncogenic viruses.
Transformation refers to the process by which normal cells acquire distinct properties that lead to cancer. This occurs when oncogenic viruses integrate into the host cell's DNA, inducing tumors and altering cellular behavior.
Card 76
In what situation would understanding viral replication phases be particularly important for drug development?
Understanding viral replication phases is crucial for drug development when designing antiviral therapies. By targeting specific steps like attachment, entry, uncoating, biosynthesis, maturation, or release, drugs can effectively disrupt the viral life cycle and prevent infection or replication.
Card 77
Distinguish between a proto-oncogene and an oncogene.
Proto-oncogenes are normal genes that encode proteins involved in stimulating normal cell growth. When these proto-oncogenes undergo mutation, they become oncogenes, which then transform normal cells into cancerous cells by promoting uncontrolled growth.
Card 78
How does an enveloped virus typically achieve release from a host cell?
Enveloped viruses are typically released from a host cell through a process called budding. During budding, the viral capsid associates with the host cell's plasma membrane, acquiring a portion of the membrane to form its envelope as it exits the cell.
Card 79
Why are cancers caused by viruses generally not considered contagious?
Cancers caused by viruses are not considered contagious because the mechanism of cancer development involves the integration of viral DNA into the host cell's genome and subsequent cellular transformation, rather than direct transmission of cancerous cells themselves. The viral infection might be transmissible, but the cancer itself is not.
Card 80
What is the primary characteristic that defines a latent viral infection?
A latent viral infection is characterized by a virus remaining in equilibrium with the host without producing active disease for an extended period, often many years. The virus can persist within host cells, such as human herpes viruses, and may reactivate later under certain conditions like immunosuppression.
Card 81
How does the uncoating step contribute to viral replication?
Uncoating is a critical step in viral replication where viral or host enzymes remove the capsid, exposing the viral nucleic acid. This allows the viral genetic material to become accessible for the subsequent biosynthesis phase, where it can be replicated and transcribed.
Card 82
What is the significance of viral DNA being replicated and transcribed in the nucleus for a papovavirus?
For a papovavirus, the replication of viral DNA and transcription of mRNA in the nucleus are significant because it utilizes the host cell's nuclear machinery. This allows for the production of 'early' viral proteins necessary for further DNA replication and later, capsid proteins, all within the host's central genetic control center.
Card 83
In what way do oncogenic viruses induce tumors?
Oncogenic viruses induce tumors by becoming integrated into the host cell's DNA. This integration can disrupt normal cell growth regulation, often by affecting proto-oncogenes, leading to their transformation into oncogenes that promote uncontrolled cell proliferation and tumor formation.
Card 84
What are prions, and what is their infectious nature?
Prions are proteinaceous infectious particles, meaning they are infectious agents composed solely of protein. They are unique in that they are inherited and transmissible by ingestion, transplant, and surgical instruments, causing neurodegenerative diseases known as spongiform encephalopathies.
Card 85
How does a persistent viral infection differ from a latent viral infection?
A persistent viral infection occurs gradually over a long period, typically leading to fatal outcomes, where the virus is continuously present and often replicating. In contrast, a latent viral infection involves the virus remaining dormant for extended periods without causing active disease, though it can reactivate later.
Card 86
Why is the assembly of nucleic acid and capsid proteins crucial during the maturation phase of viral replication?
The assembly of nucleic acid and capsid proteins during the maturation phase is crucial because it forms new, infectious virions. Without this precise assembly, the viral genetic material would not be properly packaged and protected, preventing the virus from successfully infecting new host cells.
Card 87
What is the role of 'early' viral proteins in the replication cycle of a DNA-containing virus like papovavirus?
In the replication cycle of a DNA-containing virus like papovavirus, 'early' viral proteins are synthesized from mRNA transcribed from a portion of the viral DNA. These proteins are typically involved in facilitating viral DNA replication and regulating host cell functions to favor viral production.
Card 88
Describe the process of biosynthesis in viral replication.
Biosynthesis in viral replication is the phase where the virus produces its nucleic acid and proteins. This involves the replication of the viral genome and the transcription and translation of viral genes to synthesize all the components needed for new virions, often utilizing the host cell's machinery.
Card 89
What are spongiform encephalopathies, and what causes them?
Spongiform encephalopathies are a group of neurodegenerative diseases characterized by sponge-like holes in the brain tissue. They are caused by prions, which are misfolded proteins that can induce normal proteins to misfold, leading to progressive brain damage.
Card 90
How can immunosuppression lead to a fatal outcome in individuals with latent herpes virus infections?
Immunosuppression, such as in AIDS patients, can lead to the reactivation of latent herpes viruses. When the immune system is compromised, it can no longer keep the virus in check, allowing it to replicate actively and cause severe, potentially fatal, infections.
Card 91
Why is the attachment phase essential for viral replication?
The attachment phase is essential for viral replication because it is the initial step where the virion specifically binds to receptors on the host cell surface. This specificity ensures that the virus infects the correct host cells and is a prerequisite for subsequent entry into the cell.
Card 92
What is the primary difference in how enveloped and non-enveloped viruses are released from a host cell?
Enveloped viruses are typically released by budding, where they acquire a portion of the host cell membrane as their envelope during exit. Non-enveloped viruses, lacking an envelope, are generally released by rupture of the host cell, leading to cell lysis.
Card 93
How does the concept of 'viral protein' relate to the budding process of an enveloped virus?
During the budding process of an enveloped virus, viral proteins are often inserted into the host cell's plasma membrane. These viral proteins play a crucial role in directing the viral capsid to the membrane and facilitating the formation of the bud, which eventually pinches off to release the new enveloped virion.
Card 94
What cultural practice was historically associated with the transmission of Kuru?
Kuru was historically associated with certain cultural practices of cannibalism. Specifically, it was transmitted through the consumption of infected brain tissue during funerary rituals among the Fore people of Papua New Guinea.
Card 95
Why are some viral infections referred to as 'chronic' viral infections?
Some viral infections are referred to as 'chronic' viral infections because they persist gradually over a long period, often for the lifetime of the host. These are also known as persistent viral infections and typically lead to severe, often fatal, outcomes due to ongoing viral activity.
Card 96
How does the integration of oncogenic viruses into host DNA contribute to cancer development?
The integration of oncogenic viruses into host DNA can lead to cancer development by altering the expression of host genes, particularly proto-oncogenes. This can result in uncontrolled cell proliferation and the acquisition of cancerous properties, transforming normal cells into malignant ones.
Card 97
What is the role of the host cell plasma membrane in the entry of herpesvirus?
In the entry of herpesvirus, the host cell plasma membrane plays a direct role through fusion. The viral envelope fuses with the host plasma membrane, allowing the viral capsid and its contents to be released directly into the host cell's cytoplasm.
Card 98
Why might a virus remain in equilibrium with a host for many years without causing disease?
A virus might remain in equilibrium with a host for many years without causing disease because it enters a latent state. In this state, the viral genome is present but not actively replicating or producing virions, often kept in check by the host's immune system, only to reactivate under specific conditions like immunosuppression.
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