6.2 The Viral Life Cycle
4 min read•june 18, 2024
Viruses are fascinating microorganisms that hijack host cells to replicate. They employ various life cycles, from lytic to lysogenic, and use clever strategies to evade immune responses. Understanding viral is crucial for developing treatments and vaccines.
Viral infections can have profound impacts on host organisms. From causing direct cell damage to triggering autoimmune responses, viruses shape the health of individuals and populations. They even play a role in bacterial evolution through , highlighting their ecological importance.
Viral Life Cycles and Replication
Lytic vs lysogenic cycles
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- involves virus entering host cell, replicating, and lysing the cell to new virions occurs in () and most animal viruses (influenza)
- Steps include , , replication, , and release
- involves integrating into host cell's genome as a host cell replicates normally, passing the to daughter cells
- Prophage can be induced to enter the under certain conditions (UV light, chemicals)
- Occurs in () and some animal viruses ()
Key steps in virus replication
- Attachment: virus binds to specific receptors on the host cell surface (influenza binds to sialic acid receptors)
- : virus enters the cell via or ( uses )
- : viral genome is released into the cytoplasm or nucleus ( uncoats in the nucleus)
- Replication: viral genome is replicated using host cell machinery
- DNA viruses typically replicate in the nucleus ()
- RNA viruses typically replicate in the cytoplasm ()
- Assembly: new viral components are synthesized and assembled into virions ( assembles in the cytoplasm)
- Release: new virions are released from the host cell via or budding (influenza buds from the cell membrane)
- occurs during this stage, allowing for transmission to new hosts
Viral Structure and Host Interactions
- : lipid bilayer surrounding some viruses, derived from host cell membranes ()
- : protein shell that encases the viral genome, providing protection and facilitating entry into host cells (adenovirus)
- Viral genome: genetic material of the virus, can be DNA or RNA (viral genome of hepatitis B virus is partially double-stranded DNA)
- : specific molecule on the cell surface that viruses bind to for entry (host cell receptor ACE2 for SARS-CoV-2)
- : the ability of a virus to infect specific cell types or tissues, determined by the presence of appropriate receptors and cellular factors
Retroviruses vs latent viruses
- are RNA viruses that use to convert their RNA genome into DNA viral DNA integrates into the host cell's genome as a
- is transcribed and translated to produce new virions (HIV)
- have a viral genome that remains dormant within the host cell without causing apparent symptoms
- Can reactivate and enter the lytic cycle under certain conditions like stress or immunosuppression ( causing )
- : the ability of some viruses to remain in the host for extended periods, either through latency or chronic active infection (hepatitis B virus)
Human virus-host cell interactions
- Viruses exploit host cell receptors for attachment and entry (HIV uses CD4 and / receptors)
- Viruses hijack host cell machinery for replication and protein synthesis (influenza uses host cell ribosomes)
- Some viruses inhibit host cell protein synthesis to prioritize viral protein production ()
- Viruses can evade or suppress the host immune response through various mechanisms
- and shift (influenza)
- Inhibition of interferon production or signaling ()
- Downregulation of MHC class I molecules ()
Transduction in gene transfer
- Transduction transfers genetic material from one bacterium to another via a virus ()
- Types of transduction
- : any bacterial DNA can be packaged into the phage capsid and transferred ()
- : specific bacterial genes adjacent to the prophage are transferred (lambda phage)
- Contributes to the spread of antibiotic resistance (beta-lactamase genes) and virulence factors (toxin genes) among bacterial populations
Plant virus replication cycle
- Attachment: often enter through wounds or insect vectors (aphids, whiteflies)
- Penetration: viruses move from cell to cell through ()
- Replication occurs in the cytoplasm
- Most plant viruses are RNA viruses and replicate in the cytoplasm ()
- Some DNA plant viruses replicate in the nucleus ()
- Assembly: new virions are assembled in the cytoplasm ()
- Release: virions are released by cell lysis or through plasmodesmata to neighboring cells ()
- Plant viruses do not typically undergo latent or lysogenic cycles
Host-Virus Interactions and Consequences
Human virus-host cell interactions
- Viruses can cause direct cytopathic effects, leading to cell damage or death
- Cell lysis (adenovirus)
- formation (measles virus)
- Inclusion bodies (rabies virus)
- Viruses can induce (programmed cell death) or (premature cell death) in host cells
- Persistent infections can lead to chronic inflammation and tissue damage ()
- Viral infections can trigger autoimmune responses ( and multiple sclerosis)
- Some viruses are oncogenic and can cause cellular transformation and cancer
- (cervical cancer)
- Hepatitis B and C viruses (liver cancer)
- (, nasopharyngeal carcinoma)
Transduction in gene transfer
- Transduction facilitates the evolution and adaptation of bacterial populations
- Acquisition of new metabolic capabilities (lactose fermentation genes)
- Development of antibiotic resistance (methicillin resistance in Staphylococcus aureus)
- Enhanced virulence or survival mechanisms (Shiga toxin genes in E. coli)
- Transduction contributes to the genetic diversity and ecological success of bacteria
Key Terms to Review (110)
+ssRNA: +ssRNA, or positive-sense single-stranded RNA, is a type of viral genetic material that can act directly as mRNA in host cells. This allows for immediate translation by the host's ribosomes during infection.
Adenovirus: Adenoviruses are a group of non-enveloped, double-stranded DNA viruses that can infect a variety of host cells, including those in the human gastrointestinal tract. These viruses are known for their ability to cause a range of illnesses, from common colds to more severe respiratory and gastrointestinal diseases.
Antigenic Drift: Antigenic drift is a gradual, continuous process of genetic changes that occur in the surface proteins of viruses, particularly influenza viruses, leading to the emergence of new viral strains. This evolutionary mechanism allows the virus to evade the host's immune system and cause recurring infections.
Antigenic Shift: Antigenic shift is a major, abrupt, and unexpected change in the surface antigens of a virus, particularly in influenza viruses. This phenomenon results in the emergence of a new viral strain that is significantly different from previous strains, often leading to the potential for widespread outbreaks and pandemics.
Apoptosis: Apoptosis is a highly regulated form of programmed cell death that occurs in multicellular organisms. It is a crucial process involved in various aspects of the immune system, viral life cycles, and cellular defenses against disease.
Assembly: Assembly is the process by which a viral particle is constructed from its individual components, including the viral genome, structural proteins, and other necessary elements. This crucial step in the viral life cycle is responsible for the formation of complete, infectious viral particles that can then be released from the host cell to infect new cells.
Attachment: Attachment is the process by which a virus binds to specific receptor molecules on the surface of a host cell. This interaction is critical for viral entry and subsequent infection.
Bacteriophage: A bacteriophage, or phage, is a virus that infects and replicates within bacteria. Phages are the most abundant biological entities on Earth and play a crucial role in the ecology and evolution of bacterial communities, as well as in the discovery of the secrets of life through microbiology.
Biosynthesis: Biosynthesis is the process by which living organisms produce complex molecules from simpler ones. It involves various enzymatic reactions to build cellular components.
Brome mosaic virus: Brome mosaic virus (BMV) is a positive-sense, single-stranded RNA virus that infects various plant species, particularly grasses and cereal crops. It is a member of the Bromoviridae family and is known for its ability to replicate and spread efficiently within its host plants.
Burkitt's Lymphoma: Burkitt's lymphoma is an aggressive type of non-Hodgkin's lymphoma, a cancer of the lymphatic system. It is characterized by the rapid growth of malignant B cells and is often associated with Epstein-Barr virus (EBV) infection. Burkitt's lymphoma is particularly relevant in the context of the viral life cycle, as the Epstein-Barr virus plays a crucial role in its development and progression.
Burst: Burst refers to the release of new viral particles from a host cell after replication. This process often results in the lysis or death of the host cell.
Burst size: Burst size is the number of viral particles released when a host cell bursts at the end of the lytic cycle. It represents the productivity of viral replication within a single infected cell.
Capsid: The capsid is the protein shell that encloses the genetic material of a virus. It is a crucial structural component that protects the viral genome and facilitates the virus's ability to infect host cells during the viral life cycle.
Cauliflower mosaic virus: Cauliflower mosaic virus (CaMV) is a plant virus that infects members of the Brassicaceae family, including cauliflower, broccoli, and Brussels sprouts. It is a double-stranded DNA virus that replicates in the nucleus of infected plant cells and can cause mosaic-like patterns and stunted growth in its host plants.
CCR5: CCR5 is a chemokine receptor that serves as a co-receptor for the entry of HIV-1 into host cells, playing a crucial role in the viral life cycle. It is expressed on the surface of various immune cells, including T cells, macrophages, and dendritic cells, and its interaction with the HIV-1 envelope protein is a critical step in the virus's ability to infect and replicate within these cells.
Chickenpox: Chickenpox is a highly contagious viral infection caused by the varicella-zoster virus, characterized by an itchy rash and red spots or blisters. It primarily affects children but can occur in individuals of any age.
Chronic infection: A chronic infection is a persistent infection caused by pathogens that can evade the host's immune system, leading to prolonged disease. Such infections often result in continuous or recurrent symptoms over an extended period.
Citrus tristeza virus: Citrus tristeza virus (CTV) is a plant pathogenic virus that affects citrus trees, causing severe economic losses. It belongs to the Closteroviridae family and is transmitted by aphids.
Cucumber mosaic virus: Cucumber mosaic virus (CMV) is a plant pathogenic virus belonging to the genus Cucumovirus. It infects a wide range of host plants, leading to significant agricultural losses.
Cucumber mosaic virus: Cucumber mosaic virus (CMV) is a plant virus that infects a wide range of herbaceous plants, including cucumbers, melons, tomatoes, and many other vegetables and ornamental plants. It is one of the most economically important plant viruses, causing significant crop losses worldwide.
CXCR4: CXCR4 is a chemokine receptor that plays a crucial role in the viral life cycle. It is a G-protein coupled receptor that serves as a co-receptor for the entry of HIV-1 into host cells, facilitating the virus's ability to infect and replicate within the body.
Cytomegalovirus: Cytomegalovirus (CMV) is a type of herpes virus that can infect and remain dormant within the human body. It is a significant concern for individuals with weakened immune systems, as it can cause severe and potentially life-threatening infections.
DsDNA: Double-stranded DNA (dsDNA) consists of two complementary strands that form the double helix structure of DNA. It is the genetic material for many organisms, including some viruses.
DsRNA: dsRNA stands for double-stranded RNA, a molecule consisting of two complementary strands of RNA. It is often involved in the replication and lifecycle of certain viruses.
Ebola epidemics: Ebola epidemics are outbreaks of Ebola virus disease (EVD), a severe and often fatal illness caused by the Ebola virus. These epidemics typically occur in sporadic outbreaks primarily in sub-Saharan Africa.
Ebola Virus: The Ebola virus is a highly contagious and often fatal viral infection that primarily affects humans and other primates. It is a member of the Filoviridae family, known for its unique filamentous shape and ability to cause severe hemorrhagic fever. The Ebola virus is a significant public health concern due to its high mortality rate and the potential for rapid spread in the absence of effective treatment or vaccine.
Eclipse phase: The eclipse phase is a period during the viral life cycle when the virus has entered a host cell but new virions have not yet been formed. During this phase, viral components are being synthesized and assembled.
Endocytosis: Endocytosis is a cellular process in which substances are brought into the cell by engulfing them in a vesicle. This process allows cells to take in large molecules, particles, or even other cells.
Endocytosis: Endocytosis is the process by which cells bring materials into their interior by engulfing them with their cell membrane. It is a crucial mechanism for the uptake of nutrients, signaling molecules, and even pathogens, and is a key step in the viral life cycle.
Epstein-Barr virus: Epstein-Barr virus (EBV) is a herpesvirus that primarily infects B cells and epithelial cells, causing mononucleosis. It is associated with several cancers, including Burkitt's lymphoma and nasopharyngeal carcinoma.
Epstein-Barr Virus: Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that primarily infects and establishes lifelong latent infection in B lymphocytes. It is associated with various clinical manifestations, including infectious mononucleosis, autoimmune disorders, and immunodeficiency.
Generalized transduction: Generalized transduction is a process by which bacteriophages transfer bacterial DNA from one bacterium to another during infection. This mechanism can result in genetic recombination in the recipient bacteria.
Generalized Transduction: Generalized transduction is a process in which any bacterial DNA can be packaged into a bacteriophage (viral) particle and transferred to another bacterial cell, allowing for the exchange of genetic material between unrelated bacteria. This mechanism contributes to the genetic diversity of asexual prokaryotes.
Hemagglutinin: Hemagglutinin is a glycoprotein found on the surface of certain viruses, such as influenza viruses, that allows the virus to bind to and agglutinate (clump together) red blood cells. This crucial step in the viral life cycle facilitates the virus's ability to infect host cells and spread throughout the body.
Hepatitis B Virus: The hepatitis B virus (HBV) is a highly contagious DNA virus that primarily infects the liver, causing inflammation and potential long-term liver damage. It is a significant global health concern, as chronic HBV infection can lead to cirrhosis and liver cancer if left untreated.
Hepatitis C virus: Hepatitis C virus (HCV) is a bloodborne virus that primarily infects the liver, causing both acute and chronic hepatitis. It is an RNA virus classified within the Flaviviridae family.
Herpes simplex virus: Herpes simplex virus (HSV) is a double-stranded DNA virus that causes infections in humans, characterized by latent and recurrent infections. There are two main types: HSV-1 primarily causes oral herpes, while HSV-2 mainly causes genital herpes.
Herpes Simplex Virus: Herpes simplex virus (HSV) is a highly contagious virus that can cause a variety of infections, primarily affecting the skin, mucous membranes, and nervous system. It is a member of the Herpesviridae family and is a common cause of viral infections in humans, with two main types: HSV-1 and HSV-2.
HIV: HIV (Human Immunodeficiency Virus) is a virus that targets the immune system, specifically CD4 cells (T cells), leading to a progressive failure of the immune system. If left untreated, HIV can lead to AIDS (Acquired Immunodeficiency Syndrome).
Host Cell Receptor: A host cell receptor is a protein molecule located on the surface of a host cell that can bind to specific molecules or ligands, including those from pathogens like viruses. These receptors act as docking sites, allowing the pathogen to attach to and enter the host cell, initiating the viral life cycle.
Human Papillomavirus: Human papillomavirus (HPV) is a group of viruses that can infect the skin and mucous membranes, leading to a variety of diseases, including warts, precancerous lesions, and certain types of cancer. HPV is a significant topic in the context of viruses, the viral life cycle, the anatomy and microbiota of the urogenital tract, and viral infections of the reproductive system.
Induction: Induction is the process by which a dormant virus in a lysogenic cycle becomes active and enters the lytic cycle. This shift leads to the production of new viral particles and often results in the destruction of the host cell.
Influenza virus: Influenza virus is an RNA virus that causes the contagious respiratory illness known as the flu. It primarily infects the nose, throat, and occasionally the lungs, leading to symptoms like fever, cough, and body aches.
Influenza Virus: The influenza virus is a type of RNA virus that causes the contagious respiratory illness known as the flu. It is a member of the Orthomyxoviridae family and is a significant public health concern due to its ability to cause seasonal epidemics and occasional global pandemics.
Lambda Phage: Lambda phage is a type of bacteriophage, a virus that infects and replicates within bacterial cells. It is a well-studied model organism that has provided important insights into viral life cycles, genetic engineering, and the interactions between viruses and their bacterial hosts.
Latent infection: A latent infection is a type of viral infection where the virus remains in the host's body in an inactive state and does not produce symptoms. The virus can reactivate later, causing disease.
Latent virus: A latent virus is a virus that enters a state of dormancy within the host cell and does not replicate immediately after infection. It can reactivate later to produce new viral particles.
Latent Viruses: Latent viruses are a type of persistent viral infection where the virus remains dormant or inactive within the host's cells, often without causing any immediate symptoms. These viruses can reactivate under certain conditions, leading to the production of new viral particles and potential disease recurrence.
Lysis: Lysis is the process by which a cell breaks down and releases its contents, often due to viral infection. It typically results in the destruction of the host cell's membrane.
Lysogen: A lysogen is a bacterial cell that harbors a prophage, which is a viral genome integrated into the host DNA. The prophage can remain dormant until it is induced to enter the lytic cycle.
Lysogenic conversion: Lysogenic conversion is a process where a bacterium acquires new genetic traits from a temperate phage during lysogeny. These new traits can sometimes enhance bacterial virulence or other characteristics.
Lysogenic cycle: The lysogenic cycle is a viral reproductive cycle in which the viral DNA is incorporated into the host cell's genome, where it can remain dormant for an extended period. It does not immediately destroy the host cell.
Lysogenic Cycle: The lysogenic cycle is a mode of viral reproduction in which the viral genome becomes incorporated into the host cell's DNA, allowing the virus to replicate along with the host cell's genetic material without immediately causing the host cell to lyse or burst open. This cycle is one of the two main viral life cycles, the other being the lytic cycle.
Lysogeny: Lysogeny is a viral reproductive cycle in which the virus's genome is integrated into the host's genome, where it can remain dormant. This phase can eventually lead to the lytic cycle under certain conditions.
Lytic animal viruses: Lytic animal viruses are viruses that infect animal cells and cause the lysis (destruction) of the host cell during their replication cycle. This results in the release of new viral particles.
Lytic cycle: The lytic cycle is a viral replication process that results in the destruction of the host cell and the release of new virus particles. This cycle consists of five main stages: attachment, penetration, biosynthesis, maturation, and lysis.
Lytic Cycle: The lytic cycle is a mode of viral replication in which the virus infects a host cell, hijacks its cellular machinery to produce more viral particles, and then lyses or bursts the host cell to release the newly formed virions. This cycle is in contrast to the lysogenic cycle, where the viral genome is integrated into the host's DNA and remains dormant until induced to enter the lytic phase.
Maturation: Maturation is the process by which viral particles undergo structural changes to become fully infectious. This step often involves proteolytic cleavage and assembly of viral components.
Membrane fusion: Membrane fusion is the process by which two lipid bilayers merge to form a single continuous membrane. This is crucial for viral entry into host cells, allowing the viral genome to access the cellular machinery.
Membrane Fusion: Membrane fusion is a fundamental biological process in which two lipid bilayer membranes merge to form a single continuous membrane. This process is critical for various cellular events, including viral entry, neurotransmitter release, and vesicle trafficking.
Necrosis: Necrosis is the death of cells or tissues in a living organism, often caused by injury, disease, or lack of blood supply. It is a key feature of many viral infections and plays a crucial role in the viral life cycle.
Negative (−) single-strand RNA (−ssRNA): Negative single-strand RNA (−ssRNA) is a type of viral RNA that requires conversion to positive-sense RNA before it can be translated by host ribosomes. This conversion is carried out by an RNA-dependent RNA polymerase.
One-step multiplication curve for bacteriophage: A one-step multiplication curve for bacteriophage is a graphical representation that illustrates the replication cycle of a bacteriophage within a host cell. It typically includes phases such as adsorption, eclipse, and burst.
P1 Phage: P1 phage is a temperate bacteriophage, a virus that infects and replicates within bacterial cells. It is commonly used as a model system to study the viral life cycle and as a tool in genetic engineering for its ability to transduce genetic material between bacterial hosts.
Penetration: Penetration is the process by which a virus enters a host cell after attachment. This step is crucial for the viral life cycle as it allows the viral genome to access the host's cellular machinery.
Penetration: Penetration, in the context of the viral life cycle, refers to the process by which a virus gains entry into a host cell. This crucial step allows the viral genetic material to be delivered into the cell, enabling the virus to hijack the host's cellular machinery and replicate itself.
Persistent infection: A persistent infection is a type of viral infection where the virus remains in the host body for an extended period, often for the lifetime of the host. This can occur with or without symptoms and can involve continuous or intermittent viral shedding.
Phage conversion: Phage conversion is a process where a bacterium acquires new traits due to the integration of prophage DNA into its genome. This can result in changes such as increased virulence or antibiotic resistance.
Plant viruses: Plant viruses are microscopic infectious agents that infect plants, causing various diseases and economic losses in agriculture. They consist of genetic material (DNA or RNA) surrounded by a protein coat and rely on host machinery for replication.
Plasmodesmata: Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, allowing for the intercellular transport of materials and the communication between adjacent cells. These structures are essential for the coordination and integration of cellular activities within the plant organism.
The term 'plasmodesmata' is particularly relevant in the context of the viral life cycle, as these channels can serve as pathways for the movement and spread of plant viruses between cells.
Poliovirus: Poliovirus is a highly infectious virus that primarily targets the human nervous system, causing poliomyelitis. It is an RNA virus belonging to the enterovirus genus of the Picornaviridae family.
Poliovirus: Poliovirus is a highly contagious virus that primarily infects the gastrointestinal tract and can lead to the debilitating disease polio. It is a member of the Picornaviridae family and is the causative agent of the viral infection known as poliomyelitis.
Positive (+) single-strand (+ssRNA): Positive single-strand RNA (+ssRNA) viruses have genomes that can directly serve as mRNA for protein synthesis. They are immediately infectious upon entering a host cell.
Potato Virus Y: Potato Virus Y (PVY) is a plant virus that primarily infects potato crops, causing significant economic losses for farmers. It is a member of the Potyvirus genus and is one of the most economically important viral pathogens affecting potato production worldwide.
Progeny virus: A progeny virus is a new virus particle that has been produced by the replication cycle of an existing virus within a host cell. These particles are capable of infecting new cells and propagating the viral infection.
Prophage: A prophage is a bacteriophage genome integrated into the DNA of a bacterial host. It remains dormant until triggered to enter the lytic cycle.
Prophage: A prophage is a bacteriophage (virus that infects bacteria) genome that has been integrated into the DNA of a host bacterial cell. It exists in a dormant state, replicating along with the host's chromosome, until conditions trigger its activation and entry into the lytic cycle.
Provirus: A provirus is a viral genome that integrates into the DNA of a host cell. It can remain latent for extended periods before becoming active and producing new virus particles.
Provirus: A provirus is the integrated form of a virus's genetic material within the genome of a host cell. It represents the dormant or latent stage of a viral life cycle, where the viral DNA becomes incorporated into the host's DNA, allowing the virus to persist and potentially reactivate at a later time.
Release: Release refers to the final stage of the viral life cycle where newly assembled viral particles are expelled from the host cell, allowing them to infect new host cells and propagate the viral infection.
Replication: Replication is the process by which a cell or virus makes an identical copy of its genetic material, ensuring the faithful transmission of genetic information to its offspring. This fundamental biological process is essential for the propagation and evolution of all living organisms.
Retrovirus: A retrovirus is an RNA virus that inserts a copy of its genome into the DNA of a host cell, thereby changing the cell's genetic makeup. This process is facilitated by the enzyme reverse transcriptase.
Retroviruses: Retroviruses are a unique class of viruses that use RNA as their genetic material and employ a reverse transcriptase enzyme to convert their RNA into DNA, which is then integrated into the host cell's genome. This distinctive life cycle and genetic structure allows retroviruses to persistently infect their hosts and utilize the cellular machinery for their own replication.
Reverse transcriptase: Reverse transcriptase is an enzyme that synthesizes complementary DNA (cDNA) from an RNA template. It is essential for the replication of retroviruses, including HIV.
Reverse Transcriptase: Reverse transcriptase is an enzyme found in retroviruses, such as HIV, that is responsible for converting the viral RNA genome into DNA. This process is a crucial step in the viral life cycle, allowing the viral genetic material to be integrated into the host cell's genome.
RNA-dependent RNA polymerase (RdRP): RNA-dependent RNA polymerase (RdRP) is an enzyme that catalyzes the replication of RNA from an RNA template. It is essential for the life cycle of RNA viruses.
Shingles: Shingles, also known as herpes zoster, is a viral infection caused by the reactivation of the varicella-zoster virus (VZV), which also causes chickenpox. It is characterized by a painful rash that typically appears on one side of the body or face.
Specialized transduction: Specialized transduction is a process where a bacteriophage transfers specific portions of the bacterial genome to another bacterium. This occurs during the lysogenic cycle when prophage excision includes adjacent bacterial genes.
Specialized Transduction: Specialized transduction is a type of genetic recombination in bacteria where a bacteriophage (virus that infects bacteria) incorporates a small segment of the host's DNA into its own genome and then transfers that genetic material to a new bacterial host during the viral infection process. This allows for the exchange of genetic information between bacteria and can contribute to the acquisition of new traits, such as antibiotic resistance or virulence factors.
SsDNA: ssDNA stands for single-stranded DNA, which is a DNA molecule consisting of only one strand as opposed to the normal double-stranded structure. It plays crucial roles in viral replication and various molecular biology techniques.
SsRNA: ssRNA (single-stranded RNA) is a type of viral genetic material that consists of a single strand of ribonucleic acid. It is used by various viruses to encode their genetic information and initiate replication within host cells.
Syncytia: Syncytia refer to multinucleated cells formed by the fusion of individual cells. This process is often observed during viral infections, where the virus induces the fusion of host cells, leading to the formation of large, multinucleated structures.
T4 Phage: T4 phage is a type of bacteriophage, a virus that infects and replicates within bacterial cells. It is a lytic phage, meaning it lyses or breaks open the host cell to release new viral particles. T4 phage is a widely studied model organism for understanding viral life cycles and host-virus interactions.
Temperate phages: Temperate phages are a type of bacteriophage capable of both lytic and lysogenic cycles. They can integrate their genome into the host bacterium's DNA, becoming a prophage.
Tissue tropism: Tissue tropism is the specificity of a virus for a particular host tissue, determined by the interaction between viral surface proteins and host cell receptors. This determines which tissues or cell types a virus can infect.
Tobacco Mosaic Virus: Tobacco mosaic virus (TMV) is a plant virus that infects a wide range of plant species, particularly tobacco plants, and is one of the most well-studied and significant viruses in the field of virology. It is an icosahedral, positive-sense, single-stranded RNA virus that serves as a model organism for understanding viral structure, replication, and host-pathogen interactions.
Transduction: Transduction is the process by which genetic material is transferred from one organism to another through the action of a virus or viral vector. This process can have significant implications in the context of viral life cycles, genetic diversity in asexual prokaryotes, genetic engineering, and the development of drug resistance.
Uncoating: Uncoating is the process by which a virus particle sheds its outer protein coat or envelope upon entering a host cell, exposing the viral genome and allowing it to be delivered into the cell's cytoplasm or nucleus for replication.
Varicella-zoster virus: Varicella-zoster virus (VZV) is a highly contagious virus responsible for causing both varicella (chickenpox) and herpes zoster (shingles). It belongs to the Herpesviridae family and establishes lifelong latency in the host.
Varicella-zoster virus: Varicella-zoster virus (VZV) is a member of the Herpesviridae family and the causative agent of two distinct diseases: chickenpox (varicella) and shingles (herpes zoster). It is a DNA virus that establishes a lifelong latent infection in the sensory nerve ganglia of the host after the initial varicella infection.
Viral Envelope: The viral envelope is a lipid-based membrane that surrounds the capsid, or protein shell, of some viruses. This envelope is derived from the host cell's own membrane and is essential for the virus to infect and enter new host cells during the viral life cycle.
Viral Genome: The viral genome refers to the genetic material that encodes the genetic information necessary for a virus to replicate and infect host cells. It is the core of the viral particle and contains the instructions for the virus to hijack the host's cellular machinery to produce new viral particles.
Viral Persistence: Viral persistence refers to the ability of viruses to maintain a long-term presence within a host organism, often without causing overt disease symptoms. This phenomenon is a critical aspect of the viral life cycle, as it allows viruses to evade the host's immune defenses and ensure their own survival and propagation.
Viral Shedding: Viral shedding refers to the release and dissemination of virus particles from an infected host. It is a critical process in the viral life cycle and the transmission of viral infections, particularly in the context of gastrointestinal viral infections.
Viral titer: Viral titer is the concentration of virus particles in a sample, typically expressed as plaque-forming units per milliliter (PFU/mL). It is an essential measure in virology to assess viral infectivity and replication.
Viral Tropism: Viral tropism refers to the specific affinity a virus has for certain host cells or tissues, which determines the sites of viral infection and replication. This concept is crucial in understanding the pathogenesis and tissue tropism of different viruses, as well as their potential for causing disease in various organs and systems.
Virion: A virion is the complete, extracellular, infectious form of a virus. It consists of the viral genome, either DNA or RNA, enclosed within a protective protein coat called a capsid, and in some cases, an additional outer envelope derived from the host cell membrane.
Virulent phages: Virulent phages are a type of bacteriophage that infects bacterial cells and immediately begins the lytic cycle, resulting in the destruction of the host cell. They do not integrate their genetic material into the host DNA.
ZMapp: ZMapp is an experimental biopharmaceutical drug designed to treat Ebola virus infections. It consists of three monoclonal antibodies that target the Ebola virus glycoprotein.