Viruses
62 flashcards covering Viruses for the MCAT Biology & Biochemistry section.
Viruses are microscopic infectious particles that aren't considered living organisms because they lack cells and can't reproduce on their own. They consist of genetic material—either DNA or RNA—surrounded by a protein coat, and sometimes an outer lipid envelope. Viruses invade host cells, hijacking their machinery to replicate and spread, which can lead to diseases like the flu or COVID-19. Understanding viruses is crucial in biology as they illustrate key concepts in genetics, evolution, and immunology.
On the MCAT, viruses often feature in biology and biochemistry questions, such as multiple-choice items on their structure, replication processes, or interactions with the immune system. You'll need to differentiate between lytic and lysogenic cycles, and avoid common traps like confusing viruses with bacteria or overlooking their role in genetic diversity. Focus on topics like viral entry mechanisms, mutation rates, and vaccine development, as these tie into passages and experiments. Always memorize key examples, like bacteriophages, to tackle application-based questions effectively.
Terms (62)
- 01
Virus
A virus is a non-cellular infectious agent that requires a host cell to replicate, consisting of genetic material enclosed in a protein coat.
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Capsid
The capsid is the protective protein shell surrounding the genetic material of a virus, determining its shape and aiding in attachment to host cells.
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Viral envelope
The viral envelope is a lipid bilayer derived from the host cell membrane, surrounding some viruses and containing embedded viral proteins for host interaction.
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Viral nucleic acid
Viral nucleic acid is the genetic material of a virus, which can be DNA or RNA, single-stranded or double-stranded, and serves as the blueprint for viral replication.
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Bacteriophage
A bacteriophage is a virus that infects and replicates within bacteria, often using a lytic or lysogenic cycle to destroy or integrate into the host genome.
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Lytic cycle
The lytic cycle is a viral replication process where the virus infects a host cell, replicates its genetic material, assembles new virions, and causes the cell to burst, releasing progeny viruses.
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Lysogenic cycle
The lysogenic cycle is a viral replication strategy where the viral genome integrates into the host cell's DNA and replicates along with it without immediately killing the cell.
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Viral attachment
Viral attachment is the initial step in infection where viral proteins bind to specific receptors on the host cell surface, determining the virus's host range.
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Viral entry
Viral entry occurs when a virus penetrates the host cell membrane, either by fusion, endocytosis, or injection of its genetic material, to initiate replication.
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Uncoating
Uncoating is the process in viral replication where the capsid is removed, releasing the viral genetic material into the host cell's cytoplasm or nucleus.
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Viral replication
Viral replication is the process by which a virus uses the host cell's machinery to copy its genetic material and produce viral proteins for assembling new virions.
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Reverse transcriptase
Reverse transcriptase is an enzyme found in retroviruses that synthesizes DNA from an RNA template, allowing the viral genome to integrate into the host DNA.
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Retrovirus
A retrovirus is an RNA virus that uses reverse transcriptase to convert its RNA genome into DNA, which then integrates into the host genome for replication.
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Host range
Host range refers to the variety of host species or cell types that a virus can infect, determined by the compatibility of viral attachment proteins and host receptors.
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Viral tropism
Viral tropism is the preference of a virus for specific host tissues or cell types, based on receptor availability and cellular factors required for replication.
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Antigenic drift
Antigenic drift is the gradual accumulation of mutations in viral surface proteins, leading to minor changes that allow the virus to evade the host immune response.
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Antigenic shift
Antigenic shift is the sudden reassortment of genetic material between different viral strains, resulting in major changes that can lead to new pandemics.
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Interferon
Interferon is a protein produced by host cells in response to viral infection, signaling nearby cells to activate antiviral defenses and inhibit viral replication.
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Immune evasion by viruses
Immune evasion by viruses involves strategies like hiding in host cells, mutating surface proteins, or inhibiting immune signaling to avoid detection and destruction by the immune system.
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Vaccination against viruses
Vaccination against viruses introduces a harmless form of the virus or its components to stimulate an immune response, providing long-term protection against future infections.
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Attenuated vaccine
An attenuated vaccine uses a weakened live virus to mimic natural infection, eliciting a strong and lasting immune response with minimal risk of disease.
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Inactivated vaccine
An inactivated vaccine contains killed viruses that cannot replicate, stimulating an immune response without causing infection.
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Subunit vaccine
A subunit vaccine uses specific viral proteins or fragments, rather than the whole virus, to trigger an immune response while avoiding potential side effects.
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Antiviral drugs
Antiviral drugs are medications that inhibit viral replication by targeting specific viral enzymes or processes, such as reverse transcriptase or viral uncoating.
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HIV life cycle
The HIV life cycle involves attachment to CD4 receptors, entry into host cells, reverse transcription of RNA to DNA, integration into the host genome, and production of new virions.
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Influenza virus
Influenza virus is an RNA virus that causes seasonal flu, featuring segmented genomes that enable antigenic shift and rapid mutation.
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Herpes virus
Herpes virus is a DNA virus that establishes latent infections in neurons, reactivating periodically to cause outbreaks like cold sores or shingles.
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Acute viral infection
An acute viral infection is a short-term illness where the virus replicates rapidly, causes symptoms, and is typically cleared by the immune system.
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Chronic viral infection
A chronic viral infection persists over time, with the virus evading immune clearance and potentially leading to long-term health issues like liver damage from hepatitis.
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Viral latency
Viral latency is a state where the virus remains dormant in the host cell, integrated into the genome or hidden in the nucleus, without producing new virions until reactivated.
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Oncogenic viruses
Oncogenic viruses are viruses that can cause cancer by integrating their genetic material into the host DNA, disrupting normal cell growth regulation.
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Viral mutations
Viral mutations are changes in the viral genome due to errors in replication, allowing viruses to adapt quickly and potentially evade immune responses.
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Recombination in viruses
Recombination in viruses occurs when genetic material from two different viral strains mixes, creating new variants with combined traits.
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Horizontal gene transfer via viruses
Horizontal gene transfer via viruses happens when viruses carry and insert host genes between organisms, contributing to genetic diversity.
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Persistent infection
A persistent infection is a long-term viral presence in the host, where the virus continuously replicates at low levels without causing acute symptoms.
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Viral zoonoses
Viral zoonoses are diseases transmitted from animals to humans, such as Ebola or COVID-19, often requiring adaptation for human-to-human spread.
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Baltimore classification
The Baltimore classification system categorizes viruses based on their genetic material and replication strategy, grouping them into seven classes from double-stranded DNA to positive-sense RNA.
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DNA viruses
DNA viruses use DNA as their genetic material and typically replicate in the host nucleus, including viruses like herpes and adenoviruses.
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RNA viruses
RNA viruses use RNA as their genetic material, replicating in the cytoplasm or nucleus, and include types like positive-sense, negative-sense, and retroviruses.
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Viral assembly
Viral assembly is the process where newly synthesized viral components, such as proteins and nucleic acids, come together to form mature virions inside the host cell.
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Viral release
Viral release occurs when mature virions exit the host cell, either by cell lysis in the lytic cycle or budding in enveloped viruses, spreading infection.
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Common trap: Viruses are alive
Viruses are not considered living organisms because they lack cellular structure, metabolism, and the ability to replicate independently outside a host cell.
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Strategy for preventing viral spread
Preventing viral spread involves hygiene practices, vaccination, and isolation measures to break transmission chains and reduce host exposure.
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R0 of viruses
R0, or basic reproduction number, measures the average number of secondary infections from one infected individual in a susceptible population, indicating a virus's potential to spread.
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Pandemic vs. epidemic
A pandemic is a widespread outbreak of a disease across multiple countries or continents, while an epidemic is a sudden increase in cases within a specific region.
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Interferon response
The interferon response is a host defense mechanism where infected cells release interferons to induce an antiviral state in neighboring cells, limiting viral spread.
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Viral proteases
Viral proteases are enzymes that cleave viral polyproteins into functional proteins, essential for replication and a common target for antiviral drugs.
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Quasispecies in viruses
Quasispecies refer to the diverse population of related viral variants generated by high mutation rates, allowing viruses to adapt rapidly to host environments.
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Viral vectors in gene therapy
Viral vectors are modified viruses used in gene therapy to deliver therapeutic genes into host cells, exploiting their natural ability to enter and integrate genetic material.
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Phage therapy
Phage therapy uses bacteriophages to treat bacterial infections by specifically infecting and lysing pathogenic bacteria, offering an alternative to antibiotics.
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Viral inclusion bodies
Viral inclusion bodies are aggregates of viral particles or proteins within infected host cells, visible under a microscope and indicative of infection.
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Hemagglutination by viruses
Hemagglutination is the clumping of red blood cells caused by certain viruses, used in diagnostic tests to detect viral presence.
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Viral oncogenes
Viral oncogenes are genes carried by certain viruses that can transform host cells into cancerous ones by altering growth signaling pathways.
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Neutralizing antibodies
Neutralizing antibodies are immune proteins that bind to viral surface proteins, preventing the virus from attaching to and entering host cells.
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Viral egress
Viral egress is the exit of newly formed virions from the host cell, often involving budding for enveloped viruses or lysis for non-enveloped ones.
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Co-infection of viruses
Co-infection occurs when a host cell is infected by more than one virus strain simultaneously, potentially leading to genetic recombination and new variants.
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Viral serotypes
Viral serotypes are distinct variations of a virus identified by their antigenic properties, requiring specific immune responses for each type.
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Example: Poliovirus replication
Poliovirus, an RNA virus, enters host cells via receptor binding, translates its RNA directly into proteins, replicates in the cytoplasm, and causes cell lysis to release new virions.
This leads to paralysis in severe cases by destroying motor neurons.
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Viral persistence mechanisms
Viral persistence mechanisms include latency, immune suppression, or integration into the host genome, allowing viruses to evade clearance and establish long-term infections.
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Defective interfering particles
Defective interfering particles are incomplete viral genomes that interfere with the replication of standard viruses, potentially reducing the severity of infection.
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Viral envelope glycoproteins
Viral envelope glycoproteins are proteins embedded in the viral membrane that mediate attachment and fusion with host cells, crucial for entry.
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Strategy: Identifying viral infections
Identifying viral infections often involves serological tests, PCR for genetic material, or observing cytopathic effects in cell cultures.