Virus, Viroid, Prion Flashcards
Chapter 1
What is the role of early viral proteins?
Enzymes and regulatory molecules for genome replication.
What are viruses made of?
A strand of genetic material (DNA or RNA) within a protective protein coat called a capsid.
Why are viruses considered nonliving?
They cannot replicate or survive independently without a host.
What are capsomeres?
Structural units that form the capsid of a virus.
What types of symmetry can viral capsids have?
Helical, icosahedral, or complex.
How do viruses replicate?
By infecting a host cell and using its machinery to produce new virions.
What are the five stages of viral replication?
Recognition and attachment, penetration, uncoating, genome replication, and assembly of new particles.
Recognition and Attachment
The virus recognizes and binds to specific receptor molecules on the surface of a susceptible host cell
Example of recognition and attachment
HIV binds to CD4 receptors on T-helper cells
Penetration
The virus enters the host cell through one of the following mechanisms
Direct fusion
Endocytosis
Injection
Penetration: Injection
The viral envelope fuses with the host membrane, releasing the viral genome into the cytoplasm. (e.g., HIV)
Penetration: Endocytosis
The host cell engulfs the virus into a vesicle, which then releases the viral genome into the cytoplasm. (e.g., influenza virus)
Penetration: Injection
The virus injects its genetic material directly into the host cell, leaving the capsid outside. (e.g., bacteriophages)
Uncoating
Cell enzymes from lysosomes enter the cell cytoplasm, removing the virus protein coat and making the viral genome accessible for the next stage.
DNA viruses
Typically replicate in the nucleus using host DNA polymerase. (e.g., herpesviruses)
Replication (Biosynthesis)
The virus hijacks the host cell’s machinery to synthesize viral components.
Replication (Biosynthesis): DNA Viruses
Typically, it replicates in the nucleus using host DNA polymerase. (e.g., herpesviruses)
Replication (Biosynthesis): RNA viruses
Usually replicate in the cytoplasm using viral RNA-dependent RNA polymerase. (e.g., coronaviruses)
Assembly (Maturation)
Once sufficient viral components are synthesized, Viral genomes are packaged into newly synthesized capsids and structural proteins are arranged accordingly.
. Release
Involves the exit of newly formed virions from the host cell:
Lytic viruses
Budding viruses
Release: Lytic viruses
Cause cell lysis, breaking the host cell open and releasing virions. (e.g., bacteriophages, poliovirus)
Release: Budding viruses
Exit without immediately killing the host, taking part of the host membrane as an envelope. (e.g., influenza, HIV)
What is reverse transcription?
A process where retroviruses use reverse transcriptase to convert RNA into DNA.
What are helical viruses?
Viruses with capsids arranged in a spiral, forming a rod-like structure.
What are icosahedral viruses?
Viruses with a 20-sided capsid structure.
What are complex viruses?
Viruses with capsids that are neither helical nor icosahedral, often with additional structures like tails.
What are phages?
Viruses that infect bacteria.
What are enveloped viruses?
Viruses surrounded by a lipid bilayer derived from the host cell.
Why are enveloped viruses vulnerable to detergents?
Detergents disrupt the lipid envelope, inactivating the virus.
What are viroids?
A plant pathogen the comprise only of ssRNA, with no protein coat
Prions
A self-replicating particle that is responsible for a range of neurodegenerative disorders in humans e.g. Creutzfeldt-Jakob disease.
How do Prions replicate
Prions may be altered versions of normal animal proteins, and somehow have the ability to cause the normal version to refold itself into the mutant
What are pseudovirions?
Host-cell DNA fragments encapsulated in a viral capsid, unable to replicate.
Artififcially constructed virus used for study in a lab, contain a viral envolope that enbales the to simulate infection
What are defective viruses?
Viruses with a defective nucleic acid require a helper virus to replicate.
Hepatitis D Virus is a defective virus that requires Hepatitis B Virus (HBV) as its helper virus. HDV lacks the envelope proteins needed to form infectious virions. Instead, HDV uses the envelope proteins produced by HBV to form new virus-like particles and facilitate its transmission.
Does the DNA of the virus integrate into the host DNA in the lytic cycle
No, the DNA of the virus doesn’t integrate into the host DNA in the lytic cycle.
Does the DNA of the virus integrate into the host DNA in the lysogenic cycle?
Yes, the DNA of the virus integrates into the host DNA in the lysogenic cycle.
What happens to the host DNA in the lytic cycle?
he host DNA is hydrolyzed (broken down) in the lytic cycle.
hat happens to the host DNA in the lysogenic cycle?
: The host DNA is not hydrolyzed in the lysogenic cycle.
Is there a prophage stage in the lytic cycle?
No, there is an absence of a prophage stage in the lytic cycle.
Is there a prophage stage in the lysogenic cycle?
Yes, the lysogenic cycle includes a prophage stage where viral DNA integrates with the host DNA.
How does viral DNA replication occur in the lytic cycle?
In the lytic cycle, DNA replication of the virus takes place independently of the host DNA replication.
How does viral DNA replication occur in the lysogenic cycle?
In the lysogenic cycle, DNA replication of the virus takes place along with the host DNA replication.
Are symptoms of viral replication evident in the lytic cycle?
Yes, symptoms of viral replication are evident in the lytic cycle.
Are symptoms of viral replication evident in the lysogenic cycle?
No, symptoms of viral replication are not evident in the lysogenic cycle.
What is a prophage stage?
The dormant phase of a virus during where the viral genome is integrates into the host’s DNA
