Genetics of Viruses

What are viruses classified as in terms of living organisms?

Viruses are non-living infectious agents or particles.

What are the key characteristics of viruses?

Viruses are non-cellular, have no metabolism, do not maintain homeostasis, and require a host cell to replicate.

What is the role of a host cell in viral replication?

Viruses are obligate intracellular parasites that require a host cell to replicate and express their viral genome.

What happens to a host cell during viral replication?

The host cell may be killed or altered, eventually leading to its death.

What is the structure of the simplest viruses?

Simplest viruses, or naked viruses, consist of a protein coat (capsid) surrounding the nucleic acid (viral genome).

What distinguishes naked viruses from enveloped viruses?

Naked viruses lack a lipid bilayer (envelope), while enveloped viruses have a capsid surrounded by a lipid bilayer.

What types of nucleic acids can be found in viral genomes?

Viral genomes can be ssDNA, dsDNA, ssRNA, or dsRNA.

What is the function of glycoprotein spikes on enveloped viruses?

Spike proteins are used to attach to specific molecules on the host cell.

What is the composition of capsids in viruses?

Capsids are composed of protein subunits called capsomers.

What is the structure of an icosahedron?

An icosahedron has 20 faces, 30 edges, and 12 vertices.

What is the significance of viral attachment in infection?

Viral attachment is crucial for infection; the virus must bind to specific receptors on the host cell.

What determines the host range of a virus?

The host range is related to the virus's ability to attach to receptors on different host species.

What are the mechanisms of viral entry into host cells?

Viral entry can occur through injection of the genome, endocytosis, or fusion with the host cell membrane.

What is the process of un-coating in viral reproduction?

Un-coating is the release of the viral genome into the cytoplasm after the virus enters the host cell.

What is the role of integrase in some viruses?

Integrase catalyzes the insertion of viral DNA into the host DNA, allowing for integration and latency.

What is a lysogenic bacteriophage?

A lysogenic (temperate) bacteriophage integrates its genome into the host DNA, forming a prophage.

How do retroviruses differ from other viruses in their reproductive cycle?

Retroviruses have an RNA genome that is converted to DNA by the reverse transcriptase enzyme.

What is a vector-borne disease?

A vector-borne disease is transmitted by insects, such as yellow fever.

What is zoonosis in the context of viruses?

Zoonosis refers to diseases, like rabies, that are transmitted from animals to humans.

What are arboviruses?

Arboviruses are viruses transmitted by arthropods, particularly insects.

What is tissue specificity in viral infections?

Tissue specificity refers to the ability of a virus to infect specific types of cells based on receptor presence.

What enzyme is used to integrate viral DNA into the host chromosome?

Integrase.

What is a provirus?

A viral genome that has been integrated into the host cell's chromosome.

What are the main steps in the reproductive cycle of a bacteriophage?

1. Attachment to the bacterial cell membrane. 2. Entry of phage DNA into the bacterial cytoplasm. 3. Integration of phage DNA into the bacterial chromosome via integrase. 4. Synthesis of viral components. 5. Viral assembly. 6. Release via cell lysis.

What happens during the release phase of viral reproduction?

The virus can be released through lysis of the host cell or by budding/exocytosis.

How do enveloped viruses typically exit the host cell?

Through budding, where the virus modifies a section of the host cell membrane and pushes out, taking part of the membrane with it.

What is the role of lysozyme in the viral reproductive cycle of bacteriophages?

Lysozyme breaks down the bacterial cell wall, causing lysis and release of new phages.

What is the difference between lytic and lysogenic cycles in bacteriophages?

In the lytic cycle, the phage replicates and causes cell lysis; in the lysogenic cycle, the phage DNA integrates into the host genome and can remain dormant.

What is reverse transcriptase and which viruses utilize it?

Reverse transcriptase is an enzyme that converts viral RNA into DNA; it is utilized by retroviruses like HIV.

What occurs during the entry phase of HIV infection?

The viral envelope fuses with the host cell membrane, releasing the capsid and viral contents into the cytosol.

What is the fate of host cells infected by HIV during exocytosis or budding?

Infected host cells can survive for a while and produce many new viruses.

What is the significance of the integrated provirus in HIV?

The integrated provirus can remain latent for a long time before reactivating to produce new viruses.

What is the process of uncoating in viral infection?

Uncoating is the removal of capsid proteins by cellular enzymes, releasing the viral RNA and enzymes into the cytosol.

What happens to the host chromosomal DNA during the synthesis of viral components in the lytic cycle?

The host chromosomal DNA is degraded.

What is the role of spike glycoproteins in HIV?

They bind to receptors on the host cell plasma membrane, facilitating viral entry.

What is the primary mechanism of release for some animal viruses?

Budding or exocytosis, rather than cell lysis.

What is the outcome of the lysogenic cycle for a host cell?

The host cell can undergo repeated divisions while carrying the integrated prophage.

What is the fate of the host cell after viral assembly in the lytic cycle?

The host cell undergoes lysis, releasing new phages.

What is the role of integrase in retroviruses?

Integrase facilitates the integration of viral DNA into the host cell's chromosome.

How does the release of viruses via exocytosis differ from lysis?

Exocytosis allows the host cell to survive longer while still producing new viruses, while lysis kills the host cell immediately.

What is the significance of the beta 1,4 glycosidic bond in bacterial cells?

It is a bond in peptidoglycan that is broken down by lysozyme, leading to cell lysis.

What is the first step in the reproductive cycle of HIV?

Attachment of spike glycoproteins to host cell receptors.

What happens during the integration step of the bacteriophage reproductive cycle?

Phage DNA integrates into the bacterial chromosome via integrase, leading to a lysogenic state.

What directs the synthesis of viral components in a virus?

Proviral DNA.

What is the role of capsid proteins during viral assembly?

They enclose 2 RNA molecules and molecules of reverse transcriptase and integrase, and assemble with spike glycoproteins during budding.

How do enveloped and naked animal viruses exit the host cell?

Enveloped viruses bud from the plasma membrane, while naked viruses leave through exocytosis.

What is lysogeny in bacteriophages?

A latent state where bacteriophages can integrate their DNA into the bacterial chromosome.

What is a temperate bacteriophage capable of?

Undergoing lytic replication or establishing lysogeny.

What is a lysogen?

A bacterial cell that contains a prophage, which is the integrated DNA of a temperate bacteriophage.

What is a prophage?

The genome of a bacteriophage that has integrated into the bacterial host's DNA or exists as a plasmid.

How can latency be established in human viruses?

Through the integration of the viral genome into host cell DNA (provirus) or as an episome.

What is an episome?

An extrachromosomal element that replicates independently of the host cell chromosome and can integrate into the host chromosome.

Which viruses are known for establishing latency?

Herpes simplex viruses and varicella zoster virus (chicken pox).

What are emerging viruses?

Viruses that have arisen recently or have a greater probability of causing infection, often due to mutations.

Give an example of an emerging virus and its associated disease.

HIV, which causes AIDS.

What are viroids?

Infectious RNA molecules that lack protein and can infect plants.

What are prions?

Infectious proteins that cause fatal neurodegenerative diseases and lack nucleic acid.

What is a characteristic of prions that makes them difficult to inactivate?

They are 'super tough' and almost impossible to inactivate.

Name a neurodegenerative disease caused by prions.

Mad cow disease.

What is the process of prion replication?

Abnormal prion proteins interact with normal prion proteins, converting them into abnormal forms.

What is the incubation time for prion diseases?

Months to years.

What is the effect of prions on brain tissue?

They cause a spongy appearance and destruction of brain tissue.

What is the first step in prion replication?

Abnormal prion protein interacts with normal prion protein.

What happens to normal prion proteins during prion replication?

They are converted to abnormal prion proteins.

What is chronic wasting disease?

A disease of deer characterized by progressive weight loss and is fatal.

What is the significance of the normal prion protein in prion replication?

It must be present for the replication of abnormal prion proteins to occur.