Study Notes: Viral Replication and Animal Viruses in Microbiology

Viral Replication and Animal Viruses

Introduction

This study guide covers essential terminology and concepts related to viral replication, with a focus on animal viruses. Understanding these terms and processes is fundamental for students studying microbiology, especially in the context of virology.

Key Terms in Virology

Definitions and Explanations

• Acellular: Refers to entities, such as viruses, that lack cellular structure and are not composed of cells.

• Bacteriophage (phage): A virus that infects bacteria.

• Capsid: The protein shell that encases the viral genome; provides protection and aids in host cell attachment.

• Nucleocapsid: The combined structure of the viral genome and capsid.

• Complex, helical, polyhedral (icosahedral): Describes the shapes of viral capsids. Helical viruses have rod-shaped capsids; polyhedral (especially icosahedral) viruses have many-sided capsids.

• Productive, latent: Productive infection results in new virus particles; latent infection involves viral genome persistence without immediate production of new viruses.

• Cytopathic effect (CPE): Observable changes in host cells due to viral infection, often leading to cell death.

• DNA virus: Viruses with DNA as their genetic material.

• Envelope: A lipid membrane surrounding some viruses, derived from the host cell membrane.

• Genome: The complete set of genetic material in a virus.

• Segmented: Viral genomes divided into separate pieces, each encoding different proteins.

• Herpesviridae: A family of DNA viruses known for causing herpes infections.

• Immunocompromised: Individuals with weakened immune systems, more susceptible to viral infections.

• Lytic, lysogenic: Lytic cycle leads to host cell destruction; lysogenic cycle involves integration of viral DNA into host genome.

• Nucleic acid: DNA or RNA, the genetic material of viruses.

• Oncogenic, neoplastic: Viruses that can cause cancer (oncogenic) or abnormal tissue growth (neoplastic).

• Papillomaviridae: Family of viruses including human papillomavirus (HPV), associated with warts and cancer.

• Paramyxoviridae: Family of viruses including measles and mumps viruses.

• Picornaviridae: Family of small RNA viruses, such as poliovirus.

• Polio: Disease caused by poliovirus, leading to paralysis.

• Protein folding, denaturing: The process by which proteins achieve their functional shape; denaturing disrupts this structure.

• Retrovirus: RNA viruses that reverse transcribe their RNA into DNA (e.g., HIV).

• Rhinovirus: Virus responsible for the common cold.

• RNA virus: Viruses with RNA as their genetic material.

• Virion: A complete, infectious virus particle.

• Viral life cycle: The sequence of events by which a virus infects a host cell and produces new virions.

• Attachment, entry: Initial steps in viral infection; virus binds to host cell and enters.

• Virus synthesis, assembly, release: Steps in viral replication: making viral components, assembling new virions, and releasing them from the host cell.

• Virus taxonomy: Classification of viruses based on genetic material, structure, and replication strategy.

Major Virus Families and Examples

Overview of Selected Virus Families

• Papillomaviridae: Includes Human papillomavirus (HPV), associated with cervical cancer.

• Paramyxoviridae: Includes Measles virus and Mumps virus.

• Picornaviridae: Includes Poliovirus and Rhinovirus.

• Herpesviridae: Includes Herpes simplex virus and Varicella-zoster virus.

• Retroviridae: Includes Human immunodeficiency virus (HIV).

Viral Replication Cycle

General Steps in Animal Virus Replication

1. Attachment: Virus binds to specific receptors on the host cell surface.

2. Entry: Virus or its genetic material enters the host cell, often via endocytosis or membrane fusion.

3. Uncoating: Viral capsid is removed, releasing the genome into the host cell.

4. Synthesis: Host cell machinery is used to replicate viral nucleic acids and synthesize viral proteins.

5. Assembly: New viral particles are assembled from synthesized components.

6. Release: New virions exit the host cell, often by lysis or budding.

Equation: Viral Growth Rate

The rate of viral replication can be described by:

$\text{Rate} = k[\text{Virus}][\text{Host Cell}]$

where k is the rate constant, and the concentrations of virus and host cell affect the replication rate.

Virus Classification

Criteria for Virus Taxonomy

• Type of nucleic acid: DNA or RNA

• Capsid symmetry: Helical, icosahedral, or complex

• Presence of envelope: Enveloped or non-enveloped

• Host range: Animals, plants, bacteria

• Replication strategy: Lytic, lysogenic, or latent cycles

Table: Comparison of Virus Families

Family	Genome Type	Envelope	Example Virus	Associated Disease
Papillomaviridae	DNA	No	Human papillomavirus (HPV)	Cervical cancer, warts
Paramyxoviridae	RNA	Yes	Measles virus	Measles
Picornaviridae	RNA	No	Poliovirus	Polio
Herpesviridae	DNA	Yes	Herpes simplex virus	Herpes
Retroviridae	RNA (reverse transcribed to DNA)	Yes	HIV	AIDS

Additional Resources

Recommended Study Materials

• Mastering Microbiology Animations: Viral Replication: Animal Viruses (link)

• Replication of Animal Viruses Concept Map: (link)

• Prions Overview: (link)

• Viral Replication YouTube: https://www.youtube.com/watch?v=EqK1CYQvJug

Example: The replication cycle of HIV (a retrovirus) involves reverse transcription of its RNA genome into DNA, integration into the host genome, and eventual production of new virions.

Additional info: Some terms and explanations have been expanded for academic completeness and clarity.