Lecture Notes: Viruses

Introduction

• Lecture presented by Amoeba Sisters
• Topic: Viruses
• Contact: Twitter (@AmoebaSisters) and Facebook

The Common Cold

• Caused by a virus (not treatable with antibiotics)
• Symptoms: Sneezing, coughing, general malaise

What Are Viruses?

• Not cells; not classified as living things, but debate exists
• Antibiotics target bacteria (living cells) not viruses
• Anti-fungal medications target fungi (living cells) not viruses
• Cannot classify viruses as prokaryotes or eukaryotes

Virus Structure

• Much smaller than cells; need electron microscope to see
• Varied shapes (e.g., bacteriophage)
• All viruses have genetic material (DNA or RNA)
• Have protein coat (capsid) protecting genetic material
• May have additional structures (enzymes, outer envelope)

Virus Replication

• Require a host to replicate
• Hosts provide necessary machinery for replication
• Very specific regarding host

Types of Viral Replication Cycles

1. Lytic Cycle

• Virus attaches to host cell (binds to receptor)
• Injects genetic material (DNA or RNA)
• Host follows viral instructions, makes virus copies
• Host cell membrane ruptures (lysis), releasing new viruses

2. Lysogenic Cycle

• Virus genetic material hides in host’s genetic material
• Host replicates its own and viral genetic material
• Viral genetic material can be in daughter cells
• Trigger can switch lysogenic cycle to lytic cycle
  • Example triggers: Chemical triggers, lack of food

Specific Viruses: HIV

• HIV can lead to AIDS
• Binds to CD4 glycoprotein on Helper T cells
  • Helper T cells are crucial for immune system
• Medications exist to slow HIV replication
• Continuous research on preventing virus attachment
• Mutation of viruses complicates treatment (e.g., HIV)

Positive Aspects of Viruses

• Useful in gene therapy
• Target pest insects as an alternative to chemical pesticides (e.g., Nuclear Polyhedrosis Virus)
• Consideration needed for ecological consequences of viral pesticides

Conclusion

• Summary: Viruses are unique, with specific replication needs and cycles
• Stay curious! (Amoeba Sisters)