Chapter 6

Q: Why is there debate on whether viruses are alive?

A: They lack independent metabolism and cannot reproduce alone.

Q: How are viruses best described instead of “living” or “dead”?

A: Active or inactive.

Q: How have viruses influenced evolution?

A: By integrating their genetic material into host genomes.

Q: What percentage of the human genome is made up of ancient viral sequences?

A: 8%.

Q: What is horizontal gene transfer, and how do viruses contribute?

A: The transfer of genes across species, facilitated by viruses.

Q: Can viruses enter the nucleus?

A: Yes.

Flashcards: Early Discoveries of Viruses

Q: Who discovered the first evidence of viruses?

A: Ivanowsky & Beijerinck.

Q: What does it mean that viruses are “filterable”?

A: They can pass through filters designed to trap bacteria.

Q: How did electron microscopy (1950s) impact virology?

A: Allowed scientists to visualize viruses for the first time.

Q: Who discovered foot-and-mouth disease as a viral infection?

A: Loeffler & Frosch.

Q: How do viruses compare in size to bacteria?

A: They range from 20 nm to 1000 nm, making them ultramicroscopic.

Q: What was Louis Pasteur’s contribution to virology?

A: He hypothesized rabies was caused by an infectious agent smaller than bacteria and coined the term “virus.”

Flashcards: Virus Structure - Geometric Perfection

Q: What is a capsid?

A: A protective protein shell surrounding viral nucleic acid.

Q: What types of nucleic acid can viruses have?

A: DNA or RNA, double-stranded or single-stranded.

Q: What is a viral envelope?

A: A lipid membrane with spikes for host attachment.

Q: How do viruses attach to specific hosts?

A: Through specific molecules (spikes, surface proteins) binding to cell receptors.

Q: What receptor does SARS-CoV-2 bind to in human cells?

A: ACE2 receptors.

Q: What are the three main virus shapes?

A: Helical, Icosahedral, and Complex (Bacteriophage).

Q: How do bacteriophages impact the ocean ecosystem?

A: They destroy up to 40% of oceanic bacteria daily, affecting food chains and nutrient cycles.

Flashcards: Virus Replication - The Factory Process

Q: Why must viruses infect a host cell?

A: They cannot replicate on their own.

Q: What are the five stages of viral replication?

A: Attachment, Penetration, Replication, Assembly, Release.

Q: What is the lytic cycle?

A: Rapid viral replication, destroying the host cell.

Q: What is the lysogenic cycle?

A: Viral DNA integrates into the host genome and remains dormant.

Q: How do retroviruses (e.g., HIV) replicate?

A: They use reverse transcriptase to integrate into the host genome.

Q: What is viral latency?

A: When a virus integrates into host DNA and remains inactive until triggered.

Q: Give an example of a latent virus.

A: Varicella-zoster virus (chickenpox → reactivates as shingles).

Q: What does reverse transcriptase do?

A: Converts viral RNA into DNA.

Q: What does integrase do?

A: Inserts viral DNA into the host genome.

Flashcards: Bacterial Defense Mechanisms Against Viruses

Q: What do restriction enzymes do?

A: Cut viral DNA before infection takes over.

Q: What is the CRISPR system?

A: A genetic immune system in bacteria that fights viruses.

Q: How does CRISPR protect bacteria?

A: By storing viral DNA fragments and using them to recognize and cut future infections.

Q: How is CRISPR used in biotechnology?

A: For gene editing and potential cures for genetic diseases.

Flashcards: Emerging Viral Diseases

Q: What is genome mixing (reassortment)?

A: When two viruses infect the same cell and swap genetic material.

Q: How do mutations affect viruses?

A: Small genetic changes lead to new variants.

Q: What is zoonotic transmission?

A: When viruses jump from animals to humans.

Q: How does climate change impact viral spread?

A: Warmer temperatures expand mosquito and tick ranges, increasing disease transmission.

Q: What caused the H1N1 (Swine Flu) pandemic?

A: Genetic reassortment between pig, bird, and human flu viruses.

Flashcards: Viruses & Cancer - Oncogenic Viruses

Q: What are oncogenes?

A: Genes that, when inserted by viruses, can cause cancer.

Q: How do viruses promote tumor growth?

A: By disabling tumor suppressor genes.

Q: What virus causes cervical cancer?

A: HPV.

Q: What virus is linked to Burkitt’s lymphoma?

A: Epstein-Barr Virus (EBV).

Q: What viruses cause liver cancer?

A: Hepatitis B & C (HBV, HCV).

Q: How are viruses used in cancer treatment?

A: Modified viruses can target and destroy cancer cells.

Q: What breakthrough occurred in 2018 with virotherapy?

A: A modified polio virus increased survival rates in glioblastoma patients.

Flashcards: Viroids & Prions – Virus-Like Agents

Q: What is the main structural difference between viruses, viroids, and prions?

A:

• Viruses: DNA/RNA + protein coat

• Viroids: RNA only

• Prions: Protein only

Q: What do viroids infect?

A: Plants.

Q: What do prions infect?

A: Animals and humans.

Q: What are viroids?

A: Small infectious RNA particles with no protein coat.

Q: Give an example of a viroid disease.

A: Potato spindle tuber disease.

Q: What are prions?

A: Infectious misfolded proteins.

Q: What diseases do prions cause?

A: Mad Cow Disease, Creutzfeldt-Jakob Disease (CJD).

Q: Can prions be destroyed easily?

A: No, they are highly resistant.

Flashcards: Key Takeaways for Exam Preparation

Q: Are viruses considered living?

A: No, but they direct life processes.

Q: What are some viral replication strategies?

A: Lytic, lysogenic, and retroviral cycles.

Q: How do bacteria defend against viruses?

A: CRISPR and restriction enzymes.

Q: What are oncogenic viruses?

A: Viruses that can trigger cancer.

Q: How do emerging viruses develop?

A: Through mutation, genome mixing, and zoonotic transmission.