Chapter 6

What is the debate regarding whether viruses are alive?

Viruses lack independent metabolism and cannot reproduce alone.

What alternative terms do we use to describe viruses instead of 'living' or 'dead'?

Active or inactive.

What impact have viruses had on evolution?

Viruses have integrated their genetic material into host genomes.

What percentage of the human genome consists of ancient viral sequences?

8%.

What is horizontal gene transfer? How do viruses contribute to it?

The transfer of genes across species, facilitated by viruses.

Can viruses enter the host cell nucleus?

Yes.

Who discovered the first evidence of viruses?

Ivanowsky & Beijerinck.

What does it mean for viruses to be 'filterable'?

They can pass through filters designed to trap bacteria.

How did electron microscopy impact the study of viruses?

It allowed scientists to visualize viruses for the first time.

Who linked foot-and-mouth disease to a viral infection?

Loeffler & Frosch.

How do viruses compare in size to bacteria?

Viruses range from 20 nm to 1000 nm, making them ultramicroscopic.

What was Louis Pasteur's contribution to virology?

He hypothesized that rabies was caused by an infectious agent smaller than bacteria and coined the term 'virus'.

What is a capsid in viruses?

A protective protein shell surrounding viral nucleic acid.

What types of nucleic acids can viruses have?

DNA or RNA, which can be double-stranded or single-stranded.

What is a viral envelope?

A lipid membrane with spikes that help in host attachment.

How do viruses attach to their specific hosts?

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

What receptor does the SARS-CoV-2 virus bind to in human cells?

ACE2 receptors.

What are the three main shapes of viruses?

Helical, Icosahedral, and Complex (Bacteriophage).

How do bacteriophages affect the ocean ecosystem?

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

Why must viruses infect a host cell for replication?

They cannot replicate on their own.

What are the five stages of viral replication?

Attachment, Penetration, Replication, Assembly, Release.

What is the lytic cycle of viral replication?

A process of rapid viral replication that destroys the host cell.

What occurs during the lysogenic cycle?

Viral DNA integrates into the host genome and remains dormant.

How do retroviruses like HIV replicate?

They use reverse transcriptase to integrate into the host genome.

What is viral latency?

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

Can you give an example of a latent virus?

Varicella-zoster virus, which can reactivate as shingles.

What function does reverse transcriptase serve in viruses?

It converts viral RNA into DNA.

What role does integrase play in the viral life cycle?

It inserts viral DNA into the host genome.

What do restriction enzymes do in bacterial defense against viruses?

They cut viral DNA before infection can take over.

What is the CRISPR system?

A genetic immune system in bacteria that fights viruses.

How does CRISPR protect bacteria from viruses?

By storing viral DNA fragments to recognize and cut future infections.

How is CRISPR utilized in biotechnology?

For gene editing and potential cures for genetic diseases.

What is genome mixing (reassortment) in viruses?

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

What effect do mutations have on viruses?

They lead to small genetic changes which can result in new variants.

What is zoonotic transmission?

When viruses jump from animals to humans.

How does climate change affect the spread of viruses?

Warmer temperatures expand ranges of mosquitos and ticks, increasing disease transmission.

What was the cause of the H1N1 (Swine Flu) pandemic?

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

What are oncogenes?

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

How do viruses promote tumor growth?

By disabling tumor suppressor genes.

Which virus is linked to cervical cancer?

Human Papillomavirus (HPV).

Which virus is associated with Burkitt's lymphoma?

Epstein-Barr Virus (EBV).

Which viruses are known to cause liver cancer?

Hepatitis B & C viruses (HBV, HCV).

How are viruses being used in cancer treatment?

Modified viruses can target and destroy cancer cells.

What breakthrough occurred in 2018 with virotherapy?

A modified polio virus increased survival rates in glioblastoma patients.

What is the key structural difference between viruses, viroids, and prions?

Viruses: DNA/RNA + protein coat; Viroids: RNA only; Prions: Protein only.

What do viroids infect?

Plants.

What do prions infect?

Animals and humans.

What are viroids?

Small infectious RNA particles that have no protein coat.

Can you provide an example of a viroid disease?

Potato spindle tuber disease.

What are prions?

Infectious misfolded proteins.

What diseases can prions cause?

Mad Cow Disease and Creutzfeldt-Jakob Disease (CJD).

Can prions be easily destroyed?

No, they are highly resistant.

Are viruses classified as living organisms?

No, viruses are not considered living, but they can direct life processes.

What are some strategies used for viral replication?

Lytic, lysogenic, and retroviral cycles.

How do bacteria defend against viral infections?

Through mechanisms like CRISPR and restriction enzymes.

What are oncogenic viruses?

Viruses that can trigger cancer.

How do emerging viruses develop?

Through mechanisms such as mutation, genome mixing, and zoonotic transmission.