Viruses and Their Impact on Life

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Questions and Answers

What is the structural appearance of SARS-CoV-2 primarily due to?

Ribosomal proteins

Nucleic acids

Lipids

Glycoproteins (correct)

What percentage of all human cancers is thought to be associated with viral contributions?

30%

10%

20% (correct)

Which of the following is NOT a way in which cancer can develop?

Inherited mutations

Viral gene impact

Exposure to sunlight

Increased exercise (correct)

What is oncogenesis primarily characterized by?

Unregulated cell division Signup and view all the answers

Which gene in Rous Sarcoma Virus (RSV) is identified as essential for oncogenesis?

v-Src Signup and view all the answers

What disrupts normal cell functions leading to uncontrolled cell division in many cases of cancer?

Gene mutations Signup and view all the answers

How do environmental agents contribute to cancer development?

By causing DNA damage Signup and view all the answers

What does v-Src likely interact with to contribute to oncogenesis?

Many host cell proteins Signup and view all the answers

What is the role of the capsid in a virus?

It protects the genetic material of the virus. Signup and view all the answers

What is meant by the term 'tropism' in the context of viruses?

The specific cell types within a host that a virus can infect. Signup and view all the answers

How do viruses replicate their genetic material?

Only when inside a living host cell. Signup and view all the answers

What distinguishes viruses from other forms of life?

Viruses cannot reproduce outside of a living host cell. Signup and view all the answers

Why are viruses considered to be on the boundary of what is considered 'life'?

They have genetic material but lack cellular machinery for replication. Signup and view all the answers

What is the estimated number of viruses present on the planet?

10^31 Signup and view all the answers

What is the function of an envelope in some viruses?

To protect against the host's immune system. Signup and view all the answers

What is the relationship between a virus’s host range and its potential to cause disease?

A narrower host range allows for more severe disease in specific hosts. Signup and view all the answers

What characteristic is notable about the genes of the mimivirus?

It shares 7 of the 67 universal genes Signup and view all the answers

What is the proposed origin of viruses as described?

Viruses are escaped genetic fragments from true organisms Signup and view all the answers

What hypothesis was made regarding the evolution of viruses?

Viruses originated from an ancient fourth domain of life Signup and view all the answers

What does the observation about DNA-replicating enzymes in viruses suggest?

They show no relationship to host cell enzymes Signup and view all the answers

What type of virus is SARS-CoV-2 classified as?

Single-stranded positive RNA virus Signup and view all the answers

How do scientists view the classification of viruses in terms of being 'alive'?

Most biologists argue that viruses should be excluded from life Signup and view all the answers

What enzymes do viruses typically hijack from their hosts?

Essential enzymes for translation and modification Signup and view all the answers

What was shown regarding the evolutionary relation of viral enzymes?

They show closer relation to ancestral enzymes Signup and view all the answers

What distinguishes v-Src from c-Src?

v-Src is a mutant form of c-Src. Signup and view all the answers

What role does the protein p53 play in the cell cycle?

It inhibits cell division in cells with DNA damage. Signup and view all the answers

Which of the following correctly defines an oncogene?

A mutated gene that promotes uncontrolled cell division. Signup and view all the answers

How does HPV contribute to oncogenesis?

By inactivating tumor suppressors like p53. Signup and view all the answers

Which statement about proto-oncogenes is true?

Proto-oncogenes are normal genes that can become cancerous if mutated. Signup and view all the answers

What is the significance of the multiple-mutation model for cancer development?

It suggests that multiple mutations in proto-oncogenes and tumor suppressor genes are necessary. Signup and view all the answers

What type of gene is c-Src classified as?

A proto-oncogene. Signup and view all the answers

Which phase of the cell cycle does the DNA damage checkpoint regulate?

G1 phase. Signup and view all the answers

Study Notes

Viruses, Their Life Cycle, and Cancer

Viruses are microscopic infectious agents containing DNA or RNA as genetic material.
Viral genomes are enclosed within a protein coat called a capsid.
Some viruses have an additional outer envelope containing glycoproteins.
Viruses replicate only within a host cell, using the host's cellular machinery.

The Coronavirus Pandemic

The human population has recently experienced a global pandemic caused by a virus.
In early 2020, cases of COVID-19 reached pandemic levels.
As of April 2024, 7 million people had died worldwide from COVID-19.

Viruses and the Tree of Life

Viruses infect all forms of life, and every living organism has a virus that can infect it.
Estimates suggest there are over 10 million times more viruses than stars in the universe.
Each virus typically infects a few specific species (host range).
Within a host, only a limited number of cell types will be infected by the virus (tropism).

What Are Viruses?

Viruses are on the boundary of what biologists consider "life."
They contain genetic material and are composed of protein capsids.
They cannot replicate and use genetic information outside a living host cell.
The host cell carries out all steps for viral DNA/RNA and viral protein synthesis.
Large viruses have been discovered that possess molecules needed for translation.
Mimivirus is an example of a large virus.

Viruses = Life?

Mimivirus contains 7 of 67 universal genes shared among domains of life.
Mimivirus encodes various proteins needed for translation and protein modification.
Translation factors, tRNAs, and enzymes are also present in mimivirus.
The "relics" of an ancestral protein translation apparatus have been gradually lost through a genome reduction.

Viruses: A Fourth Domain of Life?

Some scientists hypothesize that viruses evolved from a fourth domain of life that has since disappeared.
Viruses are perhaps merely escaped genetic fragments from hijacking genes from true organisms.
Important enzymes in viruses may superficially resemble those of their hosts.
However, DNA-replicating enzymes in viruses often bear no relation to host enzymes.

Virus Classification

Viruses are classified based on their nucleic acid type (DNA or RNA), capsid symmetry (helical, icosahedral, head-and-tail), and presence or absence of an envelope.
Viral genomes vary in size and structure (single-stranded, double-stranded, DNA, RNA)
Baltimore classification classifies viruses based on their genome structure and replication strategy.

Virus Life Cycles

Bacteriophages have a lytic cycle where progeny viruses are assembled, the host cell breaks open, and mature phages are released.
Some bacteriophages have a lysogenic cycle where phage DNA is integrated into the host chromosome, Replication can occur, and the phage DNA is transmitted to progeny.
Non-enveloped viruses adsorb to host cells. then undergo endocytosis. During the endocytosis step, the viral envelope is destroyed or the viral capsid is released
Enveloped viruses have an outer membranous layer that fuses with the host membrane. Viral genomes are released in the cytoplasm and replicated Viral proteins are transcribed and translated, and assembled into new viruses which are released.

Virus Life Cycles: Non-enveloped Viruses (Poliovirus)

Non-enveloped viruses depend on endocytosis.
Viral genomes are released into the cytoplasm.
Replication involves capturing host cellular machinery for genome replication and translation
New viral copies are assembled and released from the cell.

Virus Life Cycles: Enveloped Viruses (HIV or Zikavirus)

Enveloped viruses often fuse with the host membrane.
Viral genomes are released into the cytoplasm.
Replication involves capturing host cellular machinery.
New viral copies are assembled and released from the cell.

Viruses That Cause Cancer

20% of human cancers are linked to viral infections.
Cancer can result from the host's response to the viral infection or from the impact of viral genes on the host cell.
Some viruses insert their genetic information into host chromosomes carrying oncogenes (cancer-causing genes).
Other viruses disrupt the host cell's genes that regulate cell division.

RSV and the v-src Gene

Viral genes can cause oncogenesis (the development of cancer).
v-src, a viral gene in Rous sarcoma virus (RSV), is essential for oncogenesis.
Mutant v-src forms cause proteins to interact with host cell proteins
Normal avian cells carry a gene (c-src) similar to v-src
Sequences of c-src and v-src are different, and the protein function of c-src is different

Oncogenesis

Cancer is a genetic disease involving mutations in genes that control cell growth and division.
Oncogenesis results in tumors
Tumors are composed of rapidly dividing cells that may invade neighboring tissues.
Cancer development can be caused by inherited mutations, DNA damage from environmental agents, or viral infections.

Viruses That Can Cause Cervical Cancer

Certain types of human papillomavirus (HPV) infection can lead to cervical cancer.
HPV integrates its DNA into the host cell DNA, and can cause cancer.

The Cell Cycle

The cell cycle is a regulated process that controls cell growth, DNA synthesis, and cell division.
Interphase (includes G1, S, and G2 phases) is the period where the cell is not actively dividing
M phase (includes mitosis and cytokinesis) is when the cell divides

DNA Damage Checkpoints

Cells have checkpoints to monitor for DNA damage to prevent errors
p53 is a protein activated by DNA damage that inhibits the cell cycle.

HPV Encodes Tumor Suppressors

HPV E6/7 proteins bind and inactivate the p53 tumor suppressor.
This allows cells with damaged DNA to divide, which can lead to oncogenesis.

Proto-oncogenes and Tumor Suppressors

Proto-oncogenes are normal genes that can become oncogenes (cancer-causing genes) upon mutation.
Tumor suppressors are genes that control cell division,
Mutations in tumor suppressors can lead to uncontrolled cell growth.

Multiple-Mutation Model for Cancer Development

Most human cancers develop from the accumulation of mutations in proto-oncogenes or tumor suppressor genes.
Mutations can lead to benign or metastatic cancer depending on the number and type of mutations.

Take-home Thoughts

The study of viruses and virus-induced cancers deepens our understanding of cellular mechanisms.
Viruses demonstrate varied integration into the tree of life, challenging traditional definitions.

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Description

This quiz explores the fascinating world of viruses, their life cycles, and their role in events like the coronavirus pandemic. It also delves into how viruses interact with living organisms and their vast presence in the environment. Test your knowledge on these microscopic agents and their significant impact on life.