Viral Structure and Mechanisms

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Questions and Answers

What is one advantage of enveloped viruses in relation to host cells?

They have a more complex structure.

They are more resistant to antimicrobial agents.

They can easily attach to host cells. (correct)

They are less likely to mutate.

Which of the following describes a disadvantage of enveloped viruses?

They have structures that stabilize them.

They are more enduring to lipid solvents.

They are less adaptable to immune evasion.

They are sensitive to temperature changes. (correct)

What type of virus has a capsid made up of many sides, typically shaped as an icosahedron?

Complex viruses

Polyhedral viruses (correct)

Naked viruses

Helical viruses

Which structure in bacteriophages is responsible for attaching to the host bacterium?

Tail fibers Signup and view all the answers

How do mutations play a role in viral immune evasion?

They can change the structure of the viral surface coat. Signup and view all the answers

What is the primary function of a virus's surface coat?

To facilitate the virus's entry into host cells Signup and view all the answers

Which type of virus is characterized by having additional structures such as a sheath and base plate?

Bacteriophages Signup and view all the answers

What is a defining feature of non-enveloped (naked) helical viruses?

They lack a protective outer envelope. Signup and view all the answers

What primarily triggers an influenza pandemic?

A new strain of influenza virus transmitted from animals to humans Signup and view all the answers

What was a significant factor contributing to the deadliness of the 1918 influenza epidemic?

The rapid onset of symptoms leading to a quick death Signup and view all the answers

What characterizes the cytokine storm associated with the 1918 Influenza?

It leads to excessive inflammation in the lungs Signup and view all the answers

Which of the following is NOT a method for preventing or treating viral diseases?

Using antibiotics to kill the virus Signup and view all the answers

How did changes in amino acids contribute to the H1N1 strain of the 1918 influenza?

They enabled the virus to attach to and invade human lung cells Signup and view all the answers

What is a defining characteristic of poxviruses?

They have multiple membranes surrounding the nucleic acids. Signup and view all the answers

What determines the specificity of a virus to its host cells?

The type of receptor sites on the host surface. Signup and view all the answers

Which suffix is used for viral family names?

-viridae Signup and view all the answers

What aspect does NOT group viruses into families?

Biochemical pathways Signup and view all the answers

How are subspecies of viruses designated?

By numbers following the species name. Signup and view all the answers

Which of the following is true about RNA viruses?

Most RNA viruses have single-stranded RNA. Signup and view all the answers

What type of viral classification comes first when identifying the nucleic acid type?

Whether the genome is RNA or DNA. Signup and view all the answers

Which of the following describes a positive sense single-stranded RNA virus?

Its RNA can directly be translated into proteins. Signup and view all the answers

What is meant by 'antigenic shift' in the context of influenza viruses?

Genetic recombination between different virus strains Signup and view all the answers

Why are pigs considered 'mixing vessels' for influenza viruses?

They facilitate genetic exchange between avian and human viruses. Signup and view all the answers

What is a potential consequence if a hybrid virus is successfully infectious to humans?

Neutralizing antibodies from previous infections may not recognize it. Signup and view all the answers

Which strains of influenza are primarily known to infect humans?

H1, H2, H3 Signup and view all the answers

What are N1 and N2 viral neuraminidases associated with?

Human epidemics Signup and view all the answers

What differentiates an influenza pandemic from seasonal influenza epidemics?

Pandemics have a worldwide spread and high mortality levels. Signup and view all the answers

What historical example is noted as the most serious pandemic in recent history?

1918 Spanish flu Signup and view all the answers

What has been reported regarding Avian influenza A H5N1 and humans?

Several instances of human infections and outbreaks have been reported. Signup and view all the answers

What is the primary characteristic that defines malignant tumors?

They invade neighboring tissues and disrupt normal functions. Signup and view all the answers

Which virus is associated with Burkitt's lymphoma?

Epstein-Barr Virus (EBV) Signup and view all the answers

What criterion is necessary for a virus to potentially cause cancer?

The virus must integrate its DNA into the host cell's chromosomes. Signup and view all the answers

Which of the following is NOT true about viruses and cancer?

All viruses are capable of causing cancer. Signup and view all the answers

What role do hemagglutinin (H) and neuraminidase (N) play in the influenza virus?

They help the virus attach to and release from host cells. Signup and view all the answers

In the context of viral-induced cancer, which statement best describes RNA viruses?

Only retroviruses have oncogenic potential. Signup and view all the answers

Which factor is critical for classifying a virus as oncogenic?

The integration of viral DNA into host cell chromosomes. Signup and view all the answers

What is the significance of viral strains being identified by H and N spikes?

It helps classify them into subtypes. Signup and view all the answers

Study Notes

Enveloped Virus

Envelopes are acquired from the host cell plasma membrane.
Envelopes help the virus evade the host immune system by resembling the host.
They also help the virus fuse with the host cell during invasion.
Envelopes are easily damaged by changes in pH, temperature, and lipid solvents.
Enveloped viruses are more sensitive to antimicrobial agents than naked viruses.

Viral Surface Coat

Viral surface coats help the virus attach to host cells.
Non-enveloped viruses rely on their capsid for attachment while enveloped viruses use their envelope or spikes.
The coat protects the viral nucleic acid from degradation.
Viral nucleic acids encode for the surface coat, which is susceptible to mutations.
Mutations in the viral surface coat allow the virus to evade the host immune system.

Viral Morphology

Viruses are classified based on the shape and structure of their capsid.
There are three main types of capsids: helical, polyhedral, and complex.
Viruses can also be classified as naked or enveloped.

Helical Viruses

Helical viruses have a rod-shaped capsid.
Examples of helical viruses include tobacco mosaic virus (TMV) and influenza virus.
TMV is a naked helical virus while influenza is an enveloped helical virus.

Polyhedral Viruses

Polyhedral viruses have a many-sided capsid.
Most viruses are icosahedral, with 20 triangular faces and 12 corners.
An example of a polyhedral virus is adenovirus.
Poliovirus is a famous example of a naked polyhedral virus.

Complex Viruses

Complex viruses have capsids with additional structures attached.
Bacteriophages have capsids with a sheath, base plate, pins, and tail fibers.
Poxviruses do not have a clear capsid and are surrounded by multiple membranes.

Viral Host Range

Host range refers to the range of host cells a virus can infect.
Viruses are specific, meaning they can only infect certain cells within a single host species.
Specific cells have receptor sites on their surface that the virus can attach to.

Viral Taxonomy

Viruses are grouped into families based on their nucleic acid type, replication strategy, and morphology.
Family names end in "-viridae," for example, Retroviridae.
Genus names end in "-virus," for example, Lentivirus.
Viral species are groups of viruses that share the same genetic information and ecological niche.
Human immunodeficiency virus (HIV) is an example of a viral species.

Nucleic Acid Classification of Viruses

Viruses are classified based on their genetic material (RNA or DNA).
RNA viruses are further classified as double-stranded (dsRNA) or single-stranded (ssRNA).
Single-stranded RNA viruses are either positive (+) sense or negative (-) sense.

Viruses and Cancer

Cancer is uncontrolled, invasive growth of abnormal cells.
Some viruses can cause cancer by integrating their DNA into host cell chromosomes.
Examples of viruses associated with cancer include Epstein-Barr Virus (EBV) and Human Papillomaviruses (HPV).
EBV is associated with Burkitt's lymphoma, a malignant tumor that affects the jaw.
HPV is associated with cervical cancer, oral cancer, and other types of cancer.

How Viruses Cause Cancer

Viruses can alter the genetic material (DNA) of host cells, leading to cancer.
Not all cancers are caused by viruses, and not all viruses can cause cancer.
The ability of a virus to cause cancer depends on its ability to integrate viral DNA into host cell chromosomes.
Retroviruses are the only RNA viruses known to cause cancer.

Influenza

Influenza is an acute respiratory illness caused by an enveloped ssRNA virus.
Influenza symptoms include fever, chills, headache, myalgia, arthralgia, dry cough, rhinitis, sore throat, and ocular symptoms.
Influenza A viruses have Hemagglutinin (H) spikes used for attachment and Neuraminidase (N) spikes used for release.
There are 15 subtypes of H spikes and 9 subtypes of N spikes; strains are identified by their H and N subtypes (ex. H5N1).

Antigenic Shift and Influenza

Antigenic shift refers to changes in the H and N spikes of the influenza virus due to genetic recombination between different strains.
This can lead to new strains of influenza that are not recognized by the host's immune system.
Antigenic shift is a mechanism of immune evasion and can cause pandemics, as seen with the Spanish flu.

Mixing in the Pig

Pigs are considered a “mixing vessel” for influenza viruses.
This is because pigs can be infected with both avian and human influenza viruses.
If genetic exchange occurs between these viruses, a new strain of influenza that can infect humans may emerge.
This could lead to a pandemic if the new strain is unrecognizable to the human immune system.

Influenza Virus Strains

H1, H2, and H3 strains are known to infect humans.
H4, H5, H6, and H7 strains primarily infect animals, particularly swine and poultry.
Recombination of strains has led to the emergence of H5N1 and H7N7 avian influenza viruses that can infect humans.
N1 and N2 neuraminidases are linked to human epidemics.
N3 and N7 neuraminidases are linked to isolated deaths, but not epidemics or pandemics.

Influenza Pandemic

An influenza pandemic is a worldwide epidemic of influenza virus.
Pandemics occur irregularly, with the 1918 Spanish flu being the most serious in recent history.
Pandemics can cause high levels of mortality, with the Spanish flu being responsible for 50-100 million deaths.
Pandemics occur when a new strain of influenza virus is transmitted to humans from animals, especially pigs, chickens, and ducks.
These new strains are unaffected by immunity people have to older human flu strains, so can spread rapidly.

The 1918 Influenza Epidemic: H1N1 Swine Flu

The 1918 influenza pandemic was caused by the deadliest known strain of influenza, H1N1.
It killed 20 million people worldwide, mostly young adults.
Death occurred rapidly, usually within a few hours of symptom onset.
The virus's deadliness was due to a 10 amino acid change that allowed it to attach to, invade, and multiply in lung cells.
This led to a cytokine storm, which is a massive release of cytokines that can cause organ damage.

How to Prevent and Treat Viral Diseases

Good hygiene practices help prevent viral infections, including washing hands frequently and avoiding contact with contaminated food, water, and body fluids.
Vaccines stimulate the body's natural defenses and can help prevent viral infections.
Vaccines are not available for all viruses.
Anti-viral drugs can be used to treat some viral infections, but they are not antibiotics.
Anti-virals can inhibit virus development and/or relieve symptoms.

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Description

This quiz explores the characteristics of enveloped and non-enveloped viruses, focusing on their envelopes, surface coats, and capsid morphology. Understand how these features contribute to viral attachment, evasion of the immune system, and overall stability in varying environments. Test your knowledge on viral classification and structure.