Viruses

Answer: A. A virus that requires transport to the nucleus in order to produce viral proteins likely requires use of nuclear RNA polymerase in order to create mRNA that can be translated to protein. Therefore, only DNA viruses need to be transported to the nucleus to produce viral proteins, eliminating everything but (A).

After infection of a cell, a viral particle must transport itself to the nucleus in order to produce viral proteins. What is the likely genomic content of the virus? A. Double-stranded DNA B. Double-stranded RNA C. Positive-sense RNA D. Negative-sense RNA

Non-enveloped viruses will persist longer on the surface of objects. The envelope on viruses are very sensitive to heat, detergents, and dessication, meaning enveloped viruses are easier to sterilize/kill than non-enveloped viruses.

Are enveloped or non-enveloped viruses more likely to persist on the surface of objects?

Yes, they can infect humans, such as in the case of hepatitus D.

Are viroids able to infect humans?

Answer: Yes Adaptation to an environment does not have to be present immediately, but can occur over a period of time. Viruses can mutate, meaning they are able to adapt to their environment over time.

Are viruses able to adapt to their environment? Explain your reasoning.

Answer: No Virus uses host cells to create new viruses, meaning each virion is created in its fully formed state and will not grow any further in size or complexity.

Are viruses able to grow? Explain your reasoning.

Answer: No Viruses do not have membrane-bound organelles or cytoplasm like prokaryotes or eukaryotes, thus they are unable to maintain homeostasis.

Are viruses able to maintain homeostasis? Explain your reasoning.

Answer: Yes and No Viruses are able to multiply, but they require a host in order to create virions. So viruses are able to reproduce, but they cannot reproduce alone, they need a host.

Are viruses able to reproduce? Explain your reasoning.

Answer: Unknown Not enough research has been put in to determine if viruses can react to a stimulus.

Are viruses able to respond to stimuli? Explain your reasoning.

It is best to think of viruses as robots, they do not meet the requirements to be considered living, but they are still able to function, so they are not considered nonliving; however, most would consider viruses more nonliving than living.

Are viruses considered living organisms?

1. Virus enters the cell; inside the cell, the capsid of the virus dissolved in a process called uncoating, causing the RNA in the capsid to be released. 2. Reverse transcriptase from the retrovirus binds to the RNA of the retrovirus, and reverse transcribes the RNA to form a complimentary DNA (cDNA) strand; reverse transcriptase will then transcribe the new strand of cDNA to produce another strand of cDNA, the two cDNA strands will then come together to form a double-stranded DNA molecule. 3. Integrase from the retrovirus will then remove the 5' and 3' ends from the DNA; by removing them, the DNA will form sticky ends that allows it to be integrated into the host's DNA. Meanwhile, the viral RNA molecule gets degraded by the host's ribonuclease. 4. Viral DNA integrates into the host's DNA and enters a provirus stage like in the lysogenic cycle. Unlike the lysogenic cycle, the viral DNA will not have any repressors that will prevent expression of the viral genome (not dormant/latent). 5. Viral DNA is then transcribed at the same time as host's DNA, which causes the formation of viral mRNA; the viral mRNA will exit the nucleus and get translated by cytosolic ribosomes to form the components of the virus. 6. The viral components are then assembled into new virions, but are immature viruses without an envelope. The virions will obtain an envelope by budding off of the cell in a vesicle from the cell membrane. 7. Protease from the retrovirus will cleave the other two enzymes in the virus to make sure that they are fully functional before the virus enters another cell and infects it.

Describe the life cycle of a retrovirus.

-When virus enters a cell, the genetic material of the of the virus integrates with the host's genetic material. -The genetic material of the virus uses its repressor genes to repress the expression of those genes when integrated to the host's genome. -The virus will not initiate replication until a stimulus is initiated on the cell, like heat or light. -While the virus is latent, the cell will divide, which will lead to the replication of the virus's genetic material into the daughter cells. The genetic material of the virus will be found in the daughter cells of each division. -Virus will stay dormant until it is acted on by a stimulus, like UV light, radiation, or chemicals; at that point, the virus's repressor genes will be weaken, activating the virus's genome, and causes the virus to enter the lytic cycle.

Describe the lysogenic cycle.

-When the virus enters the cell, it immediately begins using the machinery in the cell to start making copies of the virus's genetic material. -Viruses are assembled, and soon causes the cell to lyse when there are too many virions produced for the cell to contain. -When the cell lyses, the virions will then go on to infect other cells.

Describe the lytic cycle.

Answer: Yes Viruses have genes made up of nucleic acids and a capsid made of smaller subunits called capsomeres, thus they have different levels of organization through these smaller building blocks forming a larger product.

Do viruses have different levels of organization? Explain your reasoning.

Answer: Yes and No It takes energy to form new viruses, but the energy needed for replication is provided by the host. So while yes, viruses do use energy for reproduction, they do not produce the energy themselves.

Do viruses use energy for processes? Explain your reasoning.

Answer: C. Viruses can exist in either the lytic or lysogenic cycle; they may even switch between them. During the lytic cycle, the virus's DNA takes control of the host cell's genetic machinery, manufacturing numerous progeny. In the end, the host cell bursts (lyses) and releases new virions, each capable of infecting other cells. In the lysogenic cycle, viral DNA is added to the host cell's genome, where it can remain dormant for days or years. Either spontaneously or as a result of environmental circumstances, the provirus can reactivate and enter the lytic cycle. Thus, (A) and (B) are incorrect because the terms are reversed. (D) describes features of bacteriophages, which are viruses that infect bacteria - not the human nervous system. (C) accurately describes how HSV operates during the lysogenic cycle, making it the correct answer.

Herpes simplex virus (HSV) enters the human body and remains dormant in the nervous system until it produces an outbreak after exposure to heat, radiation, or other stimuli. Which of the following statements correctly describes HSV? A. While it remains dormant in the nervous system, the virus is in its lytic cycle. B. During an outbreak, the virus is in the lysogenic cycle. C. HSV adds its genetic information to the genetic information of the cell. D. HSV contains a tail sheath and tail fibers.

Bacteriophages uses a sheath that they can use to inject their genetic information into a bacteria.

How are bacteriophages able to enter a bacterial cell?

Through receptor-mediated endocytosis and direct fusion Only through receptor-mediated endocytosis

How are enveloped viruses able to enter a eukaryotic cell? How are non-enveloped viruses able to enter a eukaryotic cell?

Normal proteins are typically in the shape of an α-helix, while prion proteins are typically in the shape of a β-sheet. When a prion protein comes into contact with a normal protein, the normal protein's conformation is converted from an α-helix to a β-sheet. When more α-helices are converted to β-sheets, it leads to protein deposits aggregating. This build up can lead to interference with biological processes, and lead to decay of organs.

How do prions infect other organisms?

When viroids bind to large numbers of RNA sequences, it can silence genes in the cell's genome. This results in the prevention of the synthesis of necessary proteins, resulting in metabolic and structural damage.

How do viroids infect a host?

Alone, hepatitus D cannot do anything, but when coinfected with hepatitus B, hepatitus D is able to exert a silencing effect on human hepatocytes.

How does hepatitus D viroids affect humans?

Individual virions will only contain one type of nucleic acid.

How many types of genetic material are viruses allowed to have?

Helical

Identify what shape the virus shown is.

Polyhedral/Isohedral

Identify what shape the virus shown is.

Spherical

Identify what shape the virus shown is.

It would be less likely to be infected by another bacteriophage.

If a bacterium is infected by a bacteriophage, is it more likely or less likely to be infected by another bacteriophage (superinfection)?

Yes. Antibiotics are used to target parts of bacteria in hopes of killing them, but you cannot kill viruses if they are not living. Instead of destroying the virus, antiviral medicines try to shut off the viral replication cycle.

If viruses are not alive, does that affect how we deal with a viral infection?

Answer: C. Prions are infectious proteins that cause misfoldings of other proteins. Prions generally cause a shift towards β-sheet conformations, causing decreased solubility and increased resistance to degradation. This mechanism is very similar to the one described here for Alzheimer's disease, making (C) the correct answer.

In Alzheimer's disease, a protein called the amyloid precursor protein (APP) is cleaved to form a protein called β-amyloid. This protein has a β-sheet structure and precipitates to form plaques in the brain. This mechanism of disease is most similar to which of the following pathogens? A. Bacteria B. Viruses C. Prions D. Viroids

A. Nucleic acid B. Capsid C. Sheath D. Tail Fibers

Name the labeled structures of the bacteriophage.

The most advantageous method would be viral extrusion. The other two methods involves the death of the host cell, which would mean it would no longer be used for the reproduction of viruses. Viral extrusion leaves the host cell alive, meaning it can continue to be used for viral replication.

Of the three methods of virions being released from the host, which method is most advantageous for the virus?

Viroid & Prion Virus Prokaryotic Cell Eukaryotic Cell

Order the following from smallest to largest: Virus Eukaryotic cell Prokaryotic cell Viroid & Prion

The description indicates that the virus contains an outer layer of phospholipids with an inner capsid, meaning it can enter a host via direct fusion. Within the capsid, there is single-stranded RNA that can be immediately translated to proteins by the ribosomes of the host cell.

The coronavirus, which causes the common cold, is described as an enveloped, single-stranded positive-sense RNA virus. What does this indicate about the virus?

-Viruses cannot make their own ATP -Viruses cannot reproduce on their own -Viruses do not contain any organelles -Not made up of cells (acellular)

What are some characteristics of a virus that makes it a nonliving infectious agent?

Bovine Spongiform Encephalopathy (Mad Cow Disease) Creutzfeldt-Jakob Disease Familial Fatal Insomnia

What are some diseases caused by prions?

Size Shape Genetic Material Type of Host

What are the 4 characteristics that determines a virus's type?

-Capsid -Nucleic acid -Envelope (sometimes)

What are the components that make up a virus?

1. Living things must maintain homeostasis 2. Living things must have different levels of organization 3. Living things must reproduce 4. Living things must grow 5. Living things use energy 6. Living things respond to stimuli 7. Living things adapt to their environment

What are the seven criteria that something needs to meet in order to be considered a living organism?

1. Viral invasion initiates cell death. 2. Cell lyses as a result of extremely large numbers or virions produced. 3. Viral extrusion: The virus buds off of the host cell through forming a vesicle from the plasma membrane of the host, resulting in leaving the host alive.

What are the three methods of how virions are released from a host cell?

-Reverse transcriptase -Integrase -Protease

What are the three types of enzymes that are found in the capsid of a retrovirus?

Isohedral/Polyhedral Helical Spherical

What are the three types of shapes of viruses that infect eukaryotic cells?

Lytic cycle Lysogenic cycle

What are the two different patterns of viral replication?

1. Receptor-mediated endocytosis 2. Direct fusion

What are the two methods for a virus to infect a eukaryotic cell?

Positive-sense Negative-sense

What are the two types of single-stranded RNAs that can be found in viruses?

Viroids and Prions

What are the two types of subviral particles?

Hepatitus D

What disease in humans are caused by viroids?

It means that a virus needs a host in order to reproduce, and end up causing harm to the host cell.

What does it mean for a virus to be an obligate intracellular parasite?

There are bacteria-sized viruses called mamaviruses. These giant viruses has smaller viruses associated with it. When a mamavirus infects an amoebae, it creates a giant virus factory, which will be hijacked by the smaller viruses.

What happens if a virus infects another virus?

Normal proteins will be converted from α-helices to β-sheets, which will lead to protein deposits in the brain. The protein deposits will be cleaned up in the brain, but the aftermath will leave cavities in the place where the protein deposits were. This can lead to loss of certain brain functions and even to symptoms of certain diseases, like dementia.

What happens if prions infect the brain?

To inject genetic material of the virus into the bacterium.

What is the function of the sheath on bacteriophages?

To anchor itself to the membrane of the bacterium when injecting genetic material.

What is the function of the tail fibers on bacteriophages?

Retroviruses

What is the one type of virus that does not undergo either the lytic or lysogenic cycles?

RNA replicase, which allows the viral RNA to be replicated in order to form capsomers.

What kind of enzyme does a negative sense RNA virus need to carry in order to reproduce?

Capsomers

What kind of proteins make up the capsid of a virus?

Prions are only made up of proteins, meaning they do not have any genetic material.

What makes prions unique compared to viroids and viruses?

Spherical viruses are actually either polyhedral/isohedral or helical viruses surrounded by an envelope. They are considered spherical because of the phospholipid envelope surrounding them.

What makes spherical viruses unique compared to the other two viral shapes?

The capsomers on the virus's capsid determines its antigenicity.

What part of a virus determines its antigenicity?

Dormant/Latent

What term is used to describe a virus in the lysogenic cycle?

Virulent

What term is used to describe a virus in the lytic cycle?

β-sheets

What type of conformation are prions typically?

Single-stranded RNA Single-stranded DNA Double-stranded RNA Double-stranded DNA

What types of nucleic acid may be present in a virus?

Infected indefinitely Kill the infected cell

When a retrovirus integrates its genetic material into the host's cell genome, it allows the cell to be ____________________________________. Meaning the only way to remove the infection is to ________________________________________.

In its capsid.

Where is the genetic material of a virus stored?

Answer: D. In a virus, the nucleic acid can either be DNA or RNA and - in both cases - can either be single- or double-stranded. Therefore, all of the types of nucleic acids listed here could be used for a viral genome, making (D) the correct answer.

Which of the following types of nucleic acid could form the genome of a virus? I. Single-Stranded RNA II. Double-Stranded DNA III. Single-Stranded DNA A. I only B. II only C. I and II only D. I, II, and III

Plants

Which type of organisms do viroids typically infect?

HIV is a type of retrovirus. Retroviruses have an enzyme known as reverse transcriptase, which allows the virus to transcribe its RNA into cDNA. However, the reverse transcriptase will frequently make mistakes in the coding of cDNA from RNA, leading to many mutations to develop for the retrovirus. A drug that may have worked for a previous generation of HIV may not work for the next generation of HIV due to mutations caused by reverse transcriptase.

Why is it hard for a vaccine to be developed for HIV?

Nucleocapsid

___________________ is the term used for a capsid that has a nucleic acid in it.

Capsid

____________________ is the outer protein coat of a virus.

Uncoating

____________________ is the process of a virus's capsid being dissolved in a cell, causing the release of its genetic material.

Prions

_____________________ are proteinaceous infectious particles, or subviral particles made up of proteins.

Viroids

_____________________ are subviral particles that are made up of a single strand of circular RNA.

Virions

______________________ are individual virus particles.

Direct fusion

______________________ is the method for a virus to enter a eukaryotic cell by fusing their envelope to the cell membrane as if it were a vesicle; this allows the virus to be released into the cell once the envelope fuses.

Subviral particles

_______________________ are molecules that are smaller than viruses and are able to cause infections in organisms. They are categorized as nonliving infectious agents.

Antigenicity

_______________________ refers to the part of the substance that stimulates the activity of white blood cells.

Lytic cycle

________________________ is the replication process for viruses where replication immediately begins, resulting in the death of the host cycle.

Prophage/Provirus

________________________ is the viral DNA that is embedded in the host cell's DNA.

Catalytic RNA

_________________________ are RNA molecules that can make or break covalent bonds, viroids are considered to be this type of RNA.

Bacteriophage

_________________________ are viruses that infects bacteria only.

Receptor-mediated endocytosis

_________________________ is the method for a virus to enter a eukaryotic cell by binding to a receptor on the cell membrane, which causes the virus to be encased in a vesicle and taken into the cell.

Envelope

__________________________ is the phospholipid bilayer that surrounds the capsid of a virus. Not all viruses have this structure.

Negative sense RNA Virus

_________________________________ is a single stranded RNA virus whose genetic material must be replicated to synthesize a complimentary RNA strand before it can be translated by ribosomes in the host's cell.

Positive sense RNA Virus

____________________________________ is a single stranded RNA virus whose genetic material can be directly translated into capsomeres by the ribosomes in the host's cell.