Chapter 16 Questions
How are virsues similar to and different from cells?
Virsuses and cells both contain genetic material and proteins. However, virsuses are smaller than cells and contain no ribosomes or organells. Moreover, virsues do not have a metabolism and they cannot replicate on their own; they must infect a living host cell to replicate.
What determines a virus's host range?
A virsus's host range is determined by the presence of a specific receptor on the host cell.
How do viruses evolve?
Viruses evolve by natural selection. Mutations in viral DNA or RNA create genetic variation; some variants are more sccessful than others at infecting cells and leaving descendants.
What is the source of energy and raw materials for the synthesis of viruses in a host cell?
The source of energy and raw materials is the host cell's ATP and its stores of nucleotides and amino acids.
Describe the five steps in viral replication.
1 - Attachment: Virus adheres to host cell receptor.
2 - Penetraiton: Virus enters the cell.
3 - Synthesis: Multiple copies of the viral genome and proteins are produced by the host cell.
4 - Assembly: The viral genetic information is packaged in a protein coat.
5 - Release: New viruses leave host cell.
What is a lytic infection?
In a lyric infection, the bacteriophage immediately replicates after infecting a bacterium and then bursts out of the host cell, killing in.
How is a lysogenic infection similar to and different from a lytic infection?
A lysogenic infection is similar to a lytic infection in that they both begin with the attachment and penetration steps. In a lytic infection, the remaining steps (synthesis, assembly, and release) occur immediately, destroying the host bacterium. In contrast, a lysogenic bacteriophage inserts its DNA into the host chromosome, where it is carried on into daughter cells. Eventally an environmental change triggers a switch to the lytic pathway, destroying the infected host cell.
How can a person acquire a viral infection?
Viral infections can be acquired by inhaled repiratory droplets or ingesting contaminated food and water. Some viruses are also transmitted by blood trasfusion, sexual contact or contaminated needles.
Which flu symptoms are caused directly by the virus, and which are caused by the human immune response?
The influenza virus kills cells in the repiratory tact, casing cough and sore throat. The immune system attacks the virus with fever and inflammation, which causes body aches.
Describe how HIV replicates in host cells.
After attachment and penetration, the HIV enzyme reverse transcriptase copies the viral RNA to DNA. The viral DNA then insterst itself into the host cell's DNA. New HIV particles are synthesized and assembled inside the host cell and are released by budding. A new virus acquires its envelope from the host cell's membrane as it emerges.
How are viral infections treated and prevented?
Viral infections are difficult to treat, in part because viruses infect living host cells; it is difficult to destroy the virus without also destroying the host cell. A few antiviral drugs do prevent viral replication, but viruses are genetically variable, and new treatments quickly select for resistant varieties. The best weapon for prevention is a vaccine, which builds immunity to a virus before a person is exposed.
How do viruses enter plant cells and spread within a plant?
Viruses often enter plant cells by hitching a ride on the contaminated mouthparts of plant-feeding insects. The viruses spread within the plant via plasmodesmata or in vascular tissue.
What are some symptoms of a viral infection in plants?
Some symptoms include small dead spots, mottled leaves, abnormal growth, or even streaking in some flowers.
How are viroids and prions different from viruses?
All viruses have genetic information and a protein coat. Viroids consist only of RNA and therefore lack a protein coat. Prions are abnormally shaped proteins wiht no genetic information.
How do viroids and prions cause disease?
Viroids interfere with the production of important proteins. An abnormal prion protein "recruits" normal proteins to refold into the abnormal configuration, triggering a chain reaction that results in cell death.
What is the best way to avoid prion diseases?
The best way to avoid prion disease is to keep animal brains and spinal cords out of the human food chain and out of medical products.
How did researchers gather data about SIV infection in wild primates?
The team gathered ape droppings from several sites in Cameroon. They tested each sample for SIV antibodies and extracted genetic material from the sample. The genetic information revealed the ape species that produced the feces and the type of SIV virus (if any) that infected the ape.
A _____ is a nucleic acid (DNA or RNA) in a capsid.
Virus
An _____ derived from the host cell's membrance surrounds some viruses.
Envelope
Many viruses, including some ______ have relatively complex structures.
Bacteriophages
A virus must infect a _____ to reproduce.
A living cell
Are viruses alive?
Viruses are intracellular parasites that most biologists do not consider to be alive.
Scientists classify viruses based on______
The type of genetic material, the shape of the capsi, the presence or absence of an envelope, the replication strategy and the type of disease.
After a virus infects a cell, its host manufactures many copies of ___
The viral proteins and nucleic acids, then assembles these components into new viruses.
The five stages of viral replication within a host cell are
Attachment, Penetration, Synthesis, Assembly, and Release.
In a _________ new viruses are immediately synthesized, assembled and released.
Lytic Infection
In a ______ the virus's nucleic acid replicates along wiht that of a dividing cell without cusing symptoms. The viral DNA may integrate as a prophage into the host chromosome.
Lysogenic Infection
Viruses differ in ___, or the severity of the disease they cause.
Virulence
HIV and some other viruses cause ______, which are dormant inside animal cells.
Latent Infections
Virsues cause disease by ____
killing the infected cells and by stimulating imune responses.
Viruses infect plant cells, then spread via _____
Plasmodesmata
_______ are naked RNA molecules that infect plant cells.
Viroids
A ____ protein can take multiple shapes, at least one of which can cause diseases.
Prion
Which is NOT a feature associated with Viruses?
Cytoplasm
Genetic Information
Protein Coat
Envelope
Cytoplasm
Which of the following is the largest?
HIV
RNA molecule
E. Coli Cell
Human T Cell
Human T Cell
Which of the following characteristics of life does a virus have?
Ribosomes
Evolution
Homeostasis
Growth
Evolution
Although some viruses are complete after the assembly stage, others are not fully ofrmed until they acquire ____ during the release stage.
DNA
RNA
Proteins
The Envelope
The Envelope
Which type of infection is most similar to a lysogenic infection in bacteria?
A lytic infection in bacteria
An influenca infection in humans
A latent infection in animals
A viroid infection in plants
A Latent infection in animals
Which enzyme copies HIV's genetic material, forming DNA?
DNA polmerase from the host cell
Revverse transcriptase from the virus
RNA polymerase from the host cell
Coat protein from the virus
Reverse transcriptase from the virus
The severity of the symptoms associated with a viral inection is related to
The response of the immune system
The type of genetic material in the virus
The number and the types of cells that become infected
Both A and C
Both A and C
What is a prion?
A high wound circle of RNA
A virus that has not yet acquired its envelope
A protein that can aalter the shape of a second protein
The protein associated with a latent virus
A protein that can aalter the shape of a second protein