Essential Biology Chapter 10-Viruses and other Noncellular Agents
lysogenic cycle
A phage replication cycle in which the viral genome becomes incorporated into the bacterial host chromosome as a prophage and does not kill the host.
Virus
A tiny, nonliving particle that invades and then reproduces inside a living cell.
lytic cycle
A type of viral (phage) replication cycle resulting in the release of new phages by lysis (and death) of the host cell.
provirus
A viral genome that is permanently inserted into a host genome.
emerging viruses
A virus that has appeared suddenly or has recently come to the attention of medical scientists.
What is a bacteriophage?
A virus that infects bacteria
phages
A virus that infects bacteria; also called a bacteriophage.
What is an adenovirus?
A virus that infects the human respiratory system
List three major outbreaks of emerging viruses from the past 100 years.
AIDS-1981/Ebola 2014-16/West Nile Virus 1996
reverse transcriptase
An enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis.
What do prions do?
Convert normal proteins by folding, changing alpha helix to beta pleated sheet.
Describe an adenovirus
DNA enclosed in a protein coat shaped like a 20-sided polyhedron. At each corner of the polyhedron is a protein spike, which helps the virus attach to a susceptible cell.
True or false: A retrovirus needs reverse transcriptase to make viral DNA from the host-cell RNA. If false, please make it a correct statement.
False, a retrovirus needs reverse transcriptase to make viral DNA from the viral RNA.
Describe a bacteriophage
Has legs with a larger head full of DNA, and a tail to puncture cell membrane.
What are three ways that viruses can get into a plant?
Lesions caused by injuries/transfer by insects that feed on the plant/contaminated farming or gardening tools
Phage infects cell->Phage incorporates into host Genome->Cell divides with Phage DNA passing to daughter cells->Phage DNA is excised from bacterial chromosome->Phage DNA replicates and phage proteins are made.*
Lysogenic Cycle*
A virus in which life cycle can be triggered to enter into the other one? What triggers that event?
Lysogenic to Lytic. External Stressors
Phage infects cell->Phage DNA circularizes, remaining separate from host DNA.->Phage DNA replicates and phage proteins are made.->Cell lyses release phage.*
Lytic Cycle*
What makes prions so unusual as pathogens?
Prions, unlike any other infectious agent, have no nucleic acid (DNA or RNA)
why can RNA viruses mutate so quickly?
RNA has no mechanisms to repair copying errors
Reverses the flow of genetic information ___________
Retrovirus
A molecule that makes DNA from RNA ___________
Reverse transcriptase
Which viral life cycle can be triggered to enter into the other one? What triggers that process?
The lysogenic cycle can be converted into the lytic cycle. Usually, some kind of external stressor can initiate that process.
A human cell has a mutation in a gene, the effect of which is a lack of certain receptor proteins on the surface of the cell. Would a typical enveloped virus be able to infect that cell?
The virus would be stopped from entering that particular cell because the virus would have trouble adhering to the cell.
What is a prion?
an infectious protein
the protein coat of a virus is the
capsid
How do viruses give rise to new diseases?
evolving into more dangerous forms/diseases spreading among hosts/viral diseases from a small isolated population can spread
Describe the influenza virus
has an outer envelope made of phospholipid membrane, with projecting spikes of protein.
Why is infection by herpesvirus permanent?
herpesvirus leaves viral DNA in the nuclei of nerve cells
what decides how much damage a virus causes?
how quickly the immune system responds
HIV
human immunodeficiency virus 1981
Prions
infectious protein particles that do not have a genome
Describe one way that some viruses can perpetuate their genes without immediately destroying the cells they infect.
inserting their DNA into the DNA of the cell they infect
what do most viruses reproduce through
lysogenic cycle
What is a bacteriophage reproductive cycle called?
lytic cycle
A misfolded protein ____________
prion
Double-stranded viral RNA that inserts itself into a host cell's DNA _________
retrovirus
a virologist develops a drug that specifically targets RNA synthesis of the reproductive cycle of an enveloped virus. what effect would this have?
stop assembly of the virus
prophage
the viral DNA that is embedded in the host cell's DNA
What do prions cause?
transmissible spongiform encephalopathies/brain diseases in animals
retrovirus
virus that contains RNA as its genetic information and inserts their DNA copy of a genome (HIV)
Bacteriophage
viruses that infect bacteria