The Position of Viruses in the Biological Spectrum Flashcards
What are viruses?
Viruses are microscopic, acellular agents composed of nucleic acid surrounded by a protein coat
What can viruses infect?
Viruses can infect every type of cell, bacteria, algae, fungi, protozoa, plants, and animals
Who is credited with discovering a “virus”?
Louis Pasteur first postulated that a “living thing” smaller than bacteria can cause diseases when hypothesizing about the origins of rabies
In Latin, what does the term ‘virus’ mean?
Poison
How was the concept of a “filterable virus” discovered?
When fluids from host organisms passed through porcelain filters designed to trap bacteria, the filtrate remained infectious
What was the purpose of filtering these fluids of infected hosts?
The result of the filtrate still contained infectious diseases, proving that a cell-free fluid contained agents that could cause infection
What are obligate intracellular parasites?
Viruses. They cannot multiply unless they invade a specific host cell and must have a host cell for own metabolism
Why are viruses so vital to the evolution of species today?
Viruses have had impacts on the genetic makeup of bacteria, tissues, cells, plants, and animals so they could evolve to their current form
How were animal viruses classified and named?
Animal viruses used to be classified on the basis of their hosts and the disease that they caused
How are viruses named now?
Based on structure, chemical composition, and similarities in genetic makeup
What do viruses lack?
Resemblance to cells and lack any of the protein-synthesizing machinery found in cells
What are the components of a viral structure?
Viruses have repeating subunits which give rise to their crystalline appearance
What are some parts that a virus needs to invade a host cell?
External coating, an inner core with one or more nucleic acid strands of either DNA or RNA, and sometimes one or two enzymes
What do all viruses have?
A caspid
What is a caspid?
A protein shell/coating that surrounds the nucleic acid in the central core
Nucleocapsid
Refers to the capsid and nucleic acid together
What do animal viruses usual possess that is external to the capsid?
An Envelope
What is an envelope of a virus?
An external covering of a nucleocapsid that is a modified piece of the host’s cell membrane
What is the name of viruses that only consist of a nucleocapsid?
A naked virus
What can both naked and enveloped viruses possess on their outer surfaces?
Spikes that project either from the nucleocapsid(naked virus) or the envelope(enveloped virus)
What is the purpose of these spikes?
Spikes allow viruses to dock with the host cells
What is a fully formed virus that is able to establish an infection in the host cell called?
Virion
What are capsids constructed of?
Identical subunits called capsomeres that are composed of identical protein molecules
What is dependent on the capsomeres shape and arrangement when forming the capsid?
The type of capsid orientation(symmetry)
What are the different types of capsid orientations?
Helical(rod-shaped capsomeres), Icosahedral(3D, 20 sided figure with 12 evenly spaced corners), and Complex(non-symmetrical, taking many shapes and are never enveloped)
What is the difference between naked and enveloped helical caspids?
Naked helical viruses are rigid and tightly would into a cylinder while enveloped helical viruses are more flexible
Where can enveloped viruses bud from?
The cell membrane, nuclear envelope, endoplasmic reticulum
What are some characteristics of a complex capsid structure?
They only infect bacteria, may have multiple types of protein, take shapes that are not symmetrical, and are never enveloped
What is a genome?
The sum total of genetic information carried by an organism(chromosomes and genes)
How are viruses different from cells?
Viruses can only have either DNA or RNA in their core and the number of viral genes are quite small
What are some configurations of DNA in viruses?
DNA viruses can be single-stranded(ss), double-stranded(ds), be linear(ds), or circular(ds)
What are some configurations of RNA in viruses?
Double-stranded, most often single-stranded, positive-sense RNA(ready for translation) and negative-sense RNA(must be converted before translation), segmented(own individual genomes)
What is a retrovirus?
A special type of RNA virus that carry their own enzymes to create DNA out of their RNA
What are some other substances found in the virus particle?
Polymerase-synthesize DNA and RNA
Replicases-Copy RNA
Reverse transcriptase(HIV)-synthesizes DNA from RNA
Most viruses lack what?
They completely lack the genes for synthesis of metabolic enzymes. Some viruses feed of the host cells by carrying away their cell’s substances.
The total nucleic acid of a virus can be referred to as the viral ______.
Genome.
What are the general phases in the life cycle of an animal virus?(Lytic cycle)
Adsorption, penetration/uncoating, synthesis, assembly, release
What is the first stage in the Lytic Cycle?
Adsorption- the process of adhering one molecule onto the surface of another one
What are some characteristics of the adsorption phase?
Host range is limited, cells that lack the compatible virus receptors are resistant to adsorption and invasion by the virus
What are tropisms?
Tissue-specific viruses that can only attack certain tissue types in the body
What is the second phase of the animal viral replication cycle?
Penetration and uncoating
What is penetration referring to in the lytic cycle?
Penetration is the process of of viral multiplication in which virus enters the host cell
In what ways can penetration occur to the host cell?
Through endocytosis where the virus is engulfed by the cell and enclosed in a vacuole or vesicle
Through direct fusion with the cell membrane and the nucleocapsid is freed into the cell’s interior
What is the uncoating process of a virus once it attaches to a host cell?
During endocytosis, once the virus penetrates the host cell the enzymes in the vesicle break down the envelope of the virus(if present) or the capsid where the nucleic acid of the virus is freed into the cytoplasm
When does direct fusion occur with the host cell membrane?
With influenza and mumps viruses, when the envelope merges directly with the cell membrane, nucleocapsid is released to the cell’s interior
What is the third process of the lytic cycle?
Synthesis-replication and protein production
How are DNA viruses synthesized in the host cell?
The virus enters the host cells nucleus and are replicated and assembled in the nucleus
How are RNA viruses synthesized in the host cell?
The virus is replicated and assembled in the cytoplasm
What is the major difference between DNA viruses and RNA viruses during the synthesis stage?
DNA viruses are replicated in the nucleus where RNA viruses are replicated in the cytoplasm
What is the fourth step of the lytic cycle?
Assembly-where new viruses are manufactured by the synthesis process
What does the assembly process consist of?
This step puts together the new capsids(protein shell that surrounds nucleic acid) and new nucleic acids to form virus copies
What is the final process of the lytic cycle?
Release-where the virus copies are released from the host cell and go to infect another cell, starting process over again
What are the factors that impact the viruses released by infected cells?
The size of the virus and the health of the host cell
What happens when a mature virus is budded off the membrane of the original host cell?
The mature virus is released into the cytoplasm where it obtains an envelope and spikes
What are cytopathic effects?
Virus-induced damage to a cell that causes change to its microscopic appearance
What are the types of Cytopathic effects?
Inclusion bodies, syncytia, development of intracellular changes, changes in shape and size
What are inclusion bodies?
Damaged cell organelles or compacted viruses in the nucleus and cytoplasm
What is the most common forms of Cytopathic effect?
Syncytia(syncytium) which is the fusion of multiple host cells where the contain multiple nuclei(giant cells)
What are persistent infections?
A cell carries the virus but it is not immediately destroyed(lysed) and can last for a few weeks or remainder of life
What is a provirus?
when viral DNA is incorporated into the DNA of the host cell
Why are proviruses so severe?
They can remain hidden in cells and cause progressive damage and stay in a chronic latent state
When a virus is in a chronic latent state what does the virus do to the host cell?
The virus can go into a period of activation and then inactivation, impacting the host cell for life
Oncogenic viruses are what?
when a virus enters a host cell and alters its genetic material-leads to cancer
Transformation is
the effect on the cell caused by the oncogenic virus
What are bacteriophages?
Viruses that specifically impact bacteria
What are some characteristics of bacteriophage?
Mostly dsDNA, some RNA types exist, bacterial species are infected by specific bacteriophages, make bacteria more pathogenic for humans
What does it mean when a cell lyses?
The cell becomes so full of viruses that it bursts-releasing the mature virion
What are temperate phages(bacteriophages)?
A virus that goes through the adsorption and penetration stages but do not go through the replication and release stages immediately
What is lysogeny?
A condition in which the host chromosome carries viral DNA
What is the prophage state?
Part of a temperate phage process where the viral DNA is inserted into the bacterial chromosomes instead of undergoing viral replication and lysis
What is the process called when a cell becomes activated and progresses into viral replication in a prophage state?
Induction
Why is lysogeny considered less deadly than the lytic cycle?
Lysogeny spreads the virus but does not immediately kill the host, while the lytic cell spreads rapidly infecting many host cells
When a bacterium acquires a new trait from its temperate bacteriophage?
Lysogenic conversion
Eg. Corynebacterium diphtherae – diphtheria toxin
Vibrio cholerae – cholera toxin
Clostridium botulinum – botulinum toxin
What are prions?
A fatal noncellular infectious disease
What are some characteristics of prions?
Composed entirely of altered protein, contain no nucleic acid, cause of chronic diseases in humans/animals
What are some diseases that can be contracted from prions?
Spongiform encephalopathies, Creutzfeldt-Jacob disease, bovine spongiform encephalopathy(BSE)
What are viroids?
An infectious viruslike agent that parasitizes plants but do not have a capsid and are composed of naked strands of RNA
What are three methods which viruses transform a host cell causing cancer?
The virus can alter the cells genetic makeup, the virus can carry the genes that directly cause cancer, or the virus can produce proteins that induce a loss of growth regulation in the cell
How is a prion different than a viroid?
Viroids infect animal cells and bacteria where prions infect plant cells.
Creutzfeldt-Jakob disease and Bovine spongiform encephalopathy are caused by prions. Which of the following best describes a prion?
viral particle
naked DNA
infectious protein
small bacterium
naked RNA
Infectious protein
