Biology 121: Viruses Powerpoint
Both bacter and archaea can protect themselves from viral infection with the _____.
CRISPR-Cas system
Particular nuclease proteins interact with the CRISPR REGION; these are called _____.
CRISPR-associated (Cas) proteins
The resulting RNA's are cut into pieces and bound by ____.
Cas proteins
What does CRISPR stand for?
Clustered Regulary Interspaced Short Palindromic Repeats
RNA polymerase transcribes the proviral ______.
DNA into RNA molecuels
Viruses are classified as ____.
DNA viruses or RNA viruses
The ______ is one of several emerging viruses that cause hemorrhagic fever, an often fatal illness.
Ebola virus
When does a cell begin to manufacture viral proteins?
Once a viral genome has entered a cell
______ use reverse transcriptase to copy their RNA genome into DNA.
Retroviruses
_______ are all caused by prions.
Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans
What does tabacco mosaic disease do?
Stunts the growth of tabacco plants and gives their leaves a mosaic coloration.
Viral infections cannot ______.
be treated by antibiotics
There is controversy about whether the largest virus evolved ______.
before or after cells
Capsids are built from protein subunits called:
capsomeres
Every time the host divides, it ______.
copies the phage DNA and passes the copies to daughter cells
Bacteria have their own ____ against phages.
defenses
Viruses do not fit our _____.
definition of living organisms
Some viruses cause infected cells to produce toxins that lead to _______.
disease symptoms
Others have molecular components such as ________.
envelope proteins that are toxic
The virus makes use of host ______.
enzymes, ribosomes, tRNA's, amino acids, ATP, and other molecules
The relationship between phage and bacteria is in constant _____.
evolutionaly flux
It is possible that ______ may allow mosquitoes that carry viruses to expand their range.
global climate change
Many plant viruses have a _______, while others have an icosahedral capsid.
helical capsid
A capsid can have a variety of structures; associated viruses may be referred to as _____.
helical or icosahedral viruses
A global epidemic is called a ______.
pandemic
The lysogenic cycle replicates the _____.
phage genome without destroying the host
The lytic cycle is a _____.
phage replicative cycle that culminates in the death of the host cell
The viral envelope is usually derived from the host cell's ______.
plasma membrane as the viral capsids exit
Vaccines can _____.
prevent certain viral illnesses
Smaller, less complex entities called ______ also cause disease in plants and animals respectively.
prions
Since viruses can replicate only within cells, they _____.
probably evolved as bits of cellular nucleic acid
The intograted viral DNA is known as a _____.
prophage
The largest virus discovered's genome encodes _____.
proteins involved in translation, DNA repair, protein folding, and polysaccharide synthesis
The viral DNA that is integrated into the host genome is called a ____.
provirus
Natural selection favors bacterial mutants with surface proteins that cannot be _____.
recognized as receptors by a particular type of phage
Viruses cannot _____.
reproduce or carry out metabolism outisde of a host cell
Foreign DNA can be identified as such and cut up by cellular enzymes called _____.
restriction enzymes
The bacterium's own DNA is protected from the ______ by being methylated.
restriction enzymes
Viral nucleic acid molecules and capsomeres spontaneously _____.
self-assemble into new viruses
The genome of a virus is either a _____.
single linear or circular molecule of the nucleic acid
Viral glycoproteins on the envelope bind to ______.
specific receptor molecules on the surface of a host cell
H1N1 is the ______.
strain that caused the 2009 flu pandemic
Viral envelopes (derived from membranes of host cells) ______.
surround the capsids of influenza viruses and many other viruses found in animals
The RNA mlecules function both as mRNA for _______.
synthesis of viral proteins and as genomes for new virus particles released from the cell
Phages that use both the lytic and lysogenic cycles are called ______.
temperate phages
Other examples of emerging viruses include ______.
the chikungunya virus and the Zika virus (2015)
Flu epidemics are caused by ______; these infect a wide variety of animals including birds, pigs, horses, and humans
type A influenza viruses
In the late 1800's, researches hypothesized that _____ might be responsible for tobacco mosaic disease.
unusually small bacteria
The viral genome enters the host cell in a _____.
variety of ways
Viral envelopes contain a combination of ____.
viral and host cell molecules
A phage that reproduces only by the lytic cycle is called a _____.
virulent phage
Bacteriophages (phages):
viruses that infect bacteria
There are two key variable used to classify viruses that infect animals:
-an RNA or DNA genome, either single or double stranded -the presence or absence of a membranous envelope
Viral genomes may consist of either:
-double or single stranded DNA -double or single stranded RNA
Bacteriophages have an ______ that encloses their DNA.
enlonated capsid head
A vaccine is a ________.
harmless derivative of pathogenic microbes that stimulate the immune system to mount defenses against that harmful pathogen
Candidates for the source of viral genomes include ______.
plasmids and transposons
Strains of influenza A are given ______ based on the viral surface proteins hemagglutinin (HA) an neuraminidase (NA).
standardized names
The Cas protiens use the phage-related RNA to target _____.
the invading phage DNA
______, it can block any attempt of the same type of phage to reinfect it.
If the cell survives the infection
Some viruses have _____ that help them infect hosts.
accessory structures
When a phage infects a bacterial cell that has the CRISPR-Cas system, the pahge DNA _____.
is integrated between two repeat sequences
Later work suggested that the infectious agent did ______.
not share features with bacteria (such as the ability to grow on nutrient media)
Other viral membranes form from the host's ______ and are then replaces by an envelope made form Golgi apparatus membrane
nuclear envelope
A virus is a very small infectious particle consisting of _____.
nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope
Viruses exist in a shady area between life-forms and chemicals, leading a kind of ______.
"borrowed life"
What are the two major routes that plant viruses spread?
1. Horizontal transmission, entering through damaged cell walls 2. Vertical transmission, inheriting the virus from a parent
What three processes contribute to the emergence of new viral diseases?
1. RNA viruses have an unusually high rate of mutation 2. The disease can be disseminated from a small, isolated human population and can eventually spread around the world 3. About three-quarters of new human diseases originate by spreading to humans from animals
More than _______ types of viral diseases of plants are known and cause spots on leaves and fruits, stunted growth, and damaged flower or roots.
2,000
Viruses have between ____ genes in their genome.
3-2,000
HIV (human immunodeficiency virus) is the retrovirus that causes _____.
AIDS (acquired immunodeficiency syndrome)
Prions might also be involved in diseases such as _______.
Alzheimer's and Parkinson's disease
The largest virus yet discovered is the size of _____.
a small bacterium
Unlike a prophage, a provirus remains _____.
a permanent resident of the host cell
Each "spacer" sequence between the repeats corresponds to DNA from ____.
a phage that had infected the cell
Several prions _______ that can convert more proteins to prions.
aggregate into a complex
Most plant viruses have _____.
an RNA genome
What is a virus?
an infectious particle consisting of genes packaged in a protein coat.
In 2009, a general outbreak (epidemic) of a flu-like illness appeared in Mexico and the United States, caused by ______.
an influenza virus names H1N1
Each virus has a _____, which is a limited number of host cells that it can infect.
host range
Diseases caused by viral infections affect _______.
humans, agricultural crops, and livestock worldwide
New roads into a remote area may ______.
increase spread of viral diseases
Changes in host behavior or the environment can _______.
increase the spread of viruses responsible for emerging diseases
The broadest variety of RNA genomes is found in viruses that ______.
infect animals
Prions are _______.
infectious proteins that appear to cause degenerative brain diseases in animals
A protein tail piece attaches the phage to the host and _____.
injects the phage DNA inside
The use of _______ may help prevent the spread.
insecticides and mosquito nets
Viruses were detected indirectly ______.
long before they were actually seen
The lytic cycleproduces new phages and ______.
lyses (breaks open) the host's cell wall, releasing the progeny viruses
Many viruses that infect animals have ____.
membranous envelopes
Plasmids, transposons, and viruses are all _____.
mobile genetic elements
Viruses are _____.
much simpler in structure than even prokaryotic cells
Phages have two alternative reproductive mechanisms which are _____.
the lytic cycle and the lysogenic cycle
Prions are somehow able to convert a normal form of the protein into _____.
the misfolded version
A capsid is _____.
the protein shell that encloses the viral genome
An environmental signal can trigger _____ and switch to the lytic mode.
the virus genome to exit the bacterial chromosome
Viruses are obligate intracellular parasites, which means _____.
they can replicate only within a host cell
Emerging viruses are _____.
those that suddenly become apparent
The attempt of the pahge to infect the cell triggers _____.
transcription of the CRISPR region
Prions are incorrectly folded proteins, and can be _______.
transmitted in food, act slowly, and are virtually indestructible
Antiviral drugs can help to _______, viral infections by inhibiting synthesis of viral DNA and by interfering with viral assembly.
treat, not cure
The phage DNA is _____.
cut and destroyed
Whereas few bacteriophages have an envelope or an RNA genome, many animal viruses have _____.
both
Naturally selection favors phage mutants that ____.
can bind to altered cell surface receptors or that are resistant to enzymes
Viruses may damage or kill cells by ______.
causing the release of hydrolytic enzymes from lysosomes
In 1935, Wendell Stanley _____.
crystallized the infectious particle, now known as tobacco mosaic virus (TMV)
