BIOL 1202 Ch. 19
Viruses exist in a shady area between life-forms and chemicals, leading a king of ________________________.
"borrowed life"
Restriction enzymes act as what?
"molecular scissors"
Number of cuts made in DNA will depend on number of times the ________________ sequence occurs
"target"
There are two key variables used to classify viruses that infect animals:
1. An RNA or DNA genome, either single stranded or double stranded 2. The presence or absence of a membranous envelope
Phages have 2 alternative reproductive mechanisms:
1. Lytic cycle 2. Lysogenic cycle
What are the three processes that contribute to the mergence of new viral diseases:
1. RNA viruses have an usually high rate of mutaiton 2. The disease can be disseminated from a small, isolated human population and spread worldwide 3. About three-quarters of new human diseases originated by spreading to humans from animals
Viral genomes may consist of two types:
1. double-or single-stranded DNA 2. double- or single-stranded RNA
Viruses have between __________________ genes in their genome.
3-2,000
What piece attaches the phage to the host and injects the phage DNA inside?
A protein tail piece
What types of drugs can help to treat, not cure, viral infections by inhibiting synthesis of viral DNA and by interfering with viral assembly?
Antiviral drugs
are also called phages, are viruses that infect bacteria
Bacteriophages
What are examples of pandemics:
Black Death, Spanish flu, HIV/AIDS
are but from protein subunits called capsomeres
Capsids
What are two other examples of emerging viruses other than Ebola.
Chikungunya virus and recently Zika virus (2015)
What is the CRISPR-Cas System represented by?
Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs)
What is a palindromic sequence?
DNA sequence that is the same when read either 5' to 3' or 3' to 5'. DNA is double stranded, so base pairs must be read not just the bases on one strand to see if a sequence is palindromic. (a): Example of palindromic sequence 5′-G G A T C C-3′ 3′-C C T A G G-5′
Viruses are classified as what two types?
DNA virus or RNA virus
one of several emerging viruses that cause hemorrhagic fever, and often fatal illness
Ebola virus
Viruses that suddenly become apparent
Emerging viruses
Is either a single linear or circular molecule of the nucleic acid
Genome
Other viral membranes form from the host's nuclear envelope and are then replaced by an envelope made from what membrane?
Golgi apparatus membrane
What strain caused the 2009 flu pandemic?
H1N1
the retrovirus that causes AIDS (acquired immunofrifiency syndrome)
HIV (human immunodeficiency virus)
What was the largest virus discovered to date is the size of a small bacterium, 1.3 MB dsDNA genome, capsid 440 nm
Megavirus chilensis
Are viruses alive?
No
Are viruses cells?
No
What are the best understood of all viruses?
Phages
Candidates for the source of viral genomes include what?
Plasmids and transposons
transcribes the proviral DNA to RNA
RNA polymerase
are nucleases that cut double stranded DNA at specific nucleotide-sequences
Restriction enzymes
use reverse transcriptase to copy their RNA genome into DNA
Retroviruses
stunts growth of tobacco plants, gives their leaves a mosaic coloration
Tobacco mosaic disease (TMV)
(derived from membranes of host cells) surround the capsids of influenza viruses and many other viruses found in animals
Viral envelopes
In 1935, who confirmed this latter hypothesis by crystallizing the infectious particle, now known as tobacco mosaic virus (TMV)?
Wendell Stanley
What is the controversy about virus evolution?
Whether viruses evolved before or after cells
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 were detected indirectly long before they were
actually seen
Flu epidemics are caused by type A influenza viruses; infect:
birds, pigs, horses, and humans
the protein shell surrounding the viral genome
capside
Since viruses can replicate only within cells, they probably evolved as bits of what?
cellular nucleic acid
The viral DNA molecule is incorporated into the host cell's ______________________.
chromosomes
Bacteriophages have what that encloses their DNA?
elongated capsid
A disease that exists permanently in a particular region or population
endemic
Whereas few few bacteriophages have an ____________________ or an ______ _____________, many animal viruses have both
envelope; RNA genome
What can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode?
environmental signal
a widespread occurrence of an infectious disease in a community at a particular time
epidemic
What is an example of an epidemic?
flu-like illness caused by the influenza virus H1N1 that appeared in Mexico and the US in 2009
Viral ________________________ on the envelope bind to specific receptor molecules on the surface of a host cell
glycoproteins
A capsid can have a variety of structures; they may be referred to as ____________________ or ________________ viruses
helical; icosahedral
What do viruses make use of?
host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules
Every virus has this, a limited number of host cells it can infect
host range
Diseases caused by viral infection affects:
humans, agricultural crops, and livestock worldwide
Viruses may damage or kill cells by causing the release of what?
hydrolytic enzymes from lysosomes
The viral genome enters the host cell:
in many ways
Some viruses have accessory structures that help them:
infect hosts
replicates the phage genome without destroying the host
lysogenic cycle
is a phage replicative cycle that culminates in the death of the host cells
lytic cycle
What is an example of an endemic:
malaria in Africa and Chicken pox in the US
Once the viral genome has entered a cell, the cell begins to:
manufacture viral proteins
Many viruses that infect animals have a:
membranous envelope
The bacterium's own DNA is protected from the restriction enzymes by being ___________________, preventing cuts
methylated
Plasmids, transposons, and viruses are all what?
mobile genetic elements
Viral nucleic acid molecules and capsomeres spontaneously self-assemble into what?
new viruses
Can viral infections be treated by antibiotics?
no
Can you get the flu from getting the yearly flu shot?
no
Do viruses fit our definition of living organisms?
no
Is the flu vaccine 100% effective?
no
Is there a link between vaccines and autism?
no
Later work suggested that the infectious agent in TMV did not share features with bacteria (i.e. inability to grow on what?)
nutrient media
A global epidemic
pandemic
Unlike a prophage, a provirus remains a __________________ resident of the host cell.
permanent
Smaller, less complex entities that also cause disease in plants and animals, respectively
prions
The lytic cycle produces new phages and lyses the host's cell wall, realizing what?
progeny viruses
The integrated viral DNA is known as what?
prophage
Natural selection favors bacterial mutants with surface __________________ that cannot be recognized as receptors by a particular type of phage
proteins
Strains of influenza A are given standardized names based on the viral surface ______________ hemagglutinin (HA) and neuraminidase (NA)
proteins
The viral DNA that is integrated into the host genome
provirus
Is cross-species transmission (CST) or spillover common or rare in viruses?
rare
What can viruses not do?
reproduce or carry out metabolism outside of a host cell
Foreign DNA can be identified as such and cut up by cellular enzymes called ___________________ ____________________.
restriction enzymes (RE)
cleave DNA molecules at specific base sequences
restriction enzymes (RE)
In the late 1800s, researches hypothesized that what might be responsible for Tobacco mosaic disease?
small bacteria
Diseases that are seen only occasionally, and usually without geographic concentration
sporadic
Phages that use both the lytic and lysogenic cycles
temperate phages
What are examples of sporadic disease?
tetanus, rabies, and typhoid fever in the U.S>.
Both bacteria and archaea can also protect themselves from viral infection with what system?
the CRISPR-Cas system
Every time the host divides, it copies the phage DNA and passes the copies to what?
the daughter cells
What does it mean for viruses to be obligate intracellular parasites?
they can replicate only within a host cell
Others have molecular components such as envelope proteins that are ________________.
toxic
Some viruses cause infected cells to produce ______________ that lead to disease symptoms
toxins
is a harmless derivative of pathogenic microbes that stimulate the immune system to mount defenses against the harmful pathogen
vaccine
Viral envelopes contain a combination of what two molecules?
viral and host cell molecules
Is usually derived from the host cell's plasma membrane as the viral capsids exit
viral envelope
Vaccines can prevent certain types of what illnesses?
viral illnesses
A phage that reproduces only by the lytic cycle is called a:
virulent phage
an infectious particle consisting of genes packaged in a protein coat
virus
Are viruses or prokaryotic cells more simple in structure?
viruses
Where is the broadest variety of RNA genomes found?
viruses that infect animals
Do bacteria have their own defenses against phages?
yes
