BIOL 206 Exam 2
Obligate intracellular parasites/ pathogens
Viruses ; are not capable of reproducing or metabolizing outside of a living host
Outside of cells, viruses exist as ___
Inert macromolecules
T/F: viruses are acellular
T
The viral genome can be made of ____
DNA or RNA
the types of viral genomes are
dsDNA, ssDNA, dsRNA, ssRNA
Range in size of viruses
10 nm to 500 nm
What surrounds the viral genome?
A protein capsid; some viruses have an envelope surrounding the capsid
How do viruses replicate?
By using the machinery of the host cell
What is the range in size of living cells?
200 nm to 12 cm
Viruses do not have ribosomes. What does this mean?
Ribosomes are the site of translation. Therefore, viruses cannot independently make protein products
What viral family includes chicken pox and cold sores?
herpes
What type of microscope is needed to visualize viruses?
electron microscope
____ viruses have capsids
all
What is a capsid?
protein coat surrounding a virus and protecting its genome
A capsid is made of identical protein subunits. What are these subunits called?
Capsomeres
What is the composite structure of the capsid and nucleic acid?
Nucleocapsid
What are the four viral shapes?
Filamentous/ helical, icosahedral, enveloped, complex
Filamentous/ helical viruses
flexible, curved, or coiled. Tubular, continuous helix of capsomeres. Examples include ebola and tubulovirus
Icosahedral
Any type of polyhedral shape. Has peplomeres, or spike proteins. One example is adenovirus.
These vary in the numbers of capsomeres, but each capsomere is made up of variable amounts of proteins.
Enveloped virus
Can be a virus of any shape; must have spike proteins; buds out of a cell and envelopes itself in host cell membrane. Includes covid, herpes, and rabies
The envelope is ____ the nucleocapsid
outside
What is the function of an envelope?
An envelope helps a virus to evade the host immune system. This also allows for easy fusion with other cells
T/F: an enveloped virus is infective without the envelope
F
Complex virus
A virus with a complicated structure, such as a bacteriophage. Usually has a head, tail, and tail fibers
What is the shape of the rabies nucleocapsid?
Bullet shaped
Viruses are typically species specific. Why is this the case?
Specific proteins are produced by the virus to attach to the complementary host cell receptors
Conserved receptors
Protein receptors that are the same among different species. This allows for viral transmission between some species.
Bacteriophages cannot have an envelope. Why?
Bacteria have cell walls, which preclude phages from budding out and wrapping themselves in membrane.
Peplomeres are essential for ___ and ___
infectivity and attachment
A virus that does not have an envelope is called a ____ virus
naked
Function of the viral envelope
Protection of the nucleic acid, binding and infectivity, helps evade immune response
Molecular mimicry
close resemblance between foreign and self-antigen; enveloped viruses "disguise" as a host cell
How does a naked virus attach to the host cell?
The peplomeres of the capsid attach to the cell receptors
T/F: Enveloped viruses are infective without an envelope
False
Are naked or enveloped viruses harder to kill on surfaces?
Naked; the envelope of the latter is easily damaged by temperature, pH, pressure, toxins, and detergents.
Are naked or enveloped viruses harder to kill in the body?
Enveloped; the envelope helps it to evade the immune system
Virion
Single virus
T/F: Anything that damages cell membranes damages viral envelopes
T
When growing viruses in a laboratory setting, that media must be used?
Living cells
How may animal viruses be grown?
In living animals, embryonate eggs, or cell cultures
Growing viruses in living cells carries a small risk of _____
Product contamination from the growth medium
When lawns of bacteria are exposed to phages, they form ____
plaques
In order for infection, viruses must ____
interact with host cells
Viruses are ____motile
non
Chemical attraction of viruses allows them to _____
sense host cells
There are three mechanisms by which animal viruses can enter host cells. What are they?
Direct penetration, membrane fusion, endocytosis
Direct penetration
The nucleic acid of the virus enters the host cell. This is only done by naked viruses
Membrane fusion
Enveloped virus melts into the cytoplasmic membrane of the host cell, allowing entry of the nucleocapsid
Endocytosis
The entire (naked or enveloped) virus is taken into the cell. This action is triggered by a peplomere that binds to a receptor that triggers endocytosis
Upon entry to the animal cell, viruses with a capsid are required to ____
uncoat
Budding / blebbing
Exocytosis of enveloped virus; nucleocapsid binds to the membrane internally, which then pinches off.
Lysis
Process by which a cell bursts, releasing naked viruses
Lysis from poxvirus releases ___ virions
3k - 4k
Lysis from poliovirus releases _____ virions
over 100k
Describe the process of budding / blebbing
The spike proteins embed in the host cell membrane at the site of budding. The nucleocapsid then bind the intracellular side of the membrane and begins to exit. The membrane is wrapped around the virion, and eventually it pinches off
T/F: Enveloped viruses kill the cells
T
Only the ____ of phages can enter the bacteria
nucleic acid
Phage always exit a cell by ___
lysis
Viral host range
Refers to the number of species that a virus can infect. This depends on the presence of peplomeres and their complementary receptors in the tissues
Rabies has a ____ host range
broad
The T4 bacteriophage has a ____ host range
narrow
The t4 phage infects
E Coli
List the five steps of phage replication
Adsorption/attachment, penetration, biosynthesis, maturation, release
Describe the adsorption/attachment phase of the phage life cycle
Binding of virus to receptors
Describe the penetration stage of the phage life cycle
Genome enters the cell
Describe the biosynthesis stage of the phage life cycle
Production of viral components
Describe the maturation phase of the phage life cycle
Assembly and completion of the viral formation; this occurs spontaneously
Describe the release phase of the phage life cycle
Release by lysis
Burst time
time from attachment to lysis
Burst size
number of viral particles released
Burst size of E coli
about 200 virions
Enveloped viruses differ in two steps of the replication process from phages and naked viruses. What are they, and why?
Enveloped viruses fuse into the cell (penetration), and bud out (release)
E. coli bacterial morphology
Gram - bacillus
The T4 phage releases ___ to weaken the cell wall of e coli
lysozyme
the LPS of gram - bacteria can act as ____ for phages
binding sites
Lysogenic cycle of phages
Occurs under favorable conditions. Viral genome inserts into the host genome and replicates along with the host cell
Lytic cycle of phages
Occurs under poor conditions. The virus replicates into new virions and lyses the cell
T/F: phages can switch from the lysogenic to lytic cycle
T
Stages of phage maturation
In order of formation: base, tail, sheath, DNA, capsid, mature head, tail fibers
What viruses are capable of crossing into the human genome?
DNA viruses or retroviruses
HPV
DNA virus; causes cervical, throat, and anal cancer
Hepatitis
DNA virus, can cause liver cancer
DNA or retroviruses do not always cause cancer. When do they?
When they cross over into oncogenes or DNA repair viruses
Retroviruses
use reverse transcriptase (aka RNA dependent DNA polymerase) to copy their RNA genome into DNA
MMR vaccine stands for ________
Measles, mumps, rubella
Ro
R naught; refers to the number of people an infected person infects
Ro < 1
Does not pose a risk for major infectivity
Ro > 1
Poses a risk for viral spread
Measles
Can be fatal or cause brain damage. Highly contagious (Ro = 13 - 18) Typically deadly to small children
Effect of mumps
Can cause sterilization of boys; scars the epididymis
Rubella/ German measles
Less contagious than measles. Causes miscarriage or birth malformations
What percent of a population must be vaccinated for herd immunity to take effect?
95%
What is another name for lysogenic phages?
Temperate phages
Temperate phages undergo what two stages of the lytic cycle?
Adsorption, penetration
Prophage
A phage genome that has been inserted into a specific site on the bacterial chromosome.
Integrase
the enzyme responsible for integrating viral DNA into the host cell's DNA
In order to cross over into the host genome, lysogenic viruses need a _______
complementary DNA sequence
Induction
process by which a prophage is activated and enters the lytic cycle
Causes of induction
UV light, chemicals, environmental cues
Lysogenic cycle
Phage attaches and injects DNA, phage DNA circularizes, phage DNA enters the bacterial chromosome, bacteria reproduces, prophage may exit the genome in an induction event
Lytic cycle
Phage attaches and inserts DNA, phage DNA circularizes, new phage DNA and protein are synthesized and virions assemble, cells lyse
Method of transduction
transduction is the process by which phages transfer DNA between bacteria. This occurs when the viral DNA, upon exiting the host genome, takes a few complementary base sequences along with it
Biosynthesis of DNA viruses
DNA replication, transcription, translation
How do DNA viruses replicate their DNA?
by using host DNA polymerase
how do DNA viruses transcribe their genomic sequences into RNA?
By using the host RNA polymerase
How do DNA viruses perform translation?
By using the host ribosome
+ ssRNA viruses
Viral RNA serves as mRNA for protein synthesis
- ssRNA viruses
Viruses whose must carry an RNA-dependent RNA transcriptase for transcribing mRNA from the -RNA genome so that protein can then be translated.
Is COVID enveloped?
yes
The genome of covid is ____
+ ss RNA
RNA is more unstable than DNA. This means that RNA viruses are more likely to ____
mutate
4 main structural proteins of viruses
spike (S), envelope (E), membrane (M) glycoproteins, and nucleocapsid (N) proteins
In addition to the 4 main structural proteins of viruses, the COVID genome codes for ____ nonstructural proteins that aid in ______
16; aid in viral replication, maturation, and release
The covid vaccine provides immunity to the ____ glycoprotein
S
Portals of entry to host (covid)
nasal and oral passages and conjuctiva of eyes
The S proteins of covid bind to the ____
angiotensin - converting enzyme 2 (ACE2), a conserved structure
Binding to the ACE2 receptor triggers
Endocytosis and membrane fusion
the AEC2 protein is present in what tissues?
lungs, kidneys, heart, arteries, GI tract
Functions of the ACE2 protein
Lowers blood pressure, regulation of fluid balance, regulation of the inflammatory response
Stages of covid manifestation
Asymptomatic stage, upper airway response, hypoxia
Stage 3 covid / severe disease manifestation
Hypoxia, progression to acute respiratory distress syndrome (ARDS). Requires critical care, and 15% of covid patients require oxygen. Lungs fill with fluid, white blood cells, mucus, and cellular debris. Characterized by cytokine storms, extreme fatigue, cyanosis, confusion
Cytokine storms
Overproduction of cytokines which can cause significant damage by attacking the body's tissues. Leads to dramatic drops in blood pressure, leaky blood vessels, formation of blood clots, and organ failure
Cytokines
Hormone-like chemicals facilitating communication between brain and immune system.
How do mRNA vaccines work?
mRNA coding for the S proteins + lipid is incorporated into the vaccine. This mRNA stimulates the body to make an antibody to the spike protein
What are the most common routes of getting antibodies?
Getting the disease, a traditional vaccine, or an mRNA vaccine
Steps of synthesizing a traditional vaccine
Grow healthy cells and infect with them with the virus.. The virus can then be grown and harvested. This product is then purified and killed
In a traditional vaccine, the _____ virus enters the host cell
entire
Vaccines are tested for _____
safety, efficacy, and safety in large populations
Synthesis of mRNA vaccine
Synthesize the sequence and incorporate it with lipid to facilitate entry into the cell
Viriophage
virus that attacks viruses
Mamavirus
virus that is infected by the Sputnik virophage; largest viral genome; largest capsid; found in amoebas
Prions
Proteinaceous infectious particles. Slow, persistent, and deadly. Transmissible spongiform encephalopathies .
How are prions acquired?
They can be ingested, inherited, or introduced by surgical instruments
Types of prion diseases
Sheep scrapes, Creutzfeldt-Jakob disease, kuru, fatal familial insomnia, mad cow disease
PrPc
Normal cellular prion protein, found in brain and CNS. Functions in regular cell death and differentiation
PrPsc
Scrapie protein; accumulates in brain and forms plaques or fibrils. This serves as a template to cause the misfolding of other proteins
Prions are ____ to enzymes
resistant
Kuru
TSE in humans that is caused by cannibalism; progressive, fatal; affects the CNS and causes derangement and loss of motor function. Often found in cannibalistic tribes in New Guinea
Creutzfeldt-Jakob disease
Rare form of human TSE; genetic; usually affects those over the age of 50. This often presents after a founder event/ genetic bottleneck
vCJD
Variant Creutzfeldt-Jakob disease; aqcuired from corneal transplants, the use of growth hormones from cadavers, improperly handled surgical instruments, and injection of prion contaminated meats
BSE/ mad cow
Caused by using bone meal and sheep tissue as a feed additive in cattle. This was also linked to an elimination of treatment of feeds with organic solvents
What steps were taken by the US to prevent TSE?
1989 ban on beef imports from Britain, 1997 ban of sheep/beef use in some animal feeds
Prions are resistant to ___
Formaldehyde, ethanol, proteases, radiation, high heat
Prions are sensitive to ___
Bleach, phenol, strong detergents, autoclaving (heat + pressure), organic solvents
in order for prions to be transmitted via ingestion, what kind of tissue must be ingested?
neural tissue
Viroids
Plant virus; circular ssRNA
Viroids enter a plant through ____
wounds or via insects
Examples of viroids
potato spindle tuber disease, avocado sunbloch
Size of viroids
1/10th size of RNA viruses
Size of viruses (largest to smallest)
Viruses, virophages, prions, viroids