Chp 6: Acellular Pathogens

viroids (from class)

"silencing RNA"; interfere w/ normal translation of mRNA in *plants*---> mRNA gets made but does not get translated single stranded, naked *NO CAPSID* RNA RNA *does not* code for any proteins cause a number of plant diseases, resulting in crop loss *these are NOT viruses B/C they lack a capsid--> primarily infect plants* these do not cause illness in humans, only cosmetic in plants (Potatoes on the right are infected with viroids.)

what are the 3 shapes of viral capsid?

*1. helical*: cylindrical or rod shaped, with genome fitting just inside the length of the capsid i.e. *TMV*- naked helical virus, and *Ebola*- enveloped helical virus *2. polyhedral*: form poliovirus and rhinovius; consist of a nucleic acid surrounded by a polyhedral (many sided) capsid in the form of a icosahedron -----> *icosahedral* capsids are 3D, 20 sided structures with 12 vertices. (look like a soccer ball) -both helical and polyhedral viruses can have envelopes* *3. complex*: viral shapes seen in certain types of bacteriophages, such as T4 phage, and poxviruses, like vaccinia virus, may have features of both helical and polyhedral viruses so they are described as a *complex* viral shape; poxviruses are often brickshaped

describe a virus's method of replication: compare lytic and lysogenic cycles

*ALL* viruses use some version of *LYTIC cycles* *SOME* viruses *(IN ADDITION TO LYTIC CYCLE)* use *LYSONGENIC* cycle as means to replicate

what is the difference between generalized transduction and specialized transduction?

*generalized transduction* occurs during *lytic cycle* (random piece of DNA is transferred by the phage) *specialized transduction* occurs at the end of the *lysogenic cycle* (when the prophage is excised and the bacteriophage enters the lytic cycle)

Lysogeny

*the process in which a bacterium is infected by a temperate page.* Results in formation of *prophage*, where virus's DNA fuses with the host's DNA. *Lysogenic conversion* may result if the viral prophage carries genes for toxins or antibiotic resistance. *Induction* occurs when the prophage "pops out" of the host's DNA.

like viroids and virusoids Tobacco Mosaic Virus infects plants. How do these three types of plant pathogens differ from each other?

*viroids* have SS genome w/ naked RNA, and their RNA does not code for any proteins. results in crop loss due to unattractive crops. inability to code for proteins stops cells' translation. viroids infect plants only. *virusoids* also have a single stranded genome, and require a helper virus to replicate. while almost all virusoids only infect plants, there is an exception: Hepatitis D (with help of Hep B) *TMV* also has a SS genome, but is surrounded by a capsid. TMV can only infect the tobacco plant or related kins of plants

virulent phages vs. temperate phages

*virulent phages* typically lead to the death of the cell through cell lysis *temperate phages* can become part of a host chromosome and are replicated with the cell genome until such time as they are induced to make newly assembled viruses called *progeny viruses*. (it is typical of temperate phages to be latent or inactive within the cell.)

viral genomes may vary by 4 characteristics of their genetic information. what are they?

-type of nucleic acid (RNA or DNA) -# of strands of nucleic (ss single stranded or ds double stranded) -the sense/polarity of the strands (+ or -) -the structure (circular or linear)

Lytic cycle steps

1. Attachment: the phage attaches to the surface of the host; very critical in whether or not a viral infection will ever get started. 2. Penetration: the viral DNA enters the host cell; aka entry--> has to be viral genome, viral genome "enters" host cell 3. Biosynthesis/synthesis: phage DNA replicates and phage proteins are made; viral genome hijacks the host cell processes 4. Assembly/ Maturation: new phage particles are assembled; in infected cells's cytoplasm or ERs or Golgi--> viral parts get assembled 5. Lysis: the cell lyses, releasing the newly made phages; viruses escape host cell (could be through lysis/bursting of host cell or budding out of host cell, as in acquiring an *envelope*)

Lysogenic cycle steps

1. Attachment: the phage attaches to the surface of the host; very critical in whether or not a viral infection will ever get started. 2. Penetration: the viral DNA enters the host cell; aka entry--> has to be viral genome, viral genome "enters" host cell 3. Integration of Viral DNA into host cell's DNA 4. Viral DNA (now called prophage or provirus); can be transcribed & translated; cab cause frameshift insertion mutations if it inserts into exons 5. There may be a future return of the virus to *lytic cycle* of replication *(lytic cycles and lysogenic cycles usually drawn as figure 8)*

list 2 effects that a bacterium that has undergone Lysogenic conversion could have on human health.

1. Bacteria carrying proviruses can *acquire antibiotic-resistance genes or genes for making toxins* through transduction. (compromised immunity) 2. Viruses that form proviruses in human DNA may be *oncogenic (cancer-causing)*.--> death *Proviruses cannot be eliminated from human DNA.*

How HIV infects a cell

1. HIV fuses to the host-cell surface 2. HIV RNA, reverse transcriptase, integrase, and other viral proteins enter the host cell 3. Viral DNA is formed by reverse transcrition 4. Viral DNA is transported across the nucleus and integrates into the host DNA 5. New viral RNA is used as genomic RNA and to make vial proteins 6. New viral RNA and proteins move to the cell surface and a new, immature HIV forms 7. the virus matures when protease releases the proteins that form the mature HIV

put the steps of a viral lytic cycle in order from first to last

1. attachment 2. entry (penetration) 3. Synthesis (biosynthesis) 4. Assembly (maturation) 5. Release (lysis)

what are the 5 steps of the *Lytic Cycle*?

1. attachment 2. Entry/Penetration 3. Biosynthesis/Synthesis 4. Maturation/Assembly 5. Lysis/Release

what 3 things are embedded in the envelope of influenza?

1. hemagglutinin glycoprotein 2. neuraminidase glycoprotein 3. ion channel

what 4 hosts or types of hosts does influenza infect?

1. humans 2. pigs 3. other mammals 4. birds

what are 4 ways in which viruses can differ from each other:

1. structure 2. genomic makeup 3. host range 4. transmission mechanism (can also have a difference in vaccine availability)

5 steps of transduction

1. viral attachment and penetration: the phage insects a cell 2. integration: the phage DNA becomes incorporated into the host genome (*remember* this step will be different with viral infection amongst humans i.e. endocytosis) 3. Excision: The phage is excised from the bacterial chromosome along with a short piece of bacterial DNA. The DNA is then packaged unto newly formed capsids. 4. Infection: Phage containing both viral and bacterial DNA infect a new host cell 5. Recombination: The phage DNA, along with the attached bacterial DNA are incorporated into the new cell

when did the first recognized Ebola virus outbreak occur?

1976

Viral structures

A pathogen is a virus if it has a *genome* (DNA or RNA) surrounded by a protein coat called a *capsid*. Some of the viruses that infect humans and animals have *envelopes*, which are phospholipid bilayers surrounding the viral capsid. *Bacteriophages* need additional structures to get past the *peptidoglycan* cell walls of bacteria.

abnormally folded prion.

Abnormal prions exhibit an enzymatic action when they touch normal prions. (pictured is Prion PrP)

Transduction in Viruses:

Another way that bacterial genes transfer from a donor bacterium to a recipient bacterium. This process uses a *bacteriophage* *(REMEMBER: this is a virus)*

why are scientists and physicians concerned about Zika's spread?

B/C infection in pregnant women may lead to microcephaly and other neurological defects in their child. there is also no vaccine available.

HIV proviruses do not insert at random. Why would random insertion be counterproductive?

B/C it would cause a frameshift and then would not replicate within the host

why are adenoviruses important to researchers?

B/C they are like bacteriophages, and are also used as vectors in gene therapy

Why can't humans catch Tobacco Mosaic Virus?

B/C we are not a tobacco plant; we are not within that viruses host range

why are observable cytopathic effects an important diagnostic tool?

B/C you can observe them under a microscope when there is a lack of physical symptoms

Impact of lysogenic cycle on human health

Bacteria carrying *proviruses* can acquire antibiotic-resistance genes or genes for making toxins through *transduction*. Viruses that form proviruses in human DNA may be *oncogenic* (cancer-causing). *Proviruses cannot be eliminated from human DNA.*

These are *viruses that infect bacteria*. Bacteriophages are used in some eastern European countries to treat bacterial infections when *antibiotics are unavailable or do not work*. lots found in human resident microbiota

Bacteriophages

how does a bacteriophage acquire a host bacterium's DNA?

Bacteriophages acquire the bacterium's DNA during the assembly step of a Lytic Cycle

Cultivating viruses

Cannot grow them directly on Petri dishes. Need host organism or cell. Embryonated chicken eggs or cell cultures (yeast, bacterial, eukaryote) are used to cultivate viruses used to manufacture vaccines. (photo shows injection sites that are commonly used) Bacteriophages can be cultivated in bacteria on Petri dishes or in broths.

what doctors use. Ex: Human Immunodeficiency Virus or HIV.

Common name

Viral genome (genetic material)

DNA or RNA, some viruses have *both* of these nucleic acids in their capsids. (some dont DNA *at all* some have RNA i.e mRNA) Single-stranded or double-stranded Linear or circular Some viruses have 1 molecule of nucleic acid and others have multiple molecules. ---> different viruses will have different genomes The # of genes is small compared to the # found in cells.

Host range

Determined by types of hosts and cells a virus can infect. Virus must be able to locate a *particular surface receptor* molecule on an organism or cell in order to infect it. Ex: "Flu Attacks" animation from YouTube refers to *"locks" (host cell receptors) and "keys"* (molecules on the virus's surface) that must be complementary for infection to occur. i.e. a human cannot get Tobacco Mosaic Virus

Viruses that infect human cells

Entry and release steps are *different from viruses that infect bacteria*. (i.e. step 2 here is penetration of cell through endocytosis) Viral genome frequently enters our nuclei and "hijacks" our cells. *There is no transduction between humans!* (That would be incredibly strange.)

T or F? viruses typically have a wide host range

False. most viruses will only be able to infect the cells of one or a few species of organism viruses will typically only infect specific hosts and only specific cell types within those hosts

T ot F? autoclaving sterilizes prion contaminated instruments.

False. autoclaving does *NOT* sterilize prions. must incinerate also, pH does not seem to affect it

ends in "-viridae". Ex: Family Retroviridae

Family name

how to name a virus

Family name ends in "-viridae". Ex: Family Retroviridae Genus name ends in "-virus". Ex: Lentivirus Common name is what doctors use. Ex: Human Immunodeficiency Virus or HIV. There may be subspecies designations. Ex: HIV-1 or HIV-2.

What occurs when two or more influenza viruses infect a single host?

Genome segments can reassort to produce a new combination of segments, and give rise to a new virus strain

ends in "-virus". Ex: Lentivirus

Genus name

HIV: a retrovirus

HIV is a single-stranded RNA virus that carries *reverse transcriptase* and *integrase enzymes* in its capsid. These enzymes allow it to form a provirus in human DNA, where its genome is safe from our immune system and from drugs. (remember: we can not grow viruses in a lab b/c viruses need a specific host cell to replicate)

Give an example of Retroviridae

HIV-1

Give an example of a virus that has both RNA and DNA.

Hep B

Viral Classification

ICTV or Baltimore classifications rely on genome type and method of replication. ICTV classification also uses the viral shape. *There is no binomial nomenclature for viruses.*

Characteristics of Viruses

Infectious, acellular pathogens Obligate intracellular parasites w/ host and cell type specificity DNA or RNA genome *Genome surrounded by protein capsid Some viruses have phospholipid envelopes covered w/ viral glycoproteins Cannot reproduce without using host cell's structures (mostly through *lytic cycle* but for some viruses also *lysogenic cycle*)

more on viral structure

Influenza virus causes what Dr's consider flu———> "stomach flu" *(gastrointeritis)* can have multiple viral or bacterial causes *"pink" copy machine* = RNA viral genome ex: "yellow noodles" —-> influenza viruses have single-strands of RNA genome *"blue explosion"* influenza virus's capsid. *influenza virus is an example of an envelope virus. so is HIV.* Majority of viruses do not have envelopes around their capsid. But many animal-and-human-infecting viruses do. "knobs or spikes" on influenza envelope- used to attach virus to host cell's receptors. bird flu has knobs or spikes that have mutated and can infect our cells

when did zika virus first appear in the United States?

January 2016

Viruses that replicate using the __________ cycle cause lifelong infections.

Lysogenic

Characteristics of Viruses Cont'd

Majority are too small to be seen without electron microscopes. Majority of known viruses do not infect human cells. Viruses and bacteria are different! We've seen that bacteria are prokaryotic cells. Viruses are not even cells. (Forget what you hear on the news. They never get it correct.)

what is the only known human virusoid, and what makes it special?

Only known human virusoid is Hepatitis D, which must be transmitted with Hepatitis B virus in order to replicate. (Hep B vaccine protects you from both!)

Virusoids (aka "satellite viruses")

Single-stranded RNA (non-self-replicating) *Almost* all are *plant pathogens*. (like viroids these can infect commercially important agricultural crops) Require a helper virus to infect the same host cell before they can replicate. *Only known human virusoid is Hepatitis D, which must be transmitted with Hepatitis B virus in order to replicate. (Hep B vaccine protects you from both!)*---> currently only 5 described types of virusoids and their associated helper virus (helper viruses are all from the family *sobemoviruses*)

Enveloped viruses

Some viruses that infect humans and animals have an additional layer called an *envelope* made of a small portion of a phospholipid membrane *Viruses do not make their envelopes, but steal plasma membrane from host cells they infect.* Viral envelopes do not actively transport materials in & out, so they are no longer plasma membranes.

Give an example of a bacteriophage used to treat a virus that is not harmful to its human host

T4 bacteriophage only infects *E. coli bacteria, not humans*.

how does the # of genes in a viral genome compare to the # of genes found in cells?

The # of genes is small compared to the # found in cells. *viral genome is about the size of single plasmid (much smaller than E. coli)*

Cytopathic effects

These are physical changes seen in virally-infected cells observed with microscope. Can be diagnostic. i.e. pap smear is swabbing of cervical cells Ex: rabies, human papillomavirus *REMEMBER: these are NOT symptoms in patients, but what's happening in the cell*---> not the fever or the rash, but what's actually happening in the cell Can include: abnormal #'s of nuclei, giant fused cells, abnormal plasma membrane, unassembled viral parts inside host cell Ex: the next 3 slides show measles virus infecting monkey kidney cells (shown are monkey kidney cells)

Prions

They are *NOT* viruses. Recent research confirms this. instead they are *proteinaceous infectious particles* (b/c proteins are acellular and do not contain DNA or RNA) replication by enzymatic conversion They are *infectious proteins* that cause *rare brain diseases*, such as Creutzfeldt-Jakob Disease (CJD). i.e. mad cow disease (likelihood of acquiring an infection from contaminated meat is actually very low) Most human cases have genetic causes and even these are rare. Eating contaminated meat is another documented cause. (also even more rare is result of transplant) *prions are MOST resistant pathogens known*

Where do proteins used to make viral capsids come from?

They are synthesized by the host cell's ribosomes

Transduction

This process requires a donor bacterium, a recipient bacterium, and a virus capable of infecting both. The donor bacterium is infected and killed by the virus as it replicates. Some of the new viruses contain donor bacterium DNA instead of viral DNA. These are transducing viruses. The recipient bacterium then gets infected with transducing viruses.

which virus was the first identified and described?

Tobacco Mosaic Virus (TMV)

T or F? viruses can NOT make their own structures.

True

T or F? viruses don't code for much beyond their capsid protein and special enzyme

True. viruses rely heavily on host cell to get replicated. special enzyme is specific to survival of that virus. i.e. HIV specific enzyme

Normal prion

We have normal prions in our brains. (pictured is a cellualr PrP)

lysogen

a bacterial host with a prophage

what is the protein coating surrounding a virus's genome called?

a capsid

Viroids (from book)

a cellular particle meaning "virus-like" consists only of a short strand or circular RNA capable of self-replication 1st one to be discovered was found to cause potato tuber spindle disease, which causes slower sprouting and various deformities in potato plants results in devastating crop losses of commercially important agricultural food crops grown in fields and orchards

how long can a virus remain in a host once the provirus has been established?

a long time

what is a prion? (think structure)

a prion is a misfolded rogue form of a normal protein (PrPc) found in the cell. this rogue prion protein (PrPsc), which may be caused by a genetic mutation or occur spontaneously, can be infectious, stimulating other endogenous normal proteins to become misfolded, forming plaques.

How does Virus Explorer define vaccines?

a substance that, when taken into the body, should induce a protective immune response to a virus. an individual who has been vaccinated against a virus should be prepared to fight that infection

zoonotic

a virus that is transmitted from a vertebrate animal (for example rodent or bat) to humans

what five types of hosts do adenoviruses infect?

a. human & other mammals b. birds c. reptiles d. fish e. amphibians

Which of the viruses with human hosts in virus explorer *DO NOT* have envelopes?

adenovirus, and papillomavirus

lysogenic conversion (aka phage conversion)

alteration of host characteristics or phenotypes due to the presence of phage; the presence of the phage may alter the phenotype of the bacterium, since it can bring in extra genes (i.e. toxic genes that can increase bacterial virulence)---> results in a change in the host phenotype i.e. some bacteria such as Vibrio cholerae and Clostridium botulinum are less virulent in the absence of the prophage during lysogeny, the prophage will persist in the host chromosome until *induction* which results in the excision of the viral genomes from the host chromosome. after induction has occurred the temperate phage can proceed through a lytic cycle and then undergo lysongeny in a newly infected cell

vector

an animal that transmits a pathogen from one host to another--> mechanism of viral transmission i.e. arthropods such as mosquitoes, ticks, and flies mechanical and biological vectors

vector:

an organism that serves to transmit a virus from one host to another host

how are animal viruses different from bacteria viruses?

animal viruses do not always express their genes using the normal flow of genetic information: from DNA-->RNA-->to protein some viruses have a dsDNA genome like cellular organisms and can follow the normal flow. However, others may have ssDNA, dsRNA, or ssRNA genomes. the nature of the genome determines how the genome is replicated and expressed as viral proteins. if a genome is ssDNA, host enzymes will be used to synthesize a second strand that is complementary to the genome strand, thus producing dsDNA. the dsDNA can now can now be replicated, transcribed, and translated similar to host DNA.

How do enveloped viruses get an envelope?

as new viruses leave a host cell, they take a piece of plasma membrane with them

Which 2 replication steps do the Lysogenic Cycle and Lytic Cycle have in common?

attachment and entry

fx of "knobs or spikes" on influenza envelope

attachment of virus to host cell's receptors

what is the Fx of the knobs and spikes on a viral envelope?

attachment. used to attach virus to host cell's receptors.

from the virus' perspective, why is the host important?

b/c a virus can only replicate *INSIDE* of a host

why are envelopes not considered plasma membranes?

b/c they no longer actively transport materials in and out

biological vector

biological transmission occurs when the arthropod carries the viral pathogen *inside* its body and transmits it to the new host through *biting*

give an example of a virus whose knobs or spikes have mutated and what was the cause?

bird flu which mutated to be able to infect human cells

How is zika transmitted?

by mosquitoes of the genus Aedes

How do viruses make their envelopes?

by stealing a piece of the plasma membrane as they exit their host cell

which of the following is NOT a part of HIV? a. an envelope b. a capsid c. double-stranded RNA d. spikes for attachment

c. double-stranded RNA

How are TSEs transmitted?

can be transmitted between animals and from animals to humans by eating contaminated meat or animal feed (*very rare*); transmission between humans can occur through hereditary (as is often that case with GSS and CJD) or by contact with contaminated tissue, as might occur during a blood transfusion or organ transplant. there is no evidence for transmission via casual contact with an infected person.

what types of infections do adenoviruses cause in humans?

common but relatively mild clinical conditions such as: pink eye, the common cold, and bronchitis

which countries experienced widespread outbreaks in 2014?

countries in west africa, primarily across Sierra Leone, Guinea, and Liberia

describe a virus in your own words

distinct biological entity with no taxonomic labeling because they are *ACELLULAR*- meaning they are not made up of cells. their origin is still a speculation, and in order *to survive* and reproduce they must infect a *host cell* making them obligate intracellular parasites. the *genome* of a virus enters a host cell and directs the production of the viral components, proteins, and nucleic acids needed to form new virus particles called *VIRIONS*. New virions are made in the host cell by assembly of viral components. The new virions transport the viral genome to another host cell to carry out another round of infection

what domains to viruses infect?

domains: Eukarya Bacteria Archaea

reverse transcriptase

enzyme found in retroviruses that can make a copy of ssDNA from ssRNA

synyctia

exmaple of a cytopathic effect giant fused cells that result from infections w/ viruses like measles virus i.e. RSV- name comes from syncydium (respiratory)

T or F? Most viruses are lytic.

false. Most viruses are *LYSOGENIC*

T or F? Prions contain RNA

false. they contain infectious proteins only

prophage

forms when a virus's DNA fuses with the host's DNA during the lysogenic cycle

What is embedded in the envelope of HIV?

glycoprotein

This is SARS (Severe Acquired Respiratory Syndrome) virus, has an envelope. so what will it have on its surface?

glycoprotein spikes

put the viral classifications in order from least to most specific

group name family name genus common name subspecies #

what to "locks" refer to?

host cell receptors

How do you know if a pathogen is a virus?

if it has a genome surrounded by a protein coat called a capsid

what happens to the host cell in the lytic and lysogenic cycles?

in the lytic cycle of *virulent phage*, the bacteriophage takes over the cell, reproduces new phages, and destroys the cell in the lysogenic cycle, the phage genome also enters the cell through attachment and penetration (like the lytic cycle), but instead of killing the host, the phage genome integrates into the bacterial chromosome and becomes part of the host. the integrated phage genome is called a *prophage*.

Give 2 examples of envelope viruses

influenza and HIV

give an example of an envelope virus.

influenza virus

what determines the shape of of the capsid, or core?

it is determined by the arrangement of many individual proteins and is typically symmetrical (overall shape of protein layer that surrounds the virus genetic material)

In the name Picornaviridae, what does the -viridae suffix refer to?

it is the family name

Where did HIV come from?

it is thought to have evolved from the simian immunodeficiency virus (SIV); HIV is a distinct virus that infects humans

what does it mean for a virus to have a segmented genome?

it means that its genome is made up of multiple nucleic acid segments. this provides the mechanism for the evolution of new types of viruses

what are some examples of TSEs in humans?

kuru fatal familial insomnia Gerstmann-Straussler-Scheinker disease Creutsfeldt-Jakob disease

When a bacterium gains antibiotic resistance genes or genes for making toxins from a prophage, that bacterium has experienced ___________ _______________.

lysogenic conversion

life cycle of viruses with animal hosts

lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and releases *differences*--> mechanism of penetration, nucleic-acid biosynthesis, and release differ between bacterial and animal viruses enter through *endocytosis* or through membrane fusion (viral envelope with the host cell membrane) after binding to host receptors

what are the 2 methods of viral replication?

lytic replication and lysogenic replication see "Flu Attacks" or a similar animation from YouTube.

what are some examples of TSEs in animals?

mad cow disease scrapie (in sheep and goats) chronic wasting disease (in elk and deer)

describe the structure of a capsid

made of protein; interior is not filled with cytosol- as in a cell- but instead it contains the bare necessities in terms of genome and enzymes needed to direct the synthesis of new *virions*. each capsid is composed of protein subunits called *capsomeres* made of one or more different types of capsomere proteins that interlock to form the closely packed capsid

Lysogenic conversion

may result if the viral prophage carries genes for toxins or antibiotic resistance.

mechanical vector

mechanical transmission occurs when the arthropod carries a viral pathogen on the *outside* of the body and transmits it to a new host by *physical contact*

what to "keys" refer to?

molecules on the the virus's surface

what are the 2 categories of viruses?

naked viruses or nonenveloped viruses and enveloped viruses

virion

newly formed particle virus

is HIV considered a zoonotic virus?

no; it is considered human-to-human

Do all viruses have envelopes around their capsids?

no; majority do not have envelopes around their capsid

do the vaccines against papillomavirus protect against all known strains of HPV?

no; primarily protects against several sexually transmitted strains. in 2006 vaccines became available against strains that can cause genital warts and cancer

Induction

occurs when the prophage "pops out" of the host's DNA.

How do bacteria get infected with prophages?

only bacteriophages capable of performing both lytic and lysogenic cycles will cause prophages in bacteria

bacteriorphages are also known simply as what?

phages

retrovirus

positive ssRNA virus that produces and uses reverse transcriptase to make an ssDNA copy of the retroviral genome that can then be made into dsDNA and integrate into the host cell chromosome to form a provirus within the host chromosome i.e. HIV

PSTV

potato spindle tuber viroid--> typically spread when infected knives are used to cut healthy potatoes, which are then planted. like viruses- PSTVs take control of the host machinery to replicate their RNA genome.

what are the most resistant pathogens known?

prions

Viral DNA is also known as what?

prophage or provirus

lytic replication

results in death of host cell; don't stay in body very long-> in most cases a patient's immune system will defeat i.e. common cold virus

Lysogenic replication

results in incorporation of viral DNA into the host cell's DNA.

describe the arrangement of a viral genome

single stranded (ss) or double stranded (DS) they can be linear or circular usually symmetrical Some viruses have 1 molecule of nucleic acid and others have multiple molecules.

not all viruses have an envelope. if a virus has this outer layer, explain how it forms

some viruses exit their host cell by *budding* from its surface. in the process, part of the host cell membrane envelopes the virus particle forming an outer layer (made of viral proteins) called the envelope

tissue tropism

specificity of viruses; many viruses are host specific, meaning they only infect a certain type of host and most viruses only infect certain types of cells within tissues i.e. poliovirus--> exhibits tropism for the tissues of the brain and spinal cord influenze virus--> has a primary tropism for the respiratory tract

Describe what is inside of a retroviruses capsid (i.e. HIV-1)

ssRNA, reverse transcriptase, intergrase, protease *enveloped with spikes*

Ex: HIV-1 or HIV-2.

subspecies

measles causes monkey cells to become GIANT FUSED cells called what?

synyctia

what is the fx of prions?

the fx is not exactly known, but it is known that they are important in *synaptic reflexes*

HIV can direct the synthesis step of a lytic cycle while remaining in a provirus form. How does this occur?

the host cell's RNA polymerase transcribes the HIV provirus and the host cell's ribosomes translate the resulting mRNA into HIV proteins.

what determines a virus's host range?

the presence of complementary receptors on cells

the main difference in step 2 of transduction between how a virus infects a bacteria cell vs. how a virus infects an animal/human cell is:

the virus enters the host bacteria cell through *integration: the phage DNA becomes incorporated into the host genome* (virus initiated); while the host animal/human cell engulfs the virus through *endocytosis* (host initiated)

give an example of a satellite RNA that infects humans

the virusoid hepatitis delta virus (HDV) aka hepatitis delta virusoid HDV is much larger than a plant virusoid; has a circular ssRNA genome that can direct the biosynthesis of HDV-associated proteins the HDV helper virus is the hep B virus (HBV). *coinfection with HBV and HDV results in more severe pathological changes in the liver during infection, which is how HDV was first discovered*

describe what happens once a helper virus enters the host cell

the virusoids are released and can be found free in plant cell cytoplasm, where they posses ribozyme activity. the helper virus undergoes typical viral replication independent of the activity of the virusoid. ---> virusoid genomes are small. a virusoid genome does not code for any proteins, but instead serves only to replicate virusoid RNA

Lytic and Lysogenic cycles have what in common?

their first 2 steps ---> Attachment and Entry/Penetration

What are envelopes made of and what do they surround?

they are made of phospholipid bilayers that surround the capsid

what if the fx of integrase?

this enzyme cuts a human cell's DNA to allow HIV to form a provirus

What is the fx of protease?

this enzyme cuts the proteins in the interior of HIVs capsid to the proper length, resulting in mature HIV

what is the fx of reverse transcriptase?

this enzyme reads HIV template single-stranded RNA and converts it to HIV double-stranded DNA in a two-step process

What is a prophage (provirus)?

this term refers to viral DNA that has inserted into host cell DNA

Why do bateriophages need additional structures?

to get past the peptidoglycan cell walls of bacteria

what type of horizontal gene transfer are the lytic and lysogenic cycles?

transduction

Spongiform encephalopathy due to CJD, a prion disease.

transmissible spongiform encephalopathy (TSE): caused by prions---> found in humans and animals rare degenerative disorder that affects the brain and nervous system; the accumulation of rogue proteins causes the brain tissue to become sponge-like, killing brain cells and forming holes in the tissue, leading to brain damage, loss of motor coordination, and dementia. infected individuals are mentally impaired and become unable to move or speak. *there is no cure, and the disease progresses rapidly, eventually to death within a few months or years*

T or F? some viruses can have both DNA and RNA in their capsids

true i.e. Hep B

T or F? spikes are found on naked and enveloped viruses

true.

T or F? you are more likely to see cytopathic effects in a lytic cycle.

true. you may never see the virus at all during a lysogenic cycle (visible in bacterial lawn w/ E. coli---> view viral plaques under microscope; could see where the E. coli has lysed)

What would you need to do before using PCR to help classify a virus?

use an enzyme to turn RNA to DNA, THEN you can do PCR

review: what is the difference between vertical and horizontal gene transfer?

vertical gene transfer: genetic info passed from parents to offspring our parental generation to daughter cell Three types of horizontal gene transfer occur in bacteria: Transformation Conjugation *Transduction* (*These do not occur in humans.*)

what is the main difference between virus and viroids?

viroids do not have a protein coat to protect their genetic information

how are plant virusoids different from satellite RNAs?

virusoids belong to a larger group of infectious agents called *satellite RNAs*, which are similar pathogenic RNAs found in *animals*. unlike the plant virusoids, satellite RNAs may encode for proteins; however, like plant virusoids, satellite RNAs must coinfect with a helper virus to replicate.