Microbiology: Bacteria and Viruses Flashcards
Describe the lytic cycles of bacteriophages
A lytic life cycle always end up destroying it the host cell that the virus infected: the virus produces the early gene of hydrolase, which degrades the entire host’s genome. The dNTP’s from this genome are then used to create multiple copies of the phage genome. New proteins are also synthesized for the capsid for each new genome. After that, the virus will express the late gene of lysozyme, which degrades the bacteria’s cell wall, causing it to lyse and release ~100 viral progeny
Describe the lysogenic cycle of bacteriophages
When the virus injects its genome into the host cell, it incorporates this genome into the host cell’s genome. This virus is now considered a prophage, and the host is now referred to as a lysogen. The prophage is silent thanks to its repressor proteins that bind to specific DNA elements in the phage promoters (operators). Therefore, the viral genes are not expressed and viral progeny are not produced; however, when the host reproduces itself, the prophage is also reproduced. The prophage has the ability to remove itself from the genome (process called excision) and become activated, which means it’ll undergo the lytic cycle; however, excision and followed by the lytic cycle will only occur if the host cell itself experiences stress (i.e. high temps, change in pH, or change in salt concentration of surrounding solution)
The first step of viral infection is the binding to the exterior wall of the bacteria in a process called ______
attachment or adsorption
After the virus has undergone attachment/adsorption, it injects its genome into the host cell in a process called _____
penetration or eclipse (called eclipse because the capsid remains on the outer surface of the bacterium while the genome disappears into the cell, removing the infectious virus from the media)
What is transduction?
Refers to transfer of host cell DNA to another host via a bacteriphage. This occurs when the lysogenic virus undergoes excision, and will excise some host cell genome in addition to its own genome.
What is an envelope on a virus? How does the virus obtain this?
Refers to an outer covering on the capsid, which is obtained by budding though the host cell’s membrane. Thus, this envelope is comprised of phospholipids, proteins, and carbohydrates from the host membrane.
To infect a new host, some enveloped viruses fuse their envelope with the host’s plasma membrane, which leaves the de-enveloped capsid inside the host cell.
What is a naked virus?
refers to a virus that doesn’t contain an envelope.
all viruses that infect bacteria and plants are naked viruses.
*Side note: all envelope viruses are animal viruses, but not all animal viruses must contain an envelope to infect animal cells.
All phages and plant viruses are naked. Why?
phages and plant viruses infect hosts that possess cell walls; therefore budding is not possible. When the virus exits the cell, the cell wall is destroyed and the host membranes rupture, so there is no membrane left in which to bud with.
Describe the productive life cycle
- Like the lytic cycle, but without lysis. Viral copies leave via the process of budding, which results in an enveloped virus.
- This life cycle is only found in viruses that infect animal cells
Only _____ cell viruses undergo the productive cycle
animal
What are the advantages of an envelop on a virus
It allows the virus to be less detectable to the immune system (although the immune system will eventually recognize the enveloped virus)
It allows for easier infection because the enveloped virus will be able to attach to a cell specific receptor on the host cell. The cell will swallow the enveloped virus as a whole, allowing the whole virus genome to enter the host cell and allows the capsid to be recycled.
Briefly describe the process of how positive sense RNA replicates via a lytic cycle
positive sense RNA can be picked up by host ribosomes and directly be translated. Hydrolase and viral proteins will first be translated and synthesized. The translated positive sense RNA will be translated and synthesized into a new strand of negative sense RNA (complementary to the positive sense RNA). RNA dependent RNA polymerase will use that negative sense RNA strand to synthesize multiple new positive sense RNA strands. Each strand will become a new viral genome.
Briefly describe the process of how negative sense RNA replicates via a lytic cycle
once -RNA is injected into host cell, the RNA dependent RNA polymerase must first create a positive sense strand of RNA. That +RNA can then be translated by a ribosome, which will be translated into a -RNA.
Is RNA dependent RNA polymerase carried by the virus, or is the code incorporated into the viral genome
+ RNA viruses: incorporated into the viral genome only
- RNA: actual enzyme is carried with the virus in addition to also must carry the code in the genome
What enzyme is responsible for converting viral RNA into ssDNA?
RNA dependent DNA Polymerase (aka reverse transcriptase)
What is a retrovirus?
refers to the +RNA virus that contains an encoding for reverse transcriptase (aka RNA dependent DNA Polymerase), which is necessary for the +RNA to be translated into DNA, which can then be incorporated into the host’s genome as a provirus.
After integration of the retrovirus into the cellular genome, a reverse transcriptase inhibitor is added to the cell. Will the production of the new viruses be blocked?
No. the +RNA genome can still be translated by host ribosomes
Are retroviruses required to carry the enzyme reverse transcriptase?
No. Although some retroviruses do carry the enzyme, it is not required, as the + RNA already encodes for reverse transcriptase and can directly be translated by ribosomes
dsDNA viruses often have large genomes that include genes for enzymes involved in deoxyribonucleotide synthesis and DNA replication. Given the limited information that viruses may contain in their genomes, why carry around genes for an enzyme possessed by the host?
The host cell will only make dNTPs in preparation for replication. If the virus wants to reproduce without waiting for the host to do so, it must encode its own enzymes for the synthesis of DNA building blocks.
Why do dsDNA viruses, but not RNA viruses, carry enzymes for (d)NTP synthesis?
the host cell is always performing transcription and therefore always has NTPs present in the cell that the virus can use.
the host cell will only produce dNTP during times of replication and, therefore, the virus must carry these enzymes if they want to reproduce without waiting for the host to do so. it must encode its own enzymes for the DNA building blocks
What is a prion?
an infectious protein that has an ability to self replicate
these proteins do not have any RNA or DNA, any membrane structures, or any organelles
What are transmissible spongiform encephalopathies?
Refers to prion diseases in mammals that cause degeneration of nervous tissues, ultimately leading to loss of coordination, dementia, and death. These are usually passed by consumption of prion diseased meat.
-side note: incubation period for prion diseases can be several months to several years in animals and humans
What are viriods?
- short circular pieces of RNA that are virus like, but do not have capsids. Therefore, in order for viroids to infect host cells, they must be coinfected (uses other viruses’ capsids).
- Viroids also don’t code for proteins; rather they act like miRNAs and siRNAs to block translation. Viroids hijack the cell’s enzymes for their own replication.
- viroids are mostly associated with infecting plants
what is the classification of bacteria that has: 1) one flagella, 2) 2 flagellas on opposite sides, and 3) bacteria that are just generally covered in flagellas?
1) monotrichous
2) amphitrichous
3) peritrichous
What’s the difference between gram + and gram - bacteria
gram + bacteria have a very thick cell wall, which means they have a lot of peptidoglycan
gram - bacteria have a very thin cell wall, and thus have little amounts of peptidoglycan
Which types of bacteria can create endospores?
gram +
This is because the spores cell walls are made of a thick peptidoglycan layer, which is only produced in gram + bacteria
Which type of bacteria has an inner membrane, a thin cell wall, and an outer membrane?
gram - bacteria
