Microbiology Flashcards
To determine whether a pathogen is bacterial or viral, what microscopy methods can be used?
Because viruses are significantly smaller than bacteria, they require electron microscopy. Therefore, is a pathogen is observed using light microscopy, it can be concluded that, between a bacteria or virus, it must be a bacteria.
What are the two enzymes produced by bacteriophage viruses during the lytic cycle and what are their functions?
There are two enzymes produced by bacteriophages during the lytic cycle, one in early phase and the other in the late phase. HYDROLASE is synthesized during the early phase to degrade the host genome, supplying dNTPs to the virus. LYSOZYME is synthesized during the late phase to lyse the cell allowing the virus particles to escape.
What is the main difference between enveloped and nonenveloped viruses in regards to their effect on the host cell?
Enveloped viruses bud off the host cell’s membrane, leaving the cell in tact. In contrast, unenveloped viruses cause the host cell to burst as it leaves.
Application: It can be determined experimentally whether a virus has an envelope or not. If the cells are infected, and none of the cells rupture over time, it can be concluded that the viruses are transmitting between cells via envelope.
What are the 5 phases of bacteriophage infection?
- Landing: phage TAIL recognizes specific bacterial receptors
- Pinning: TAIL bend, BASE PLATE with its PINs come into contact with the cell surface and bind.
- Lysozyme
- Penetration of hollow tube located in tail sheath
- Injection of genetic material
If clathrin-coated receptor mediated endocytosis is blocked, which types or viruses are prevented from infection a host animal cell?
Clathrin-coated receptor mediated endocytosis allows for the entry of naked (unenveloped) and enveloped viruses. Enveloped viruses differ from naked viruses in that they can infect cells via a clathrin-independent method (fusion with the plasma membrane).
If a host cells ribosomes or ATP production is blocked, can a virus use that cell to propagate itself?
No. Viruses are known as obligate intracellular parasites. They rely on host cell machinery to self replicate since they are not able to do this outside of the cell.
An example of this concept would be the application of cyanide to a cell which inhibits the electron transport chain. Since no ATP would be synthesized any longer, the host cell machinery would stall, preventing virus replication and transcription and translation.
How can a single and double stranded viruses be differentiated? How can an RNA and DNA virus be differentiated?
Analyzing the base pair ratio and content is a method to differentiated between single and double stranded and RNA/DNA viruses. If the base pair ratio is NOT 1:1, as in the case of double stranded nucleic acids, it can be said that this virus is single stranded. If uracil is present in, the virus must be an RNA virus.
How is the virus able to contain such a short genome but encode multiple proteins required for its replication and propagation?
Multiple reading frames
Can a phage or plant virus be enveloped?
No. Bacteria have peptidoglycan cell walls and plants have cellulose cell walls both of which prevent budding. Therefore, all bacterial and plant viruses are naked viruses.
If a phage viral capsid is radio-labeled as in the second step in the Hershey Chase experiments, will the capsid be found inside the bacterial cell?
No, the capsid becomes ECLIPSED to the cell while the genetic material penetrates the membrane. However, if phage genetic material is radiolabeled as in the first step of the Hershey Chase experiments, the bacteria will express radio labeled material.
Where are RNA and DNA containing viral genomes located in the host cell?
Only DNA viruses can enter the nucleus of the host cell. The only RNA virus that can enter the nucleus are retroviruses. DNA viruses also have the option to remain within the cytoplasm, but if so, they must carry their own DNA polymerases. RNA viruses are localized to the cytoplasm.
What are the two key enzymes that retroviruses must posses in order to propagate?
Retroviruses (mRNA+) must 1) encode for RNA-dependent DNA polymerases (reverse transcriptase) and 2) integrase to randomly add the viral DNA in the host’s genome
If a certain virus is packaged without an RNA-dependent RNA polymerase, which RNA virus is it, mRNA+ or mRNA-?
RNA viruses must either a) carry their own RNA-dependent RNA polymerases or b) encode RNA-dependent RNA polymerases for replication of their own genomes since no cell contains polymerases that synthesizes RNA FROM RNA. mRNA+ needs to CODE for RNA-dependent RNA polymerases while mRNA- viruses must CODE AND CARRY RNA-dependent polymerases
How do bacteria differentiate between their own genome and viral genomes?
Methylation of bacterial genome.
What are the steps of viral-directed transduction of genetic material?
- Infection and host cell DNA degradation
- Accidental packaging of host cell fragmented DNA with viral progeny
- Infection to another cell
- Incorporation of fragmented DNA into new host cell genome via homologous recombination
What are the major and minor names of bacteria that differ based on shape?
Major: Cocci (round), bacillus (rod), Spirillus (spiral)
Minor: eubacteria and archea (extremophiles)
