Microbiology quiz 3

Describe the process of generalized transduction

1. Lytic phage infects a target cell and causes DNA to fragment 2. lytic phage incorporates bacterial chromosomal DNA into its phage head 3. this phage can infect another bacteria 4. the DNA it carried can be incorporated into the host chromosome via homologous recombination

Lysogen

A bacterium that carries phage DNA (a prophage) integrated into its genome

Which components would you find in all viruses?

A capsid and proteins

Temperate phage

A phage that is capable of reproducing by either the lytic or lysogenic cycle. Makes lysogen immune to superbugs (infection by the same phage)

Would you expect a transducing phage to reproduce in a host? Why or why not?

A transducing phage would not reproduce in a host because the virus is injecting bacterial DNA into the cell, not viral DNA. Bacterial DNA does not have the genetic information that encodes for viral replication so it would not happen. Instead, the bacterial cell uses homologous recombination to insert the DNA into its genome. The daughter cells will have this new DNA, and will not produce viruses.

What is a viral receptor and why is this a poor term?

A viral receptor is a protein receptor on the cell's membrane that the viral proteins can bind to and then allow it to enter the cell. It is a poor term because it makes it seem as though the receptor is there specifically for the virus. However, the membrane receptors can be channels, pores, pumps, or ligand binding proteins.

Enveloped virus

A virus enclosed within a phospholipid membrane derived from its host cell.

Explain why the transfer of DNA in Hfr conjugation is often incomplete.

An Hfr cell is one where the plasmid recombines into the main chromosome. When this cell attempts to do conjugation it often is incomplete because the cell does not have enough time to fully transfer its whole genome. This is because this is a very fragile process and the cells can get knocked around from each other. What results is the recipient cell having some of the donor's DNA, and it is integrated into the cell's chromosome by homologous recombination

Viral spikes

Attach specifically to host cell receptors

Animal virus replication (enveloped virus)

Attachment: spikes of a vision attach to specific host cell receptors Membrane Fusion: envelope of vision fuses with cytoplasm Nucleocapsid release: nucleocapsid is released into the cytoplasm, viral envelope remains part of the cytoplasmic membrane Uncoating: nucleic acid separates from capsid Synthesis: nucleic acids and proteins

How does generalized transduction differ from the lytic cycle?

Differs because as the viruses are coming together, some will envelope broken pieces of cellular DNA that will be incorporated into the capsid which creates a transdusing particle

Synthesis

Expressin of viral genes to produce viral structural and catalytic genes like capsid proteins and enzymes required for replication

F' cell description

F' cell: When an incorrect excision of the integrated F plasmid brings along a portion of the chromosome, generating an F' cell

F+ cell description

F+ cell: Bacteria that contain an F plasmid which helps them in the conjugation process for the exchange of genetic material

Viral matrix proteins

Give the virus its shape, only present in enveloped viruses

Hfr cell description

Hfr cell: when the F plasmid recombines with the main chromosome, which allows the chromosomal DNA to be transferred during conjugation

How is generalized transduction similar to a normal lytic replication cycle?

It begins the same with a virus inserting its DNA into a host cell, destroying the host cell's genome, and then creating more viruses.

To be considered a virus, a virus must..

Only replicate inside of a host's cytoplasm

Capsid

Outer protein coat of a virus

What is specialized transduction?

Part of the bacterial DNA adjacent to the incorporated viral DNA becomes part of the virus that will take it to another bacterial cell. It's called specialized because it's always typically the same part of the DNA. Some of the viral DNA is also left within the host cell's genome. This makes every phage produced inside this cell ineffective, and no other phages will be produced by these phages when they infect a host cell.

Lytic phage

Phage attaches to specific receptors on the cell wall, tail contracts and phage DNA is injected into the bacterial cell leaving the phage coat outside. Phage genome is transcribed and phage proteins are synthesized. Phage DNA is replicated and host DNA is destroyed. Phage components are assembled and then the cell lyses and phages are released

If you are analyzing the DNA sequence of a non-pathogenic E. coli bacterium and notice that it has a gene that is most similar to another pathogenic strain of E. coli. Upon further analysis, there are no other flanking genetic sequences that have been transferred... just the gene. Which of the following modes of HGT could explain this result? Explain your reasoning.

Specialized transduction Generalized Transduction Transformation Conjugation between HFR and F- For specialized and conjugation, it could happen if only the bacterial chromosomal DNA was incorporated and not the viral genes or the F plasmid genes

Which stage of the viral replication cycle (attachment, uncoating, entry, synthesis) best explains why bacteriophage do not infect human cells?

The attachment phase best describes why the bacteriophage can only infect bacteria. Viruses can only infect cells that have very specific proteins on their membrane. If the cell doesn't have the proteins that the virus can bind to then the virus will not bind to the cell. Human cells do not have the same membrane proteins as bacteria do, which explains why bacteriophages can't infect human cells.

Which type of bacteriophage is most similar to a chicken pox virus: T4 or lambda? Explain your reasoning in terms of their respective life cycles.

The chicken pox virus has a latent phase within the human body where it does not show any symptoms. This means that it is most similar to the lambda life cycle since lambda will have a latent phase, while T4 will go immediately to the lysing phase of the cell.

Which component of an enveloped virus is directly involved with attachment to a host cell?

The envelope

Bacteriophage vs eukaryotic phage

The genome, but not the protein coat, enters the cell

Prophage

The viral DNA that is embedded in the host cell's DNA

Exit of enveloped viruses

They exit through budding and that is how they get their envelope. In this way the cell can still be alive after the virus has left it

Exit of bacteriophages

They lyse the cell and kill it in order to exit the cell.

Suppose a bacteriophage infected a mutant E. coli cell that is unable to perform homologous recombination

Transducing phage has some of the bacterial DNA that is mistakenly encapsulated. So yes it could form for generalized. No for specialized because specialized has to do with homologous recombination

Which of the following mechanisms is most likely the explanation of how N. gonorrhoeae acquired human DNA? A. Transformation B. Conjugation C. Transduction

Transformation: this is because conjugation can only occur between two bacterial cells, not between a eukaryotic cell and a bacterial cell. Transduction is not an option because viruses can't infect both a eukaryotic cell and a bacterial cell. They are too specific to infect both types of cells so it would be impossible to have gene transfer this way. The most likely is transformation because gonorrhoeae kills human cells they likely picked up naked human DNA from the environment

Lysogenic infection

Type of infection in which a virus embeds its DNA into the DNA of the host cell and is replicated along with the host cell's DNA. It is silent and does not produce any affects while this is occurring. Can return to a phage and continue the lytic cycle. This will occur when the cell has damage to its DNA

Lysogenic conversion

When a bacterium acquires a new trait from its temperate phage

What are the advantages of phage therapy?

When someone is infected with a bacteria that is resistant to antibiotics it can be beneficial to use phage therapy because the bacteriophages will kill only the bacteria and not affect the human tissue. The bacteriophage will have specificity that will only allow it bind and kill only the bacteria.

Specialized transduction

a highly specific part of the host genome is regularly incorporated into the virus

Which viral type has a genome that can be directly translated?

ds DNA ss (+) DNA ss (-) DNA ss (+) RNA

Non-enveloped viruses COULD have

protein spikes Single stranded DNA Single stranded RNA Double stranded DNA

Enveloped viruses COULD have .... (check all that apply)

protein spikes matrix protein Single stranded DNA Single stranded RNA Double stranded DNA A phospholipid bilayer

A virus that has which type of genome must carry replicase within the viral particle?

ss (-) RNA

Why are Hfr cells able to cause a "high frequency of recombination" in the recipient cell

they have the F plasmid incorporated into their own genome which causes them during rolling circle replication, the plasmid will get transferred and so will part of the main chromosome, the main chromosome will very likely be similar or identical on the corresponding DNA in the recipient. So since it is similar it will have a high frequency of homologous recombination since they are the same/similar. Increased genetic exchange.