Mbio Chapter 6
24.What is the signal for a prophage to become lytic?
A stress response or whenever the cell becomes unhealthy
What is the basic structure of a virus? What is the function of these pieces?
Capsid (to protect DNA or RNA) and infective nucleic acids (DNA or RNA)
.What is the capsid? What is it made of?
Capsid may be enclosed in an envelope composed of a membrane from the host cell A protective protein shell. May be enclosed in a spiked envelope composed of phospholipid membrane taken from host cell with tegument layer in between envelope and capsid which may contain proteins. Spikes help attach the envelope to the capsid of the virus to the host cell.
23.What is a prophage?
Hidden virus DNA inserted into host DNA that replicates with the host
What is the host range? Do viruses all have the same host range?
Host range: some viruses can only infect one species (ex: HIV), some can infect many (ex: west nile), some can infect only one but then mutate to infect another (ex: swine flu).
.How can genomic information become part of a virus?How is this information transformed to other hosts?
If viruses go through lysogeny, they can insert their DNA into the host DNA creating a prophage (integrated phage genome) that is hidden and is replicated every time the host cell replicates. Transduction: an accident where a virus takes some of the host DNA and leaves some of the virus DNA when excising itself from the host. When this virus travels to a new host and integrates itself, creating a new prophage, it can give the old host DNA to the new. Other than mutation, this is how antibiotic resistance is spread.
27.What is the role of CRISPR in microbial defense
It is a pseudo-immune system where the cell remembers the viral DNA by inserting into its own genome so that it can be recognized and cleaved by enzymes that look to cleave DNA without methyl markers
Why is it difficult to come up with antiviral therapies?
It is difficult to create antiviral medicine because they often utilize our own cellular machinery, making attacks on them attacks on ourselves.
22.Understand the difference between and what happens in the lytic vs. lysogenic cycle.
Lytic cycle Attachment and insertion ds DNA cyclizes to circular DNA Host DNA is cleaved, cell synthesizes capsid proteins Cell replicates phage DNA DNA is packaged Phage lyses cell via enzymes Lysogenic cycle - temperate phage intermediate of lytic cycle When cell is healthy the virus circular DNA is inserted into cell DNA (prophage). Replicates with the cell, hidden When cell is unhealthy the virus is excised and cleaves DNA, returning to lytic cycle
What are viral plaques?
Plaques are regions in a bacterial lawn where a virus has lysed a cell and its burst phages have infected the cells directly surrounding the first bacteria to lyse. They appear empty, as this is where no living bacteria exists.
.What is the size of a virus relative to a bacterium?
Range greatly in size. Most are smaller but there are a few larger than bacteria.
How are viruses beneficial?
Recycle nutrients in marine ecosystems, they are the dominant predator that lyse bacteria releasing carbon back into the ecosystem. Phage therapy to treat pathogenic bacterial infections
26.What is slow release? How is this different from a lytic virus?
Slow release - not all viruses can do this An unfavorable compromise where the virus reproduces and exits the cell without lysing it. ss DNA is template for ds DNA that are made, packaged, and exit the envelope. The host cell still reproduces, but slower as most of its nutrients go towards replicating the virus.
25.What is transduction?
Transfer of DNA between virus and host cell, which can be passed on to new host cells
20.What must occur for a virus to infect a host? What happens once it has infected the host?
Viral infection includes: 1. Recognize host and attach - Cell surface receptors - Virus has evolved to bind to a protein important for cell function and use for cell access 2. Genome entry (infection) -Sometimes entire virus -Sometimes just genome (bacteriophage creates ghost) 3. Assembly of virions (hijack of host cell machinery) Replicates phage DNA Packages DNA to make new viruses 4. Exit and transmit (lyse)
How have viruses impacted human populations? How Do they impact the agricultural industry?
Viroid: nucleic acid infectious particle that infects plants and travels through the plant plasmodesmata to infect other adjacent plants.
What are viroids?Prions?
Viroids: nucleic acid = infection particle; moves from cell to cell and causes disease; no capsid - Mainly RNA based mainly infecting plants -Can move through plasmodesmata so doesn't need a capsid -NO capsid = NOT a virus Prions: infection agent ONLY with protein -NO Nucleic Acid = NOT a virus -Mad cow disease, can be infection or arise from host mutation (alzheimer's) -Misfolded proteins aggregate together (cluster) and causes cell death -Misfolded proteins attach to normal proteins and cause it misfold too -Hydrophobic facing outward -Unaffected to nucleic acid treatments --UV radiation --Nucleases
What types of organisms are susceptible to viral infections?
Viruses infect all domains of life.
How is a virus able to maintain so many fewer genes than a bacterium?
Viruses utilize their hosts to do reproduce Fewer necessary genes. Capsid - Protective protein shell filled with viral genome Enzyme - viral specific Envelope proteins - help anchor that envelop to the virus Infective nucleic acids
3.What is a virus?
a non-cellular particle that must infect a host cell so that it may reproduce. Singlar particles are virions.
Are viruses all the same size?
no
What is a bacteriopvirushage?
that only infects bacteria.