1.5 The Cell- Viruses and Subviral Particles Flashcards
Why are viruses ‘obligate intracellular parasites’?
They cannot replicate on their own. They require a host cell.
They do not have ribosomes.
What is positive and negative sense.
What must negative sense have to work?
This is about RNA
Positive Sense : implies that the genomes may be directly translated into functional proteins by the ribosome of the host cell, just like mRNA
Negative Sense-the negative sense RNA strand acts as a template for synthesis of a complementary strand, which can then be used as a template for protein synthesis. MUST CARRY RNA REPLICASE
What is the lytic and lysogenic cycle?
Lytic cycle: bacteriophage maximizes use of cell’s machinery without regard for survival of the cell. Very virulent because if they cause the cell to explode, they will release the virions which will infect other cells.
Lysogenic Cycle: virus integrates into genome as provirus or prophage. May stay in the DNA indefinitely, or external factors (radiation, light, or chemicals) may cause the provirus to revert to lytic cycle.
When provirus is present in the genome, it is generally less susceptible to superinfection by another virus, which may be advantageous.
How do prions cause disease?
What are examples?
They are infectious proteins.
Trigger misfolding of other proteins
Switch proteins from an alpha structure to a beta-pleated sheet, which reduces the ability of the cell to degrade the protein. Since it is unable to be degraded, it interferes with cell function.
Mad Cow disease, Crutzfeldt-Jakob disease, and familial fatal insomnia are examples in humans.
How do viroids cause disease?
Viroids infect plants.
Small, circular RNA
They can silence genes in the plant genome, resulting in metabolic disruption
Generally only in plants, however Hepatitis D is an example of a viroid that causes disease.
Describe the pathway of retroviral nucleic acids form infection of a host cell to release of viral progeny.
- infect host.
- Translocation of genetic location to correct area of cell
- DNA viruses must enter nucleus to be transcribed into mRNA
- mRNA goes to cytoplasm
- if positive sense, just stays in cytoplasm to be translated into proteins
- Using ribosomes of host cell, viral RNA is translated into protein, such as new capcids.
What is the genetic material in a virus composed of?
Genetic information may be: circular or linear
Single or double stranded
Can be DNA or RNA
What is a capsid?
What is the envelope?
Is it weak or strong?
Capsid: Its the protein coat that surrounds the virus,
May be surround by an envelope composed of phospholipids and virus-specific proteins.
The envelope is very sensitive to heat, detergentes, and desiccation, making it easy to kill. Those that don’t have an envelope are more resistant to sterilization.
What are virions?
These are the progeny cells of viruses, that are made when the virus attacks a cell and replicates.
What are the structure of the bacteriophage?
Bacteriophage- viruses that attack bacteria
Capsid: outer coat
Nucleic acid: in the capsid
Tail sheath- acts like a siringe
Tail fibers- help to identify and stabilize the bacteriophage and connect it to the right host cell
Not all cells use this method to enter cells. Some enter by endocytosis, or through cell walls, or through cell pores.
What are retroviruses? How do they work?
What’s an example of one.
They are single stranded RNA viruses.
They make DNA from the RNA using reverse transcriptase
The DNA integrates into the host cell genome
It is then replicated like it’s its own DNA of the host.
In essence 1. RNA, 2. DNA using reverse transcriptase, 3. DNA gets into host cell, 4. DNA is replicated by host.
The only way to remove the virus is to kill the cell. HIV is an example
T or F: All viruses can infect all cells.
False- they must have a specific receptor to attack a cell.
How are viruses released from the cell? (x3)
- Cell death (apoptosis) that causes all contents to be release
- The sheer number of virions may cause the cell to burst (lysis)
- Extrusion- they exit using the plasma membrane, leaving the host cell intact. This is good, because the virus can continue to use the DNA. This is also called a productive cycle
