chapter 19 Flashcards
What are viruses?
small, non-cellular infectious particle consisting of genes packaged in a protein coat and, sometimes, a membrane
Why aren’t viruses considered to be alive?
They do not consist of cells, cannot reproduce or metabolize outside of a host cell
What are capsids?
the protein shell that encloses the viral genome
What is the function of the capsid?
to hold the viral nucleic acid
What is a viral envelope?
A membrane that surrounds the capsids of influenza viruses and many other viruses found in animals; they contain a combination of viral and host cell molecules
What are viral envelopes derived from?
from membranes of host cells
Give an example of a virus that has an envelope.
influenza
What is a bacteriophage?
Viruses that infect bacteria
Describe the appearance of a phage.
have an elongated capsid head that encloses their DNA and attached to the protein tailpiece; it is the tail piece that attaches the bacteriophage to the host and injects its DNA inside
Describe the general life cycle of a virus.
The virus enters the host cell and the nucleic acid and capsids separate. Once a viral genome has entered a cell, the cell begins to manufacture viral proteins, using host enzymes, ribosomes, tRNAs, amino acids, ATP, etc. The nucleic acid is replicated to produce copies of the viral genome and transcribed/translated to produce more capsomeres. These products self-assemble into new virus particles which then exit the cell.
The lytic cycle
results in the death of the host cell; The lytic cycle produces new phages and lyses (breaks open) the host’s cell wall, releasing the progeny viruses
The lysogenic cycle
the viral DNA molecule is incorporated into the host cell’s chromosome without destroying the cell as a prophage; Every time the host divides, it copies the phage DNA and passes a copy to daughter cells
What is a virulent phage?
A phage that reproduces only by the lytic cycle
What is a temperate phage?
Phages that use both the lytic and lysogenic cycles
What is a prophage?
the viral DNA molecule is incorporated into the host cell’s chromosome without destroying the cell
