Exam 1: Viruses Flashcards
A virus is a ___ surrounded by a _____. Some viruses are also surrounded by a ___
nucleic acid
protein coat
Membranous coat
A viruses genome can consist of ____. The genome is usually organized as ____
double/single D/RNA
a single linear or circular molecule of nucleic acid, may consist of multiple molecules of nucleic acid
A capsid is the protein shell enclosing the viral genome. They are built of protein subunits called
capsomeres.
Viral envelopes are ___ they contain
membranous structures that help viruses infect hosts. They contain contain host cell phospholipids and membrane proteins. They also contain proteins and
glycoproteins of viral origin
Bacterio/phages are
Viruses that infect bacteria, and contain some of the most complex capsids.
The host range of the virus is
the number of host species a virus can infect
Many DNA viruses use the DNA
polymerases of the host cell to synthesize new genomes along
the templates provided by the viral DNA. In contrast, to replicate their genomes, RNA viruses
use virally encoded RNA
polymerases that can use RNA as a template.
After the viral nucleic acid molecules and capsomeres are
produced, they
they self-assemble into new viruses
The simplest type of viral replicative cycle ends with
the exit of
hundreds or thousands of viruses from the infected host cell,
a process that often damages or destroys the cell
Describe the lytic cycle of a phage
A phage replicative cycle that culminates in death of the host
cell
A phage that replicates only by
a lytic cycle is a
virulent phage
They lysogenic cycle
allows replication of phage without destroying the host
Phages capable of both the lytic and lysogenic cycles are known as
temperate phages
One prophage gene codes for a protein that
prevents transciprtion of most of the other prophage genes, making the genome silent within the bacterium
Prophages are capable of generating active phages that lyse their host cells. This occurs when
the alpha genome is induced to exit the bacterial chromosome and initiate a lytic cycle
give a general overview of the CRISPR Cas system
if a phage infects a bacterial cell, its DNA is integrated into the genome between two repeat sequences
RNA is processed into short strands, which binds to a cas protein, forming a complex.
Complementary RNA binds to DNA from the invading phage. Cas protein then cuts phage DNA.
The DNA molecule is degraded
If the cell survives infection, any further attempt by the phage to infect the cell triggers CRASPR region transcription
Natural selection favors phage mutants that can
bind to altered receptors or are resistant to enzymes
There are only a few bacteriophages that have an envelope or RNA genome, Animal viruses have___
an envelope or RNA genome
How does an animal virus enter a host cell?
The envelope/outer layer
viral glycoproteins bind to surface cell receptors
Animal viruses make viral glycoproteins by
Ribosomes bound to
the endoplasmic reticulum (ER) of the host cell make the pro-
tein parts of the envelope glycoproteins; cellular enzymes in the
ER and Golgi apparatus then add the sugars.
These viral glycoproteins are then transported to the cell surface
New viral capsids are wrapped in membrane as they bud from the cell in animal viruses in a process much like
exocytosis
The RNA animal viruses with the most complicated replica-
tive cycles are the____ These viruses have
an enzyme called_____
retroviruses
reverse transcriptase
Reverse transcriptase transcribes
an RNA template into a DNA copy, an RNA—>DNA flow
Give a general overview of the HIV replicative cycle. Note that it is a retrovirus
Viral proteins and RNA are released into the cytoplasm and catalyze reverse transcriptase synthesis of viral DNA.
The new viral DNA enters
the cell’s nucleus and integrates into a chromosome.
The integrated viral DNA, called a provirus, never leaves the host’s genome.
viral proteins synthesized in the cytosol envelope glycoproteins made in the ER and Gogli and vesicles transport them to the surface to cover the membranous coat.
The RNA polymerase of the host transcribes the proviral DNA into RNA molecules.
The RNA molecules produced by reverse transcriptase can
can function both as mRNA for the synthesis of viral proteins and as genomes for the new viruses that will be assembled and released from the cell.
A provirus never leaves the hosts genome. In contrast,
a prophage leaves the hosts genome at the start of a lytic cycle
What is a provirus
Integrated viral DNA within a hosts genome produced during retrovirus replicative cycle
Most molecular
biologists favor the hypothesis that viruses originated from
naked bits of cellular nucleic acids that moved from one cell to
another, perhaps via injured cell surfaces.
