MicroBio Flashcards
what is an obligate intracellular parasite?
this is the definition of a virus
obligate - relies on host
intracellular - must enter the hosts cells
true or false, some viruses can make ATP
false - viruses cannot perform any sort of chemical reactions –> need host machinery.
some viruses may carry host ATP within their capsids
t or f, a virus can contain both DNA and RNA in its genome
false - viruses only contain one kind of nucleic acid in their genome 99% of the time
what is a bacteriophage
a virus that infects bacteria
explain the viral genome size. what is the consequence of this?
the genome size is very small as its packed tightly into the viral capsid which is non-pliable. one consequence of tis is that the viral genome is polycistronic (more than one protein per gene) –> multiple reading frames
what is helical vs polyhedral? what is the head, tail fibres, base plate, and sheath?
helical - rod like capsid
polyhedral - multiple-sided capsid
head - capsid which holds nucleic acid
tail fibres - bind the cell surface and press the base plate onto it
sheath - uses stored ATP to contract and inject nucleic acid into the cell
why do bacteriophages inject their genomes while animal viruses do not (in general)?
bacteria have cell walls which must be penetrated.
animal cells don’t and thus, he virus can be internalized naturally.
what is budding and what is an envelope?
some viruses are enveloped in which they acquired a membrane around themselves from the previous host cell. the process of a virus moving through a PM and taking some membrane with it is called budding.
t or f, all plant viruses and bacteriophages are naked viruses (non-enveloped).
true - since enveloped viruses do not inject their genomes which must be done to penetrate the cell wall
what is
- attachment / adhesion
- penetration / eclipse
for bacteriophages
- attachment of virus to the cell based on specific proteins in the cells capsid (or envelope for animal viruses)
- eclipse is the actual entrance of the genome via injection
the lytic cycle:
once infected, the virus is immediately transcribed / translated. what is the product of an important early gene
hydrolase is created - this degrades host DNA.
the lytic cycle: why is hydrolase important?
hydrolase provides free dNTP’s that can be used for viral DNA replication
the lytic cycle: once DNA replication has occurred + translation of Capsid proteins (etc.) what is an important late gene produced and what does it do?
lysozyme is produced which is an enzyme that degrades cell walls –> this breaks the bacterial cell wall and causes it to lyse (lytic cycle)
if a virus was cultured in cells with radio labeled cysteine and phosphate, which of these two molecules will be found in the next cell the virus infects.
- cysteine will be incorporated into the initial capsid proteins
- phosphate will be incorporated into the nucleic acid
the next cell will be injected with phosphate-rich nucleic acid but the capsid remains on the outside.
The lysogenic cycle of phages: the lytic cycle is problematic since it kills of all of its host cells. what is a prophage and a lysogen?
prophage - this is when the viral genome integrates with the host genome
lysogen - a bacterium with viral genome integrated in its own genome
The lysogenic cycle of phages: t or f, once in the host DNA, the viral segment gets replicated and transcribed over and over again.
false
- it does repeatedly get replicated as the bacterium performs replication
- it is dormant in terms of Tx. this is allowed since a repressor protein sits on its promoter site
The lysogenic cycle of phages: what is excision?
when the prophage leaves the host genome. now it can enter the lytic cycle
What is transduction?
when the prophage is excised from the host genome, it may inaccurately do this and bring along some host DNA with it. Sometimes this DNA carries a full trait / gene and thus introduces a new phenotype for the next bacteria that is infected
what receptor does gp120 of HIV bind?
CD4 of T cells
t or f, some viruses carry with them and use host proteins.
true –> e.g. when budding occurs, the virus brings with it all embedded proteins
what is uncoating?
when an animal virus enters a cell via endocytosis, the capsid must be removed to expose the genome.
what is an animal viruses productive cycle?
animal viruses exhibit lytic, lysogenic, and productive cycles –> this is the lytic cycle except it does not kill the cell at the end since it buds via exocytosis.
what is a provirus?
a prophage but for animal viruses
explain RNA (+) viruses in terms of
- what there genome is
- what they must bring / encode
- how their Tx / Tl / replication occurs
- there genome is a + sense strand of mRNA meaning they can be directly translated by host cell enzymes.
- Translation can occur immediately, but no host cell can Tx or replicate RNA –> therefore, RNA (+) viruses must encode RNA-dependent RNA polymerase.
replication: to make more + strands of the RNA genome, the RNA polymerase first makes a (-) strand and then uses this new template to create many (+) strands.
why does it mean when we say a genome is infective?
it is an RNA (+) strand since it can be directly translated
