biochem 012 DNA and protein synthesis part 6 (watson crick griffith chargoff's rule translation
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where are viral envelopes derived from and what is the chemical composition of the envelopes? where on the virus are they found?
viral envelopes, which are derived from the host cell's membrane, contain a combination of viral and host cell molecules. the viral envelopes surround the capsids of certain viruses
what type of virus has the most complex capsids found among viruses?
describe the structure of phages
phages have an elongated capsid head the encloses their DNA and a protein tail piece that attaches the phage to the host and inject the phage DNA inside
what does it mean to say that viruses are obligate intracellular parasites?
this means that they can only reproduce within a host cell
what is the host range?
a limited number of host cells that a virus can infect
true or false? viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses
what are the two types of reproductive mechanisms of phages?
lytic cycle and lysogenic cycle
what are restriction enzymes?
bacteria have defenses against phages, including restriction enzymes that recognize and cut up certain phage DNA
what is a virulent phage?
a phage that reproduces only by the lytic cycle
describe the lytic cycle.
the lytic cycle is a phage reproductive cycle that culminates in hte death of the host cell. The lytic cycle produces new phages and digests the host's cell wall, releasing the progeny viruses
what are temperate phages?
these are phages that use both the lytic and lysogenic cycles
describe the lysogenic cycle
the lysogenic cycle replicates the phage genome without destroying the host. The viral DNA molecule is incorporated into the host cell's chromosome. Every time the host divides, it copies the phage DNA and passes the copies to daughter cells. An environmental signal can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode.
what is a prophage
viral DNA that is integrated in the host chromosome during the lytic cycle is called a prophage
where do viruses with viral envelopes get their envelopes from?
some viral envelopes are formed from the host cell's plasma membrane as the viral capsids exit. Other viral membranes form from the host's nucleear envelope and are then replaced by an envelope made from Golgi apparatus membrane
what do viral glycoproteins on viral envelopes do?
viral glycoproteins on the envelope bind to specific receptor molecules on the surface of a host cell
the broadest variety of RNA genomes is found in viruses that infect _______
what is a provirus?
viruses with RNA genomes integrate their viral DNA into the host genome--this viral DNA is referred to as a provirus. Unlike the prophage, the provirus remains a permanent resident of the host cell. The host's RNA polymerase transcribes the proviral DNA into RNA molecules. The RNA molecules function both as mRNA for synthesis of viral proteins and as genomes for new virus particles released from the cell
viruses evolved from...
bits of cellular nucleic acid. candidates for the source of viral genomes are plasmids, circular DNA in bacteria and yeasts, and transposons, small mobile DNA segments. However, there is controversy about whether this virus evolved before or after cells.
what is the largest virus yet discovered
mimvirus, a double-stranded DNA virus, is hte largest virus yet discovered
what are viriods?
they are circular RNA molcules that infect plants and disrupt their growth. they lack a capsid
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