chapter 19 Flashcards
(23 cards)
what is a virus?
an infectious particle consisting of genes packaged in a protein coat
what are bacteriophages?
viruses that infect bacteria
what is the structure of viruses?
very small infectious particles consisting of nucleic acid, enclosed by protein coat and in some cases membranous envelopes
what are viral genomes?
DNA virus: double or single stranded DNA
RNA virus: double or single stranded RNA
what is a capsid?
protein shell enclosing viral genome
what are capsomeres?
the protein subunit that builds capsids, can be helical, or icosahedral viruses
what are membranous envelopes?
assist in infection
what are viral envelopes?
surround capsids of influenza and others in animals
what is the most complex capsid?
bacteriophages
what is host range?
the number of host cells that can infect
how do viruses replicate?
obligate intracellular parasites; can only replicate within host cell
what are bacteria defenses?
restriction enzymes that recognize and cut up phage DNA
what are the general features of viral replicative cycles?
viral genome enters host cell in a variety of ways, once viral genome has entered a cell, the cell begins to manufacture viral proteins, virus makes use of host enzymes, ribosomes, tRINAs, amino acids, ATP, and other molecules and viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses
what is the lytic cycle?
phage cycle with host cell death that produces new phages and lyses, releasing progeny viruses
what is a virulent phage?
a phage using only the lytic cycle
what is the lysogenic cycle?
phage genome replicating without destroying the host
what is a prophage?
viral DNA incorporated in the host chromosome
what are temperate phages?
phages using lytic and lysogenic cycles (called lambda λ)
what are the phases of the lytic cycle?
- attachment
- entry of phage dna & degradation of host dna
- synthesis of viral genomes & proteins
- self-assembly
- release
what are retroviruses?
use reverse transcriptase to copy their RNA genome into DNA (HIV is a retrovirus that causes AIDS)
what is a provirus?
viral DNA integrated into the host genome. unlike prophage, provirus remains a permanent resident of the host cell
