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14 Cards in this Set

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What is a virus particle (Virion)?
infectious form of virus that exists outside host and facilitate transmission from one host to another
What is a virion composed of?
Nucleic acid genome surrounded by protein coat and in some cases a lipid membrane layer
What are characteristics of a viral genome?
DNA/RNA
double or single stranded
Mostly linear
very specific
Size range=0.02 to 0.3 um
What is a capsid?
protein shell that surrounds the genome of a virus particle: Composed of capsomeres arranged in repetition around nucleic acid genome
What is a capsomere
Protein subunit of rapid
Nucleocapsids are highly symmetric. What are types of symmetry?
Helical symmetry: rod shaped virus (ex. tobacco mosaic virus)

Icosahedral symmetry: spherical viruses
What enzymes do virions contain?
1) Lysozyme: lyse bacterial cell wall
2) Nucleic acid polymerases: For replication of viral genome, not dsDNA
What is a titer?
Number of infections units per volume of fluid
What is efficiency of plating?
Number of plaque forming units always lower than microscope counts:
-inactive virions
-mutant genomes
-conditions not appropriate in lab for infectivity
Phases of viral replication?
1) Attachment (adsorption)
2) Entry
3) Synthesis
4) Assembly
5) Release
What mechanisms do bacteria contain to diminish viral infection?
1) CRISPR: similar to RNA interference
2)Restriction-modification system: effective against dsDNA virus, restriction enzymes cleave DNA, Modifies host own DNA to prevent cleavage of own DNA
Characteristics of early viral proteins?
-synthesized soon after infection
-necessary for replication of virus nucleic acid
-typically act catalytically
-made in small amounts
Characteristics of late viral proteins?
-synthsized later
-include proteins of virus coat
-typically structural components
-made in larger amounts
!Special modification in Phage T4 DNA?
contains modified base: 5-hydrozymethylcytosine, DNA is resistant to most restriction enzymes!