Microbiology Chapter 13
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What is a virion?
nucelic acid surrounded by a protein coat
What is a capsid?
the protein coat
What is a nucleocapsid?
A capsid with enclosed nucleic acid
What is an enveloped virus?
A virus with a lipid bilayer outside of the capsid
What is a naked virus?
- A virus that is not enveloped
- Most phages
What are the 3 different shapes of viruses?
What does an Icosahedral Virus look like?
20 flat triangles, resembles a soccer ball
What does a helical virus look like?
Appears cylindrical, nucleic acid is in a helix
What does complex virus look like?
Has a complicated structure
What is an arboviruse?
- spread by arthropods
- ex mosquitos
What is the Lytic phage infections model?
What is a lytic/virulent phage?
- exits host at end of infection cycle via lysing
- a productive infection
What are the 5 steps of a T4 (lytic/virulent) infection cycle?
- Genome Entry
- Synthesis of Phage proteins and genome
What occurs during the T4 attachment phase?
- phage collides with host cell by chance
- attaches to a receptor/pilus on cell that would normally be used for other functions
What occurs during the T4 genome entry phase?
- post-attachment phage injects it's DNA/RNA into the cell via it's tail degrading a bit of the cell wall with lysozyme
- After nucleic acid is injected the capsid remains on the cell's surface
What occurs during the T4 Synthesis of phage proteins and genome phase?
- T4 genes are transcribed and translated quickly
- Proteins are synthesized to hijack the cells processes
- Proteins are synthesized to create the phage parts
What occurs during the T4 Assembly phase?
once all components are synthesized they are assembled into new phage particles with the help of scaffolds
What occurs during the T4 release phase?
the phage encoded enzyme lysozyme is produced and degrades the cell wall from the inside out causing the cell to lyse
What occurs during Temperate Phage infections?
The can be lytic or lysogenic
What is the difference between a lytic infection and a lysogenic infection?
- lytic is a productie infection
- lysogenic is a latent infection
What occurs during a lysogenic infection?
- phage's DNA becomes integrated into host's DNA
- host is called a prophage
What are the consequences of lysogeny?
- immunity to superinfection
- lysogenic conversion
What prevents gene excision in a prophage?
What is immunity to superinfection>
- The same phage cannot reinfect a prophage
- the repressor which maintains the lysogenic state will repress the incoming phage
What is lysogenic conversion?
modification of host's properties resulting from expression of phage DNA integrated into the host
What is an example of a temperate infection?
What is a filamentous phage?
- looks like long fibers
- causes productive infections that slow down reproduction
What is an example of a filamentous phage?
What occurs during M13 filamentous infection?
attaches to F pilus and injects itself into cytoplasm where it is synthesized and replicated
What is transduction?
the transfer of DNA via a phage
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