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27 Cards in this Set

  • Front
  • Back
What are virus' that infect bacteria?
*cause most diseases that plague industrialized world
What is a virus in an extracellular state?
Describe it.
-protein coat (capsid) surrounding nucleic acid
-some have phospholipid envelope
-outermost layer provides protection and recognition sites for host cells
What happens once a virion becomes an intracellular state?
-capsid removed
-virus exists as nucleic acid
What is the traditional definition of viruses?
-viruses are obligate, intracellular parasites
-can not carry out any metabolic parasites
-neither grow nor respond to environment
-can not reproduce independently
-no cytoplasmic membrane, cytosol, organelles
-they are harmful for the host
What is the contemporary definition of viruses?
-viruses transmit information from cell to cell
-genetic analysis suggests viruses co-evolved with cells, never independent
-most viruses are harmless, if not beneficial
How are virus' classified?
-by the genetic material they contain
-also: kinds of cells they enter, size of virus, nature of capsid coat, shape of virus, presence or absence of envelope
Describe the genetic material of bacteriophages.
-linear or circular
-composed of single or multiple segments
What hosts do bacteriophages like?
-most viruses are specific for particular kinds of host cells
-some viruses may only infect particular cell in host (such as HIV on T cells)
*generalists infect many kinds of cells in many different hosts
What is the smallest virus?
Next in size?
Largest two?
-Bacteriophage MS2, bacterial ribosomes and poliovirus
-bacteriophage T4
-tobacco mosaic virus and small pox virus
What are capsids?
-protein coats that provide protection for viral nucleic acid and means of attachment to host's cells
-composed of protein subunits called capsomeres; single or multiple types
What shapes do capsids have?
-helical; tobacco mosaic virus
-polyhedral (icosahedron); rhinovirus
-complex; smallpox virus
What are some basic bacteriophage structures?
- (I)X174
- M13
- lambda
- T7
- T4
- P1
What is an evelope on viruses?
-acquired from host cell during viral replication or release
-portion of membrane system of host
-composed of phospholipid bilayer and proteins (some proteins are virally-coded glycoproteins (spikes))
-envelopes proteins and glycoproteins often play role in host recognition
*coronavirus and togavirus
How do you assemble a bacteriophage T4?
-mature head
-tail fibers
-mature virion
How does a bacteriophage T4 replicate?
-enter by depositing phage DNA
-bacterial chromosome degraded
-release by lysis
Why are bacteriophages specific in their ability to infect a host bacterium?
-phage attachment (receptors)
-host restriction and modification
Describe phage attachment.
-phage usually interact with bacteria through a specific receptor
*if receptor is present, bacteria is sensitve to phage
What are two problems with page attachment
-bacterial host range mutants have mutations in receptors
-phage host range mutants have altered tail fibers
*so you have a mutant bacterium and phage
Who came up with host restriction and modification?
When did he win the Nobel prize?
-Werner Arber in 1979
Can bacteria compete for their own bacteriophage?
-can distinguish between bacteriophage grown in itself versus another bacteria; then it destroys foreign bacteriophage
How do bacteria dinstinguish between bacteriophages and what is done after recognition?
-recognizes it by its methylation pattern
-destroys foreign bacteriophage using restriction endonucleases
How do you calculate E.O.P?
-efficiency of plating= PFU per plate / # phage particles per plate
What are some bacteriophage strategies for altering host functions?
-modification of host RNAP transcription
-modification of phage RNAP transcription
-degradation of host DNA
-synthesis and use of altered nucleotides
-degradation of host deoxynuvleotides
-inhibition of host DNA synthesis
-capture of host dnaB protein
What are some characteristics of bacteriophage strategies for altering host functions?
-the larger the genome of the phage, the more ways it can modify host functions for its own benefit
-this is because of the larger capacity to encode useful proteins; the phage becomes less dependent on host functions for its survival (ie: DNA polymerases, RNA polymerases)
What is a prophage?
-the phage DNA integrated into bacterial chromosome
-prophage can be excised (induction) upon physical or chemical stress such as UV light, X-rays, mutagens-undergoes lytic cycle
What is lysogeny?
-alternate lifestyle in which bacteriphage genome is integrated into host genome
-can be lysogenic or temperate phages
What are the two paths bacterium can take when infected with lysogenic Lamba virus'?
-attachment and entry
1) synthesis, assembly, release through lysis
2) prophage enters bacterial chromosome, replication of chromosome (and progeny) cell division, further cell division, induction, synthesis, assembly, release through lysis