MMG Bacteriophage
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What are virus' that infect bacteria?
animal/human? -
-bacteriophage
-virus
*cause most diseases that plague industrialized world -
What is a virus in an extracellular state?
Describe it. -
-virion
-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?
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-capsid removed
-virus exists as nucleic acid - What is the traditional definition of viruses?
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-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?
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-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?
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-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.
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-dsDNA
-ssDNA
-dsRNA
-ssRNA
-linear or circular
-composed of single or multiple segments - What hosts do bacteriophages like?
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-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?
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-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?
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-helical; tobacco mosaic virus
-polyhedral (icosahedron); rhinovirus
-complex; smallpox virus - What are some basic bacteriophage structures?
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- (I)X174
- M13
- lambda
- T7
- T4
- P1 - What is an evelope on viruses?
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-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?
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-base
-tail
-sheath
-DNA
-capsid
-mature head
-tail fibers
-mature virion - How does a bacteriophage T4 replicate?
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-attach
-enter by depositing phage DNA
-bacterial chromosome degraded
-synthesis
-assembly
-release by lysis - Why are bacteriophages specific in their ability to infect a host bacterium?
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-phage attachment (receptors)
-host restriction and modification - Describe phage attachment.
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-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
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-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?
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-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?
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-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?
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-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?
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-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?
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-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'?
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-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