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27 Cards in this Set
- Front
- Back
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What are virus' that infect bacteria?
animal/human? |
-bacteriophage
-virus *cause most diseases that plague industrialized world |
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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 |
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What happens once a virion becomes an intracellular state?
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-capsid removed
-virus exists as nucleic acid |
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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 |
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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 |
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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 |
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Describe the genetic material of bacteriophages.
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-dsDNA
-ssDNA -dsRNA -ssRNA -linear or circular -composed of single or multiple segments |
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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 |
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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 |
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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 |
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What shapes do capsids have?
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-helical; tobacco mosaic virus
-polyhedral (icosahedron); rhinovirus -complex; smallpox virus |
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What are some basic bacteriophage structures?
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- (I)X174
- M13 - lambda - T7 - T4 - P1 |
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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 |
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How do you assemble a bacteriophage T4?
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-base
-tail -sheath -DNA -capsid -mature head -tail fibers -mature virion |
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How does a bacteriophage T4 replicate?
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-attach
-enter by depositing phage DNA -bacterial chromosome degraded -synthesis -assembly -release by lysis |
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Why are bacteriophages specific in their ability to infect a host bacterium?
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-phage attachment (receptors)
-host restriction and modification |
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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 |
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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 |
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Who came up with host restriction and modification?
When did he win the Nobel prize? |
-Werner Arber in 1979
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Can bacteria compete for their own bacteriophage?
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-can distinguish between bacteriophage grown in itself versus another bacteria; then it destroys foreign bacteriophage
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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 |
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How do you calculate E.O.P?
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-efficiency of plating= PFU per plate / # phage particles per plate
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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 |
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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) |
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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 |
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What is lysogeny?
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-alternate lifestyle in which bacteriphage genome is integrated into host genome
-can be lysogenic or temperate phages |
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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 |
