Viruses  are  made  up of nucleic
   acid  (DNA  or RNA) enclosed in a protein coat (capsid), which is made
   up of subunits called capsomeres. Bacterial viruses are called phages.
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<lI> Tobacco Mosaic Virus has a helical capsid enclosing RNA.
<lI> Adenoviruses have a polyhedral capsid with glycoprotein spikes.
<lI> Flu  viruses  have  8  capsids  with  an  RNA  genome wrapped in a
membranous envelope embedded with glycoproteins.
<lI> Phage T4 has a polyhedral head and a tail apparatus.
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   Review:  <A ClAsS=ACT Href="http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/activities/load.html?18&amp;A" oNClick="popact('http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/activities/load.html?18&amp;A');txtcolor('virus1','gray');return false;" Id=virus1><iMg sRc="/images/tutorial.gif" aLt='' boRDer=0></A>