Micro Exam 4 Virus - a genetic element that contains either RNA or DNA surrounded by a protein capsid and that replicate only inside host cells Obligate intracellular parasite - Cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses Capsid - the protein shell that surrounds the genome of a virus Nucleocapsid - nucleic acid + protein in enveloped viruses Envelope - viruses have an outer layer consisting of a phospholipid bilayer (from host cell membrane) and viral proteins – those without envelope are easier to kill Virion – inactive form of virus outside the host cell Capsomere - identical protein subunits that spontaneously self-assemble into a finished capsid icosahedron – one of 2 types of capsids (the other is helical) Genome - the sum total of the genetic information carried by an organism Bacteriophage - “bacteria eating” viruses that infect bacteria Temperate phage: Undergo adsorption and penetration, do not undergo replication or release immediately Viral DNA enters a Prophage state Inserted into bacterial chromosome → Copied during normal bacterial cell division Induction - prophage in a lysogenic cell becomes activated and progresses directly into viral replication and the lytic cycle lysogeny - a condition in which the host chromosome carries bacteriophage DNA lysogenic conversion - when a bacterium acquires a new trait from its temperate phage: Corynebacterium diphtheriae – diphtheria toxin Vibrio cholerae – cholera toxin Clostridium botulinum – botulinum toxin Monolayer - single, confluent sheet of cells that supports viral multiplication Plaques - areas where virus-infected cells have been destroyed show up as clear, well-defined patches in the cell sheet
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