Bio1100 Chapter 19 Prokaryotes: The First Single-Celled Creatures
  1. Viruses are intracellular              and can reproduce only within         cells.
    • •
      Viruses are made up of nucleic acid genome (DNA or RNA) enclosed in a protein coat called a capsid.
      Some bacterial viruses (phages) have a head consisting of a capsid and a DNA genome. Tobacco Mosaic Virus has a helical capsid enclosing its RNA genome. HIV (human immunodeficiency virus) has 2 RNA molecules; a membranous envelope wraps a capsid and enzymes. Quiz
     
  2. The human immunodeficiency virus (HIV) is a               that can exist as a             in human white blood cells.
    • • HIV is a retrovirus with a RNA genome.

      1. A virus infects white blood cells (macrophages and T cells) by binding to cell receptors and injecting its RNA together with a few enzymes.

      2. The viral enzyme reverse transcriptase copies the RNA genome into DNA, which is integrated into the host DNA where it is called a provirus.

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      Quiz


    • • HIV replication.

      1. Eventually the proviral DNA is transcribed into RNA molecules, which may serve both as mRNA for synthesis of viral proteins and as new viral genomes.

      2. The proteins and RNA assemble into new virus particles and exit the host cell.