Students working in pairs or small groups receive a simulated virus: two paper cups taped together, enclosing a strip of paper listing an RNA or DNA sequence (an abbreviated viral genome). The students break open the cups (simulating viral uncoating in the host cell) and decide how host and/or viral enzymes will convert the genome into viral proteins and new genomes. The sequences provided describe a double-stranded DNA virus, single-stranded RNA viruses (+ or - strand), a retrovirus, and a double-stranded RNA virus. Templates for photocopying the genomes, sample worksheets, and an instructor’s answer key are included.