In E. coli, the adenine in the sequence GATC is methylated by the Dam enzyme. In the same cells a restriction endonuclease recognizes and cleaves dsDNA with GATC on either strand. Why does E. coli have these two enzymes?
A) The enzymes cut the E. coli genome into pieces that bind to viral particles and inhibit viral replication.
B) The enzymes increase the rate of mutation and genome rearrangement, thus increasing the likelihood that E. coli cells will mutate and become resistant to viral infection.
C) The enzymes encourage lysogeny because the cleavage sites are recognized by viral integrases.
D) The enzymes protect E. coli from infection by preferentially degrading viral or other exogenous DNA that is not methylated.
Answer: D
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Lysogeny refers to
A. the latent state of herpes infections. B. virions exiting host cell. C. altering the host range of a virus. D. the viral genome inserting into bacterial host chromosome.
Eyes in different animal groups arose independently many times,
A. and the genes triggering lens formation in these different groups are homologous. B. and the genes triggering lens formation in these different groups are homoplastic (analogous). C. and the genes triggering lens formation in these different groups are examples of divergent evolution. D. and the genes for eye color are multivariate. E. and the genes for the eyes themselves are divergent.
A relationship in which one partner benefits and the other is harmed is termed
A. commensalism. B. parasitism. C. independence. D. mutualism.
A paraphyletic group contains
A. a common ancestor but not all of its descendants. B. groups of species with different common ancestors. C. a common ancestor and all of its descendants. D. a common ancestor and all of its descendants but not the most recent common ancestor. E. every species ever derived from a common ancestor.