Saliva is a poor growth medium for bacteria due to
a. the presence of lysozyme.
b. the presence of mucus.
c. lack of nutrients.
d. lack of available oxygen.
Answer: a. the presence of lysozyme.
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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.
Which types of cells in the human body do not repair themselves if they have been damaged?
a. Skin b. Bone c. Blood d. Hair e. Nerve
The alternate complement pathway uses complement proteins C1, C2, and C4.
Answer the following statement true (T) or false (F)
Which of the following activities is not a way that unicellular organisms maintain homeostasis?
A. Reproduction B. Growth C. Response to the environment D. Cell specialization