Determine the correctness of [a] Dam methylase protects E. coli DNA from phage endonucleases; and [r] E. coli Dam methylase methylates the adenosine residue in GATC.
Both [a] and [r] are true and [r] is the correct reason for [a].
Both [a] and [r] are true but [r] is not the correct reason for [a].
Dam methylase modifies adenine in GATC, so the reason is true. Dam has roles including strand discrimination for mismatch repair and regulation of replication. The assertion incorrectly identifies its role as protection from phage endonucleases; that is not the stated Dam function, and restriction–modification distinctions matter. The keyed choice is D: assertion false, reason true.
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