Explain how, when improper base pairing escapes repair by the proofreading system, cells are able to detect and repair
mutations. What will be an ideal response?
ANSWER: Improper base pairing distorts the structure of DNA, and repair enzymes scan the DNA and
recognize these distortions. Once the distortion is recognized, these repair enzymes cut the
DNA strand on either side of the mismatched nucleotide, removing a portion of the DNA
strand. DNA polymerase then fills in the gap, and another enzyme closes up the sugarphosphate
backbone.
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True kidneys have tubules called ____
a. nephrons b. hepatic tubules
c. metanephridia d. Malpighian tubules e. protonephridia
The greatest mass extinction of all time occurred at the end of the ____ era, in which more than 90% of all existing
marine organisms became extinct. a. Archaean b. Paleozoic c. Cenozoic d. Mesozoic e. Proterozoic
what digestive enzymes are produced by the small intestine
What will be an ideal response?
DNA is methylated on which nucleotides?
A) cytosine B) thymine C) uracil D) guanine E) adenine