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Direct Repair (Quiz 2)

How stable is the DNA molecule? The structure of DNA makes it a very stable molecule. The hydrogen bonds between complementary strands protect the most reactive parts of the molecule. DNA is a large and complex molecule and interactions between the external environment and DNA can lead to chemical changes. Frequently these changes are the result of exposure to radiation or to chemicals. In addition to damage such as breaks in the DNA or the loss of parts of the sequence there can also be more subtle changes. These changes may not directly affect the function of DNA but may increase the probability of a mutation in the future. Despite its stability, DNA is vulnerable to errors and systems to detect these errors and repair them are necessary.

View the animation below, then complete the quiz to test your knowledge of the concept.






1Thymine dimers are mutations that are commonly caused by
A)X-rays.
B)UV light.
C)heat.
D)antibiotics.
E)disinfectants.



2The enzyme ________ catalyzes thymine dimer repair.
A)DNA isomerase
B)DNA ligase
C)DNA photolyase
D)DNA phosphatase
E)DNA transferase



3The enzyme methylguanine-DNA methyltransferase
A)removes entire guanine residues and replaces them with methyl groups.
B)removes methyl groups from the oxygen attached at the 6-position of guanines.
C)removes methyl groups from the nitrogen attached at the 6-position of guanines.
D)adds methyl groups to the oxygen attached at the 6-position of guanines.
E)adds methyl groups to the nitrogen attached at the 6-position of guanines.



4The repair of a thymine dimer using light involves the splitting of the dimer and reformation of the two thymines.
A)True
B)False



5Chemical agents can induce mutations.
A)True
B)False







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