B. DNA ligase uses the energy of ATP to close nicks in DNA and this involves a m
ID: 558411 • Letter: B
Question
B. DNA ligase uses the energy of ATP to close nicks in DNA and this involves a mechanism which includes A. an AMP in a phospho-ester linkage to the 5'-hydroxyl at one side of the nick an AMP in a phosphor-anhydride linkage to the 5'-phosphate at one side of the nick C. an AMP in a phosphor-anhydride linkage to the side-chain of a tyrosine in DNA ligase D. an AMP in a phospho-ester linkage to the 3'-hydroxyl at one side of the nick E. a linkage of the side-chain of a tyrosine in DNA ligase to the 5'-phosphate at one side of the nick Cells normally delay replication until DNA damage and replication errors have been repaired because A. DNA polymerase cannot function when the DNA is damaged B. Replication of damage or mismatched DNA results in mutations C. It is not possible to do repair and replication at the same time D. Some repair may require recombination, and that cannot be done during replication Chromatin decompaction is a preliminary step in gene expression. How is chromatin decompacted? (discussed these enzymes involved, DNA structures, describe type of interactions).Explanation / Answer
The correct answer is an option B, i.e. an AMP in a phosphor - anhydride linkage to the 5' - phosphate at one side of the nick.
Explanation: The sealing of nicks between adjacent residues of a single-strand break on a double-strand substrate and the joining of double-strand breaks are enzymatically catalyzed by DNA ligases. The formation of a phosphodiester bond between the 3' hydroxyl and 5' phosphate of adjacent DNA residues proceeds in three steps: Initially, the ligase is self-adenylated by reaction with free ATP. Next, the adenyl group is transferred to the 5'-phosphorylated end of the "donor" strand. Finally, the formation of the phosphodiester bond proceeds after reaction of the adenylated donor end with the adjacent 3' hydroxyl acceptor and the release of AMP.
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