Multiple Choice
Why is it important for a cell to efficiently repair its DNA?
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14. DNA Synthesis
DNA Repair
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How does DNA ligase join Okazaki fragments during DNA replication?
A
By forming a phosphodiester bond between the 3'-OH end of one fragment and the 5'-phosphate end of the next fragment
B
By unwinding the DNA double helix at the replication fork
C
By removing nucleotides from the ends of the fragments
D
By adding RNA primers between the fragments
Verified step by step guidance1
Understand the context: DNA replication involves the synthesis of new DNA strands. On the lagging strand, DNA is synthesized discontinuously in short segments called Okazaki fragments. These fragments need to be joined together to form a continuous strand.
Identify the role of DNA ligase: DNA ligase is an enzyme responsible for joining the Okazaki fragments. It does this by creating a covalent bond between the fragments, specifically a phosphodiester bond.
Examine the chemical reaction: DNA ligase catalyzes the formation of a phosphodiester bond between the 3'-hydroxyl (3'-OH) group of one fragment and the 5'-phosphate (5'-P) group of the adjacent fragment. This reaction requires energy, which is typically provided by ATP or NAD+ depending on the organism.
Clarify what DNA ligase does not do: DNA ligase does not unwind the DNA double helix (this is the role of helicase), remove nucleotides (this is the role of exonucleases), or add RNA primers (this is the role of primase). Its specific function is to seal nicks in the sugar-phosphate backbone of DNA.
Summarize the process: DNA ligase ensures the integrity of the lagging strand by sealing the gaps between Okazaki fragments, forming a continuous DNA strand. This is a critical step in DNA replication to maintain the stability of the genetic material.
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