[Campbell Biology P.383] A student isolates, purifies, and combines in a test tube a variety... | Practice Question
A student isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?
Explanation
The description of 'numerous segments of DNA a few hundred nucleotides long' on the newly synthesized strand is characteristic of Okazaki fragments, which are produced on the lagging strand during DNA replication. The fact that these segments are present but not continuous suggests that the enzyme responsible for joining them is missing. DNA ligase is the enzyme that forms phosphodiester bonds to connect Okazaki fragments, creating a continuous new DNA strand.