A biochemist isolates and purifies various molecules needed for DNA replication. When she adds these molecules to DNA, replication occurs, but half of the DNA produced consists of a normal DNA strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture

DNA ligase

Explanation:

The biochemist must have left out DNA ligase enzyme.

The DNA ligase enzyme is able to catalyze the formation of phosphodiester bonds and as such, capable of joining strands of DNA together to form a single strand.

The numerous DNA segments of a few nucleotides long observed by the biochemist must have been the replicated product of the lagging DNA strand. The lagging strand is replicated discontinuously in short strands because the DNA polymerase enzyme can only elongate primers in 5' to 3' direction. The short segments are known as Okazaki segments and are usually joined together to form a whole strand by the DNA ligase enzyme.

Hence, the missing component is the DNA ligase.

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