A biochemist isolated and purified molecules needed for dna replication. Whne she added some dna, replictation occursd but the dna molecules were defective. Each consisted of a normal dna strand paired with numerous segments of dna a few hundred nucleotides long. What had she probably left out of the mixture?

She left Ligase enzyme out of the mixture.

Explanation:

DNA replication is the process of formation of new molecules of DNA from the existing one. This process occurs in semiconservative way i. e each new strand consist of one newly synthesised strand and one old parent strand that act as template for the formation of new strand. replication on one strand occurs continuously from 5 prime to 3 prime but on other strands it occurs discontinuously from 5 prime to 3 prime because DNA polymerase moves only in one direction from 5 prime to 3 prime. Hence in discontinuous strands gaps remained. These gaps are filled by Ligase enzyme.

Requirements for DNA replication:

DNA replications needs

Primers

DNA Polymerase enzyme

DNA helicase enzyme

Single nucleotide binding protein

dNTPs

and Ligase enzyme.

Correct choice:

She left Ligase enzyme out of the mixture.