A biochemist 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?
a. DNA polymerase
b. DNA ligase
c. Okazaki fragments
d. Primase

Verified step by step guidance

Understand the process of DNA replication, which involves the synthesis of a new DNA strand complementary to the template strand. This process requires several enzymes and components.

Recognize that during DNA replication, the leading strand is synthesized continuously, while the lagging strand is synthesized in short segments known as Okazaki fragments.

Identify the role of DNA ligase in DNA replication. DNA ligase is responsible for joining the Okazaki fragments on the lagging strand, creating a continuous DNA strand.

Consider the problem description: the DNA molecules consist of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. This suggests that the Okazaki fragments are not being joined together.

Conclude that the absence of DNA ligase in the mixture is likely the reason for the presence of unjoined Okazaki fragments, as DNA ligase is needed to connect these fragments into a continuous strand.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

DNA Replication

DNA replication is the process by which a cell duplicates its DNA, ensuring that each daughter cell receives an exact copy of the genetic material. It involves unwinding the double helix, synthesizing new strands using existing strands as templates, and requires various enzymes and proteins to facilitate the process.

Okazaki Fragments

Okazaki fragments are short sequences of DNA nucleotides synthesized discontinuously on the lagging strand during DNA replication. These fragments are later joined together by DNA ligase to form a continuous strand, as DNA polymerase can only synthesize DNA in the 5' to 3' direction.

DNA Ligase

DNA ligase is an enzyme crucial for DNA replication and repair, responsible for joining Okazaki fragments on the lagging strand. It catalyzes the formation of phosphodiester bonds between adjacent DNA fragments, ensuring the continuity and integrity of the newly synthesized DNA strand.