Recombinant DNA technology involves combining genes from two sources, such as different species, into a single molecule.

Applying restriction enzymes to DNA will cleave the DNA into fragments, which can be isolated for specific genes. Ligase can then be used to fuse the fragments together into a full recombinant gene.

Topoisomerase is responsible for relieving tension in the winding of the DNA helix. DNA polymerase synthesizes new DNA from individual nucleotides, but would not be useful in fusing two types of DNA together.

Helicases are enzymes that separate annealed strands of nucleic acids. This function provides the single-stranded template used in replication.

Primase is responsible for adding DNA primers, DNA polymerase I scans for mismatched nucleotides and mutations, and ligase repairs breaks in the DNA backbone.

Polymerase chain reaction, or PCR, is commonly used in laboratories to increase the amount of a small biological sample. Given a small sample of DNA, the process replicates the sample to make numerous identical copies. These copies can then be studied directly, used to make protein products, or incorporated into genetic modification.

Other laboratory techniques can be used to achieve the results given by the other answer options.

DNA topoisomerases are the cell's solution to the "winding" problem. The double helical nature of DNA results in tension during the replication process that would interfere with the process. DNA topoisomerases cut the phosphate backbone to relieve this tension, and allow DNA to replicate properly.

Primase is an enzyme that is essential for the process of DNA replication. It synthesizes RNA primers so that DNA polymerase may begin replicating DNA. Mutation to the gene that codes for primase would damage the protein. Without primase, a cell would not be able to go through the process of replication because DNA polymerase would not properly bind the DNA.

RNA polymerase is responsible for transcribing DNA and helicase is responsible for unwinding the DNA double stranded helix.

The lagging strand exists because DNA is antiparallel and replication always occurs in the 5' to 3' direction. One strand of DNA will be replicated in the 5' to 3' direction toward the replication fork, following in the same direction as the DNA is "unzipped." This is the leading strand, which can be replicated fluidly. The lagging strand is oriented in the 3' to 5' direction, and must be read backward (away from the replication fork).

Having a lagging strand does not help the cell conserve energy. DNA is a polyanion, but this is due to the phosphate groups in the backbone. If anything, having a lagging strand actually makes it more difficult to maintain a similar rate of replication between strands since they cannot be replicated in the same direction.

Okazaki fragments are the cell’s solution to replicating DNA in the opposite direction of the replication fork. They are small fragments of DNA synthesized on the lagging strand. While the leading strand can be continuously synthesized toward the replication fork, the lagging strand must be made in small pieces opposite from the replication fork.

Using small fragments of RNA to silence genes is a process known as RNA interference. DNA that has been cleaved by nucleases is not related to Okazaki fragments. Single-strand binding proteins are small proteins used to prevent DNA from reannealing during replication.

DNA ligase is an enzyme responsible for repairing nicks in the sugar-phosphate backbone of DNA and for fusing Okazaki fragments during DNA replication. It accomplishes this task by resynthesizing the phosphodiester bonds that hold the backbone together

The other answers describe the functions of other proteins involved in DNA replication or DNA transcription. Helicase is responsible for unwinding double-stranded nucleic acids and is essential for producing the replication fork during DNA synthesis. Primase synthesizes RNA primers as attachment points for DNA polymerase during replication. RNA polymerase is responsible for transcribing a DNA template into RNA products.

DNA is replicated in a semiconservative manner. This implies that each parental strand serves as the template for a newly replicated strand. Each daughter DNA helix is thus composed of one complete parental strand and one complete new strand.

Parent: (PP)

Replication: (PD)(DP)

The other answer choices refer to other theories of DNA replication, which have since been proven incorrect.

Conservative replication results in a newly synthesized molecule of DNA that does not contain either parental strand. Each daughter helix would be composed of only parental strands or only new strands.

Parent: (PP)

Replication: (PP)(DD)

Random and dispersive actually refer to the same process, and imply that DNA is replicated such that the resulting strands are made up of bits and pieces of both newly replicated DNA and the parental DNA. Neither strand is fully conserved in this theory of replication, and instead two hybrid strands are produced.

An adenine-thymine sequence would be more likely to be found near the replication origin. Adenine and thymine pair with two hydrogen bonds, while cytosine and guanine pair with three hydrogen bonds. This makes adenine and thymine regions easier to break apart. Since helicase must break the hydrogen bonds in order to create the replication fork at the replication origin, it makes sense that this event would occur in a region where there were weaker forces between the two DNA strands.

Remember, guanine always pairs with cytosine and adenine always pairs with thymine.