Question

_________ cut(s) DNA molecules at specific sites. a. DNA polymerase c. Restriction enzymes b. DNA probes d. DNA ligase

Short answer

c. Restriction enzymes

Step-by-step solution

Understand the options

Let's review what each of the given options does to determine the correct answer. This will help in identifying which one is responsible for cutting DNA at specific sites.

Evaluate DNA Polymerase

DNA polymerase is an enzyme involved in DNA replication. It synthesizes DNA strands by adding nucleotides to a pre-existing chain but does not cut DNA.

Evaluate DNA Probes

DNA probes are short strands of DNA used to detect the presence of complementary sequences through hybridization. They do not cut DNA; instead, they bind to specific DNA sequences.

Evaluate Restriction Enzymes

Restriction enzymes are enzymes that cut DNA at specific sequences, known as restriction sites. They recognize particular nucleotide sequences and make cuts in the DNA strand.

Evaluate DNA Ligase

DNA ligase is an enzyme that facilitates the joining of DNA strands together by forming phosphodiester bonds. It is not involved in cutting DNA; rather, it helps in DNA repair and replication.

Determine the Correct Answer

Having reviewed all options, the only enzyme that cuts DNA at specific sites is the restriction enzyme. Therefore, the correct answer is c. Restriction enzymes.

Key concepts

DNA Replication

DNA replication is a vital process that occurs in all living organisms to ensure that each new cell receives a full set of genetic material. During replication, the DNA molecule unwinds and separates into two strands, acting as templates for the creation of new complementary strands.

• Role of DNA Polymerase: Once the DNA strands are separated, DNA polymerase plays a crucial role in adding nucleotides to the growing strand. This enzyme reads the existing DNA strands and matches them with complementary nucleotides, step-by-step, to form new DNA strands.
• Initiation: Before DNA polymerase starts its work, a primer is required to initiate the process. This primer is a short strand of RNA that provides a starting point.
• Elongation: DNA polymerase then extends from the primer, adding nucleotides in a continuous chain. In one strand (the leading strand), this occurs in a smooth sequence, while in the other (the lagging strand), it happens in small sections known as Okazaki fragments.
• Proofreading: DNA polymerase also has a proofreading ability, ensuring accuracy by removing incorrectly paired nucleotides.

As a result, two identical DNA molecules are produced, each consisting of one old strand and one new strand, ensuring genetic consistency.

DNA Probes

DNA probes are incredibly useful tools in molecular biology. These short, single-stranded segments of DNA or RNA are used to locate particular sequences within a DNA sample, ensuring that scientists can identify genes of interest or detect mutations.

• Hybridization Process: DNA probes function by hybridization, a process where they bind, or "hybridize," to complementary DNA strands in a sample. This binding is highly specific, meaning the probe will only attach to sequences that match its own sequence.
• Labeling: For detection, probes are often labeled with radioactive or fluorescent tags. These tags allow scientists to visualize the binding of the probe to the DNA and identify the presence of specific sequences within the sample.
• Applications: DNA probes are used in various technologies, including Southern blotting, to study gene expression, or in medical diagnostics to detect pathogens or genetic disorders.

Through the precise binding of probes, researchers can gain detailed insights into the genetic information and function of DNA within biological samples.

DNA Ligase

DNA ligase is an essential enzyme for DNA repair and replication, especially important for joining together parts of DNA. It works by linking together the sugar-phosphate backbones of DNA strands through the formation of phosphodiester bonds.

• Function in Replication: During DNA replication, DNA ligase is crucial for the lagging strand, where Okazaki fragments are produced. It links these fragments to create a continuous strand.
• Repair Mechanisms: DNA ligase plays a pivotal role in repairing breaks in the DNA strand, preventing mutations, and maintaining genetic stability.
• Biotechnological Uses: In laboratories, DNA ligase is often used in genetic engineering for gene cloning, where it helps in recombining DNA by joining together DNA fragments from different sources.

Without DNA ligase, cells would struggle to maintain their genetic integrity, making its role in repair and replication indispensable.