Problem 1 - Biology Today and Tomorrow with Physiology

Question

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

Step-by-Step Solution

Answer

c. Restriction enzymes

Step 1: Understanding the Terminology

To solve this problem, it's important to first understand what each option refers to. DNA polymerase is an enzyme that synthesizes new DNA strands. DNA probes are single-stranded DNA sequences used to detect the presence of complementary sequences by hybridization. Restriction enzymes, also known as restriction endonucleases, are enzymes that cut DNA at specific sequences. DNA ligase is an enzyme that joins DNA fragments together.

Step 2: Identifying the Correct Function

The question asks which option cuts DNA molecules at specific sites. We now need to focus on the function of cutting DNA. Among the options provided, only restriction enzymes are known for cutting DNA molecules at specific sequences. This process is crucial in various biotechnological applications, such as molecular cloning.

Step 3: Verifying the Answer Choice

Given our understanding from Step 2, we confirm that restriction enzymes match the description provided in the question. The other options do not function as cutting enzymes. DNA polymerase synthesizes DNA, DNA probes facilitate sequence detection, and DNA ligase joins DNA fragments.

Key Concepts

DNA Polymerase

DNA polymerase is an essential enzyme in the replication of DNA. It functions by adding nucleotides to a growing DNA strand during DNA replication. This process occurs in a specific direction, from the 5' end to the 3' end of the DNA strand. The enzyme reads the template DNA strand and adds complementary nucleotides, ensuring that the new strand is an accurate copy of the original.

DNA polymerase requires a primer to start its task. A primer is a short nucleic acid sequence that provides a starting point for DNA synthesis. Once the primer binds to the template strand, DNA polymerase can elongate the DNA strand by adding nucleotides one by one.

• Crucial role in DNA replication.
• Adds nucleotides to the 3' end of the strand.
• Works with a primer for synthesis initiation.

Without DNA polymerase, cells would not be able to replicate their DNA, which is a fundamental process required for cell division and reproduction.

DNA Probes

DNA probes are short, single-stranded DNA sequences used in laboratories to detect the presence of complementary nucleotide sequences in a sample. They are commonly used in various molecular biology techniques, such as Southern blotting or fluorescence in situ hybridization (FISH).

Probes are labeled with a detectable tag, which can be a radioactive isotope, a fluorescent dye, or an enzyme. This labeling allows scientists to visually identify whether hybridization, which is the pairing of the probe with its complementary DNA, has occurred. When the probe binds to its target sequence, the attached label provides a signal that indicates the presence of the specific DNA sequence in the sample.

• Used for sequence detection and identification.
• Work by hybridizing to complementary DNA.
• Labeling allows for easy detection of hybridization signals.

DNA probes are valuable tools in genetic research, diagnostics, and forensics, offering precise identification of specific DNA sequences.

DNA Ligase

DNA ligase is an enzyme that plays a vital role in DNA replication and repair. Its main function is to "glue" DNA fragments together, forming a continuous strand. This is essential during DNA replication, where the lagging strand is synthesized in short segments called Okazaki fragments.

Once these fragments are formed, DNA ligase catalyzes the formation of phosphodiester bonds between them, thus joining the fragments into a single, cohesive strand. This process ensures the integrity and stability of the DNA molecule.

• Joins DNA fragments in replication and repair.
• Facilitates the connection of Okazaki fragments.
• Essential for DNA molecule stability and continuity.

In genetic engineering, DNA ligase is also utilized to insert foreign DNA into vectors or plasmids, making it indispensable in cloning and biotechnological applications.