Which molecule reads the DNA sequence and adds complementary nucleotides using the base pair rules?
The correct answer and explanation is:
Correct Answer: DNA polymerase
DNA polymerase is the enzyme responsible for reading the DNA sequence and adding complementary nucleotides according to base-pairing rules during DNA replication. It plays a key role in ensuring that the genetic information is copied accurately before cell division.
During DNA replication, the double helix of DNA is first unwound by another enzyme called helicase. This creates two single strands that serve as templates. DNA polymerase attaches to one of these single strands and begins to read the sequence of nitrogenous bases. According to the base pairing rules, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). As DNA polymerase moves along the template strand, it matches each base with its complement and adds the appropriate nucleotide to form the new strand. For example, if the template strand has a sequence A-T-C-G, DNA polymerase adds T-A-G-C to the growing complementary strand.
DNA polymerase also has proofreading ability. As it adds new nucleotides, it checks to ensure that each one is correctly paired. If it detects a mismatch, it removes the incorrect nucleotide and replaces it with the correct one. This proofreading function reduces the chances of mutations during DNA replication.
There are different types of DNA polymerases, each with specific roles in DNA replication and repair. In eukaryotic cells, DNA polymerase α, δ, and ε are involved in different stages of replication, while in prokaryotic cells, DNA polymerase III is the main enzyme for synthesizing new DNA.
In summary, DNA polymerase is the key enzyme that reads the original DNA strand and builds a new, complementary strand using the base-pairing rules. This process ensures that genetic information is faithfully transmitted from one generation of cells to the next.