In a dideoxy DNA sequencing experiment, four separate reactions are carried out to provide the replicated material for DNA sequencing gels. Reaction products are usually run in gel lanes labeled A, T, C, and G.

Identify the nucleotides used in the dideoxy DNA sequencing reaction that produces molecules for the A lane of the sequencing gel.

Key Concepts

Dideoxy Nucleotide Triphosphates (ddNTPs)

Dideoxy nucleotide triphosphates (ddNTPs) are modified nucleotides used in DNA sequencing. Unlike regular deoxynucleotides, ddNTPs lack a hydroxyl group at the 3' carbon, preventing further elongation of the DNA strand once incorporated. This property allows for the termination of DNA synthesis at specific bases, which is crucial for determining the sequence of nucleotides in the DNA template.

Chain Termination Method

The chain termination method is a technique used in dideoxy DNA sequencing where DNA polymerase synthesizes new DNA strands. In this method, the incorporation of a ddNTP leads to the termination of the growing DNA strand, resulting in fragments of varying lengths. Each reaction contains a specific ddNTP (A, T, C, or G), allowing for the identification of the corresponding base in the original DNA sequence based on the length of the fragments produced.

Gel Electrophoresis

Gel electrophoresis is a laboratory technique used to separate DNA fragments based on their size. In the context of dideoxy sequencing, the reaction products are loaded into a gel, and an electric current is applied, causing the negatively charged DNA fragments to migrate towards the positive electrode. The resulting pattern of bands corresponds to the different lengths of DNA fragments, which can be analyzed to determine the sequence of nucleotides in the original DNA sample.