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🥼organic chemistry review

DdCTP

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

ddCTP, or dideoxycytidine triphosphate, is a modified nucleotide used in the DNA sequencing method known as the Sanger sequencing technique. It plays a crucial role in determining the sequence of DNA molecules by acting as a chain terminator during DNA synthesis.

5 Must Know Facts For Your Next Test

  1. ddCTP is one of the four dideoxynucleotides (ddATP, ddGTP, ddCTP, and ddTTP) used in the Sanger sequencing method.
  2. The incorporation of ddCTP into a DNA strand during synthesis leads to the termination of DNA elongation, as it lacks the 3' hydroxyl group required for the formation of a phosphodiester bond.
  3. Sanger sequencing relies on the random incorporation of ddNTPs, including ddCTP, to generate a population of DNA fragments with varying lengths, which are then separated and analyzed to determine the sequence of the original DNA molecule.
  4. The presence of ddCTP in the sequencing reaction mixture, along with the four natural deoxynucleotides (dATP, dGTP, dCTP, and dTTP), allows for the selective termination of DNA synthesis at cytosine residues in the template DNA.
  5. The specific incorporation of ddCTP during DNA synthesis is detected and recorded, providing information about the sequence of the DNA molecule being analyzed.

Review Questions

  • Explain the role of ddCTP in the Sanger sequencing method.
    • In the Sanger sequencing method, ddCTP is a modified nucleotide that lacks a 3' hydroxyl group, which is necessary for the formation of a phosphodiester bond during DNA synthesis. When ddCTP is incorporated into a growing DNA strand, it terminates the elongation process, leading to the generation of DNA fragments of varying lengths. The random incorporation of ddCTP, along with the four natural deoxynucleotides, allows for the selective termination of DNA synthesis at cytosine residues, providing information about the sequence of the DNA molecule being analyzed.
  • Describe how the use of ddCTP in Sanger sequencing contributes to the determination of DNA sequences.
    • The incorporation of ddCTP in the Sanger sequencing reaction leads to the generation of a population of DNA fragments with varying lengths, each terminating at a cytosine residue. These fragments are then separated by size using gel electrophoresis, and the specific incorporation of ddCTP at each position is detected and recorded. By analyzing the pattern of these terminated fragments, the sequence of the original DNA molecule can be determined. The presence of ddCTP, along with the four natural deoxynucleotides, allows for the selective termination of DNA synthesis, enabling the reconstruction of the complete DNA sequence.
  • Evaluate the importance of ddCTP in the development and widespread adoption of the Sanger sequencing method for DNA sequencing.
    • The introduction of ddCTP, and the other dideoxynucleotides, was a crucial innovation that enabled the development of the Sanger sequencing method, which became the predominant DNA sequencing technique for several decades. The ability of ddCTP to terminate DNA synthesis, when randomly incorporated, allowed for the generation of a population of DNA fragments that could be analyzed to determine the sequence of a DNA molecule. This method was significantly more efficient and cost-effective compared to previous DNA sequencing approaches, contributing to its widespread adoption and the rapid advancement of genomic research. The availability of ddCTP, and its role in the Sanger sequencing process, was a fundamental aspect of the technological breakthroughs that transformed our understanding of genetics and the field of molecular biology.