| Criteria | Deoxynucleotides (dNTPs) | Dideoxynucleotides (ddNTPs) | Remarks |
| Definition | Natural building blocks of DNA consisting of a nitrogenous base, deoxyribose sugar, and one phosphate group. | Synthetic analogs of deoxynucleotides lacking the 3′-OH group on the sugar. | Both are used in DNA synthesis but differ in structure and function. |
| Sugar Component | Contains deoxyribose sugar with a hydrogen (-H) at the 2′ position and hydroxyl (-OH) at the 3′ position. | Contains deoxyribose sugar with hydrogen (-H) at both 2′ and 3′ positions (no 3′-OH). | The absence of 3′-OH in ddNTPs prevents chain elongation. |
| Role in DNA Synthesis | Serves as the normal substrate for DNA polymerases, allowing chain elongation. | Acts as a chain terminator during DNA synthesis when incorporated. | Structural difference is critical for controlled termination. |
| Occurrence | Naturally occurring in cells (dATP, dTTP, dCTP, dGTP). | Synthetic molecules used in laboratory techniques. | ddNTPs are not naturally found in cells. |
| Function in Experiments | Supports continuous DNA replication and amplification (e.g., PCR). | Used in Sanger sequencing to generate DNA fragments of defined length. | dNTPs are essential for life; ddNTPs are experimental tools. |
| Applications | DNA replication, PCR, qPCR, DNA repair studies. | DNA sequencing, mutation detection. | dNTPs provide continuity; ddNTPs provide termination for analysis. |
| Outcome when Incorporated | DNA chain continues to elongate. | DNA chain stops at the incorporation site. | The key feature enabling sequencing technology. |
