Phosphodiester Bond
Definition
The covalent linkage between consecutive nucleotides in a strand, formed between the phosphate group and the 3'-OH of the preceding sugar and the 5'-carbon of the next sugar. Hydrolysis of phosphodiester bonds by nuclease enzymes or by chemical attack (acid, heat) is the primary cause of DNA strand breakage in degraded evidence.
- Location
- Between consecutive nucleotides within a strand
- Chemistry
- Links phosphate to 3'-OH and 5'-carbon of adjacent sugars
- Breakage cause
- Nuclease hydrolysis, acid, or heat
- Forensic effect
- Primary cause of DNA strand breakage in degraded evidence
Common questions
How does phosphodiester bond breakage affect STR profiling of old evidence?+
As bonds break, the DNA fragments into shorter pieces, so larger STR loci fail to amplify first while smaller loci still succeed, producing the characteristic partial or degraded profile seen in old or environmentally exposed samples.
Why does heat accelerate phosphodiester bond breakage?+
Elevated temperature increases the rate of hydrolysis reactions generally, so warm or fluctuating storage conditions speed up random backbone cleavage compared with cool, stable storage, which is why evidence is kept refrigerated or frozen.
Do nucleases target phosphodiester bonds specifically or DNA generally?+
Nucleases are enzymes specialised to cleave phosphodiester bonds, and environmental or bacterial nucleases present at a scene are a major driver of DNA degradation before evidence is even collected and stabilised.
Related terms
- Antiparallel Orientation
- The two strands of the DNA double helix run in opposite directions: one strand reads 5' to 3', its complement reads 3'...
- Base Pair (Bp)
- A complementary pairing of nitrogenous bases on opposite strands of double-stranded DNA: adenine with thymine (two hydrogen bonds) or guanine with cytosine...
- Complementarity
- The property by which each base pairs with only one specific partner (A with T, G with C). Complementarity allows a single...
- Denaturation
- The separation of double-stranded DNA into two single strands by disrupting the hydrogen bonds between base pairs. In PCR, denaturation is achieved...
- Nucleotide
- The monomer unit of nucleic acids. Each nucleotide consists of a five-carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group,...