Biology · MU Pleven

17.Denaturation, renaturation and hybridization of DNA. Hibridization of NA in Southern and Northern blotting and PCR.

Covers DNA denaturation, with causes such as heat, extreme pH and chemical denaturants, and the melting temperature, then renaturation and the factors that affect its rate. Moves on to hybridization and the probe types used, then Southern and Northern blotting step by step with their applications, and the annealing step in PCR with primer design details. Closes with stringency conditions, probe types and the significance of hybridization.

Inside: 10 sections · 5 labelled pictures · 33 flashcards · 5 min

Topic 17 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 10 sections, about 616 words (5 min of reading), with 33 flashcards.

In this note

  1. Denaturation, renaturation and hybridization of DNA. Hibridization of NA in Southern and Northern blotting and PCR.
  2. DENATURATION OF DNA
  3. RENATURATION (REANNEALING) OF DNA
  4. HYBRIDIZATION OF NUCLEIC ACIDS
  5. SOUTHERN BLOTTING – DNA–DNA HYBRIDIZATION
  6. NORTHERN BLOTTING – RNA–DNA HYBRIDIZATION
  7. HYBRIDIZATION IN PCR (ANNEALING STEP)
  8. STRINGENCY CONDITIONS
  9. TYPES OF PROBES USED IN HYBRIDIZATION
  10. SIGNIFICANCE OF DNA HYBRIDIZATION

DENATURATION OF DNA

  • Denaturation refers to the separation of the two strands of the DNA double helix.
  • Occurs due to the breaking of hydrogen bonds between base pairs; phosphodiester bonds remain intact.
  • Major causes:
  • Heat (increased temperature leads to strand separation).
  • Extreme pH (alkaline solutions disrupt hydrogen bonding).
  • Chemical denaturants (e.g., urea, formamide).
  • Denatured DNA shows hyperchromic effect → increased absorbance at 260 nm due to unstacking of bases.
  • Melting temperature (Tm):
  • Temperature at which 50% of DNA becomes single‑stranded.
  • Higher in GC‑rich DNA due to 3 hydrogen bonds in G–C pairs.
  • Increases with higher ionic strength (salt stabilizes negative phosphate backbone).
  • Denaturation is reversible under controlled conditions.

RENATURATION (REANNEALING) OF DNA

  • Process where two complementary single‑stranded DNA molecules reassociate to form a stable double helix.
  • Conditions required:
  • Temperature ~20–25°C below Tm to allow stable base pairing.
  • Adequate salt concentration (Na⁺ ions shield negative charges on DNA).
  • Sufficient time for strands to find complementary sequences.
  • Factors influencing renaturation rate:
  • Sequence complexity → simpler, repetitive sequences reanneal faster.
  • DNA concentration → higher concentrations increase chances of complementary strand encounters.
  • Fragment length → shorter fragments anneal more quickly.
  • Basis for Cot curves, used to study genome size and complexity.

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