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DNA and RNA Extraction from Blood, Tissue, and Saliva: Essential Protocols for Genomic Research

Introduction: 

Why DNA and RNA Extraction Matters in Genomics

High-quality DNA and RNA extraction is the first and most critical step in any molecular biology or Next-Generation Sequencing (NGS) workflow. Whether you’re analyzing human genetics, detecting mutations, or conducting infectious disease surveillance, the integrity of your nucleic acids directly impacts your results.

This guide outlines standardized, efficient methods for extracting DNA and RNA from blood, tissue, and saliva  three of the most commonly used biological materials in genomics labs.

DNA Extraction :  Principles and Applications

DNA (deoxyribonucleic acid) is the genetic blueprint of all living organisms. Extracting clean, intact DNA is essential for:

  • Whole genome sequencing (WGS)

  • PCR and qPCR
  • Genotyping
  • Epigenetic studies

Let’s look at the best protocols based on sample type:

1.1 DNA Extraction from Blood (EDTA tubes)

Materials Needed:

  • EDTA-collected blood
  • Lysis buffer (RBC lysis solution)
  • Proteinase K
  • SDS (Sodium dodecyl sulfate)
  • Phenol-chloroform (or a commercial spin column kit)
  • Ethanol or isopropanol
  • TE buffer

Protocol :

  1. Lysis of red blood cells with RBC lysis buffer
  2. Pellet white blood cells (WBCs) by centrifugation
  3. Resuspend WBCs in nucleic lysis buffer
  4. Add Proteinase K and SDS, incubate to digest proteins
  5. Extract DNA using phenol-chloroform or spin column
  6. Precipitate DNA with cold ethanol or isopropanol
  7. Wash pellet with 70% ethanol
  8. Dissolve DNA in TE buffer and store at -20°C

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1.2 DNA Extraction from Tissue (fresh/frozen)

Materials Needed:

  • Fresh or frozen tissue (~25 mg)
  • Lysis buffer with SDS
  • Proteinase K
  • RNase A (to remove RNA)
  • Phenol-chloroform or kit
  • Ethanol or isopropanol

Protocol Overview:

  1. Homogenize tissue with pestle or bead mill
  2. Add lysis buffer + Proteinase K → incubate at 56°C overnight
  3. Add RNase A to remove RNA
  4. Proceed with DNA extraction using phenol-chloroform or commercial kits
  5. Precipitate and wash DNA
  6. Resuspend in TE buffer or water


1.3 DNA Extraction from Saliva (non-invasive sampling)

Materials Needed:

  • Saliva collection tubes (Oragene, Genotek)
  • Lysis buffer
  • Proteinase K
  • Isopropanol
  • Ethanol
  • TE buffer

Protocol Overview:

  1. Mix saliva with lysis buffer and incubate
  2. Add Proteinase K, incubate at 56°C
  3. Precipitate DNA with isopropanol
  4. Wash with 70% ethanol
  5. Resuspend DNA in TE buffer

Advantages of saliva sampling:

  • Non-invasive
  • Stable at room temperature
  • Suitable for population-scale studies

2.RNA Extraction From Cells to Transcriptomes

RNA (ribonucleic acid) provides insight into gene expression, mRNA splicing, and viral genomes. High-quality RNA extraction is vital for:

  • RNA-Seq
  • RT-PCR
  • Transcriptomic profiling
  • Pathogen detection

RNA is more delicate than DNA, so RNase-free conditions and quick processing are important.

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2.1 RNA Extraction from Blood

Materials Needed:

  • PAXgene blood RNA tubes or fresh EDTA blood
  • TRIzol or other RNA lysis reagent
  • Chloroform
  • Isopropanol
  • 75% ethanol
  • RNase-free water

Protocol Overview:

  1. Add TRIzol to blood sample
  2. Mix and incubate
  3. Add chloroform, centrifuge to separate phases
  4. Collect upper aqueous phase
  5. Precipitate RNA with isopropanol
  6. Wash pellet with 75% ethanol
  7. Air-dry and dissolve in RNase-free water


2.2 RNA Extraction from Tissue

Materials Needed:

  • Fresh/frozen tissue (~30 mg)
  • Liquid nitrogen
  • TRIzol
  • Chloroform
  • Isopropanol
  • Ethanol
  • RNase-free water

Protocol Overview:

  1. Snap-freeze and grind tissue in liquid nitrogen
  2. Add TRIzol, homogenize
  3. Proceed as with blood protocol (phase separation, precipitation, wash)
  4. Treat with DNase if needed
  5. Quantify RNA with Nanodrop or Bioanalyzer

2.3 RNA Extraction from Saliva

Note: RNA yield from saliva is lower and often used for viral RNA or microbiome studies.

Materials:

  • Saliva + stabilizing solution (or direct use)
  • RNA lysis buffer (TRIzol or commercial kit)
  • Chloroform
  • Isopropanol
  • DNase I
  • RNase-free water

Protocol :

Same as above, with particular attention to RNase control and fast processing.

Best Practices for DNA/RNA Extraction

  • Use gloves and RNase-free consumables
  • Verify purity using A260/A280 and A260/A230 ratios
  • Store DNA at -20°C and RNA at -80°C
  • Avoid repeated freeze-thaw cycles
  • Use DNase for RNA samples and RNase for DNA samples when purity is critical

Conclusion:

 High-Quality Nucleic Acids = High-Quality Data

Whether you're working on clinical diagnostics, research genomics, or NGS workflows, extracting pure and intact DNA and RNA is non-negotiable. BGI provides trusted genomic services, but the success starts at the bench  with sample quality.

If you're looking for sequencing services, library prep, or custom bioinformatics, BGI is ready to support your project.

 Contact us or explore our full services at

 bgi-international.com.