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  Section: Biotechnology Methods » Molecular Biology
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Estimation of DNA purity and Quantification

Molecular Biology
  The Central Dogma
  Protein Synthesis in Cell Free Systems
  Polytene Chromosomes of Dipterans
  Salivary Gland Preparation (Squash Technique)
  Extraction of Chromatin
  Chromatin Electrophoresis
  Extraction and Electrophoresis of Histones
  Karyotype Analysis
  In Situ Hybridization
  Culturing Peripheral Blood Lymphocytes
  Microslide Preparation of Metaphases for In-Situ Hybridization
  Staining Chromosomes (G-Banding)
  Nucleic Acids
  Extraction of DNA from Bovine Spleen
  Purification of DNA
  Characterization of DNA
  DNA-Dische Diphenylamine Determination
  Melting Point Determination
  CsCl-Density Separation of DNA
  Phenol Extraction of rRNA (Rat liver)
  Spectrophotometric Analysis of rRNA
  Determination of Amount of RNA by the Orcinol Method
  Sucrose Density Fractionation
  Nucleotide Composition of RNA
  Isolation of Genomic DNA—DNA Extraction Procedure
  Isolation of Genomic DNA from Bacterial Cells
  Preparation of Genomic DNA from Bacteria
  Extraction of Genomic DNA from Plant Source
  Extraction of DNA from Goat Liver
  Isolation of Cotton Genomic DNA from Leaf Tissue
  Arabidopsis Thaliana DNA Isolation
  Plant DNA Extraction
  Phenol/Chloroform Extraction of DNA
  Ethanol Precipitation of DNA
  Isolation of Mitochondrial DNA
  Isolation of Chloroplast DNA
  DNA Extraction of Rhizobium (CsCl Method)
  Isolation of Plasmids
  RNA Isolation
  Preparation of Vanadyl-Ribonucleoside Complexes that Inhibit Ribonuclease Activity
  RNA Extraction Method for Cotton
  Isolation of RNA from Bacteroids
  Isolation of RNA from Free-Living Rhizobia
  Estimation of DNA purity and Quantification
  Fungal DNA Isolation
  Methylene Blue DNA Staining
  Blotting Techniques—Southern, Northern, Western Blotting
  Preparing the Probe
  Southern Blotting (First Method)
  Southern Blotting (Second Method)
  Western Blotting
  Western Blot Analysis of Epitoped-tagged Proteins using the Chemifluorescent Detection Method for Alkaline Phosphatase-conjugated Antibodies
  Southern Blot
  Southern Analysis of Mouse Toe/Tail DNA
  Northern Blotting
  Restriction Digestion Methods—Restriction Enzyme Digests
  Restriction Digestion of Plasmid, Cosmid, and Phage DNAs
  Manual Method of Restriction Digestion of Human DNA
  Preparation of High-Molecular-Weight Human DNA Restriction Fragments in Agarose Plugs
  Restriction Enzyme Digestion of DNA
  Electroelution of DNA Fragments from Agarose into Dialysis Tubing
  Isolation of Restriction Fragments from Agarose Gels by Collection onto DEAE Cellulose
  Ligation of Insert DNA to Vector DNA
  PCR Methods (Polymerase Chain Reaction)
  Polymerase Chain Reaction
  DNA Amplification by the PCR Method

Characterization by spectrophotometric method.


The DNA isolated from living cells is usually contaminated with protein, RNA, and salts used during the isolation process. The purity of DNA may be estimated by utilizing the property of the heterocyclic rings of the nucleotides of absorbing light strongly in the UV range. DNA absorbs maximum light energy at about 260 nm. An optical density of 1.0 corresponds to approximately 50 µg/mL of double stranded DNA. The ratio of absorbance viz. A260/A2SO and A2SO/ A260 provides an estimation regarding the purity of DNA. A typically pure preparation of good-quality DNA should exhibit the following spectral properties:
    - A260/A2SO ≈ 1.80
    - A2SO/A260 ≈ 0.55

  • Sample DNA
  • TE buffer:Tris-HCI, 10 mM EDTA, 1 mM; pH 8.0
  • Spectrophotometer and quartz cuvette


To find out the purity of DNA, make the appropriate dilution with TE buffer, and measure the absorbance at 260 nm and 280 nm.  

Do not use glass or plastic cuvettes, as lights in the UV range do not pass through these.

  1. Calculate A260/A280 and A280/A260, and check if the values are within the acceptable limit.
  2. Calculate the Dt~A concentration as follows:
    Concentration of DNA = (A260 × 50 × dilution factor) in mg/mL.


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