- #1
biologyquestions
- 1
- 0
why dna absorbs best at 260nm?
Exploring DNA Absorption at 260nm in Molecular Biology
- Thread starter biologyquestions
- Start date
In summary, molecular biology photometry is a technique that uses a spectrophotometer to measure the absorbance of light by molecules in a sample. This allows for the quantification of DNA, RNA, and proteins in molecular biology experiments. It is a fast, accurate, and non-destructive method with relatively low cost. However, it requires a pure sample and cannot detect molecules with low absorbance or distinguish between different types of molecules. It is also limited to measuring molecules with aromatic rings, such as DNA, RNA, and proteins.
- #2
berkeman
Mentor
- 68,287
- 21,982
Welcome to PF. 
What have you found so far in your searching? What do you find when you use that phrase in a Google search?biologyquestions said:
FAQ: Exploring DNA Absorption at 260nm in Molecular Biology
What is the significance of measuring DNA absorption at 260nm?
Measuring DNA absorption at 260nm is significant because DNA absorbs ultraviolet light most strongly at this wavelength. This absorption is primarily due to the presence of aromatic nucleotide bases. It is a common method used to quantify DNA concentration and to assess the purity of DNA samples in molecular biology.
How is the purity of DNA determined using the 260/280 ratio?
The purity of DNA is determined by measuring the absorbance at 260nm and 280nm and calculating the ratio (A260/A280). Pure DNA typically has a ratio of ~1.8. A lower ratio indicates protein contamination, while a higher ratio may suggest contamination with RNA or other substances.
What are the common contaminants that can affect DNA absorption measurements?
Common contaminants that can affect DNA absorption measurements include proteins, phenol, and other organic compounds. Proteins absorb strongly at 280nm, which can skew the A260/A280 ratio. Phenol and other organic contaminants can absorb at various wavelengths, affecting the accuracy of DNA quantification.
How can you prepare a DNA sample for accurate absorption measurement at 260nm?
To prepare a DNA sample for accurate absorption measurement at 260nm, ensure the DNA is dissolved in a suitable buffer, such as TE buffer (Tris-EDTA). Avoid using solutions that absorb UV light, like phenol or high concentrations of salts. Dilute the DNA sample appropriately to fall within the linear range of the spectrophotometer.
What are the limitations of using UV absorbance at 260nm for DNA quantification?
The limitations of using UV absorbance at 260nm for DNA quantification include the inability to distinguish between DNA and RNA, potential interference from contaminants, and the requirement for relatively pure samples. Additionally, absorbance measurements can be affected by the presence of nucleotides, single-stranded DNA, and other nucleic acids.