#DNA quantification

DNA & RNA isolation

Which of the following is used to quantify DNA using fluorescence?

Fluorescent quantification of DNA employs DNA-binding fluorochromes for sensitivity beyond UV absorbance. SYBR Green I is a cyanine dye that exhibits extremely low fluorescence when free but over 1000-fold enhancement upon intercalation into minor groove of double-stranded DNA. This allows specific quantitation of dsDNA even with contaminants present. Coomassie Blue stains proteins, DAPI binds AT-rich dsDNA but is used mainly for microscopy, and TRIS is a buffer. SYBR Green is standard for real-time PCR quantification and fluorometric assays with high specificity and linearity.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Electrophoresis

Densitometry is used to:

Densitometry involves scanning electrophoretic gels after staining with dyes like ethidium bromide or Coomassie blue. A densitometer measures absorbance or fluorescence intensity of each band. The peak area and height are directly proportional to concentration of macromolecule present. By comparing with known standards, absolute amount of DNA, RNA or protein can be estimated. It provides quantitative analysis beyond qualitative visualization, unlike simple band counting or purity assessment by spectrophotometry ratio. Thus quantification is its primary application in molecular biology laborato

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Electrophoresis

Which method provides more accurate DNA quantification on gels?

Accurate DNA quantification on gels requires measurement of fluorescence intensity proportional to DNA mass. Visual estimation by eye comparing to ladder is subjective and semiquantitative. Densitometry employs gel documentation systems with CCD cameras and software to integrate band pixel intensity, generating quantitative curves calibrated against standards. This provides objective measurement of amount and molecular weight. Tracking dye comparison monitors migration, not mass. Heat mapping is not standard. Therefore densitometric analysis offers superior precision and reproducibility for DN

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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PCR Modifications

Which molecule does not distinguish between different DNA sequences in qPCR?

SYBR Green is an asymmetrical cyanine dye that intercalates into the minor groove of any double-stranded DNA without sequence recognition. Fluorescence increases over thousand-fold upon binding, providing signal proportional to total double-stranded product accumulation. In contrast, TaqMan, molecular beacons and Scorpion probes rely on complementary hybridization of oligonucleotide sequences containing fluorophore and quencher, thus discriminating specific amplicons from nonspecific products. Melting curve analysis is required with SYBR Green to verify product identity, as primer-dimers and o

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details