SPECTROPHOTOMETRY IN BIOTECHNOLOGY

SPECTROPHOTOMETRY IN BIOTECHNOLOGY

TOPICS • Spectrophotometers in Biotechnology • Light and its Interactions with Matter • Spectrophotometer Design • Spectrophotometer Operation • Qualitative Spectrophotometry • Quantitative Spectrophotometry • UV Spectrophotometry of DNA, RNA and Proteins • Calibration of Spectrophotometers

BIOTECHNOLOGY PROCESS Find gene that codes for useful protein Isolate gene Insert gene into vector Insert vector into cells (transform/transfect cells) Grow cells, cells manufacture protein product Purify product Sell product

BIOTECHNOLOGY PROCESS Find gene that codes for useful protein Estimate DNA [ ] Isolate gene Insert gene into vector Check cell density Insert vector into cells (transform/transfect cells) Grow cells, cells manufacture protein product Check protein activity Purify product Check protein concentration Sell product Check protein purity

Spectrophotometers in Biotechnology • Light and its Interactions with Matter • Spectrophotometer Design • Spectrophotometer Operation • Qualitative Spectrophotometry • Quantitative Spectrophotometry • UV Spectrophotometry of DNA, RNA and Proteins • Calibration of Spectrophotometers

LIGHT IS A TYPE OF ELECTROMAGNETIC RADIATION • Imagine electromagnetic radiation like waves on a pond • But instead of water, electromagnetic radiation is energy moving through space • Distance from one crest to the next is the wavelength

WAVELENGTH AND COLOR • Different wavelengths of light correspond to different colors • All colors blended together is called white light • The absence of all light is black • Light of slightly shorter wavelengths is ultraviolet • Eyes do not perceive UV light

WAVELENGTH OF VISIBLE LIGHT AND COLOR

INTERACTION OF LIGHT WITH MATERIALS IN SOLUTION • When light shines on a solution, it may pass through – be transmitted – or • Some or all of the light energy may be absorbed

THE ABSORPTION OF LIGHT AND COLOR OF SOLUTIONS

BIOLOGICAL SOLUTIONS • Usually appear clear to our eyes – have no color • DNA, RNA, most proteins do not absorb any visible light • But they do absorb UV light, so UV spectrophotometers are useful to biologists • Example, can use a detector that measures absorbance at 280 nm, or 254 nm to detect proteins

SPECTROPHOTOMETERS • Are instruments that measure the interaction of light with materials in solution

Monochromator Separates Light into Its Component Wavelengths. Modern Specs Use Diffraction Gratings

THE BLANK • Spectrophotometers compare the light transmitted through a sample to the light transmitted through a blank. • The blank is treated just like the sample • The blank contains everything except the analyte (the material of interest) • Contains solvent • Contains whatever reagents are added to the sample

WHEN OPERATING SPEC • Blank is inserted into the spectrophotometer • Instrument is set to 100% transmittance or zero absorbance

PROPER SELECTION, USE, AND CARE OF CUVETTES • Cuvettes are made from plastic, glass, or quartz. • Use quartz cuvettes for UV work. • Glass, plastic or quartz are acceptable visible work. • There are inexpensive plastic cuvettes that may be suitable for some UV work.

2. Cuvettes are expensive and fragile (except for “disposable” plastic ones). Use them properly and carefully. a. Do not scratch cuvettes; do not store them in wire racks or clean with brushes or abrasives. b. Do not allow samples to sit in a cuvette for a long period of time. c. Wash cuvettes immediately after use.

3. Disposable cuvettes are often recommended for colorimetric protein assays, since dyes used for proteins tend to stain cuvettes and are difficult to remove. 4. Matched cuvettes are manufactured to absorb light identically so that one of the pair can be used for the sample and the other for the blank.

5. Do not touch the base of a cuvette or the sides through which light is directed. 6. Make sure the cuvette is properly aligned in the spectrophotometer. 7. Be certain to only use clean cuvettes.

EXAMPLES • Some examples of qualitative spectrophotometry • The absorbance spectra of various common solvents. Note that some solvents absorb light at the same wavelengths as DNA, RNA, and proteins • Hemoglobin bound to oxygen versus carbon monoxide • Native versus denatured bovine serum albumin (a protein commonly used in the lab)

OVERVIEW OF QUANTITIVE SPECTROPHOTOMETRY A. Measure the absorbance of standards containing known concentrations of the analyte B. Plot a standard curve with absorbance on the X axis and analyte concentration on the Y axis C. Measure the absorbance of the unknown(s) D. Determine the concentration of material of interest in the unknowns based on the standard curve

LINEAR RANGE • If there is too much or too little analyte, spectrophotometer cannot read the absorbance accurately

COLORIMETRIC ASSAYS • Quantitative assays of materials that do not intrinsically absorb visible light • Combine the sample with reagents that make the analyte colored • The amount of color is proportional to the amount of analyte present

BRADFORD PROTEIN ASSAY • A quantitative colorimetric assay • Used to determine the concentration, or amount, of protein in a sample

Prepare standards with known protein concentrations • Add Bradford Reagent to the samples and to standards • Read absorbances • Create a standard curve • Determine the concentration of protein in the samples based on the standard curve

MORE ABOUT THE CALIBRATION LINE ON A STANDARD CURVE • Three things determine the absorbance of a sample: • The concentration of analyte in the sample • The path length through the cuvette • The intrinsic ability of the analyte to absorb light at the wavelength of interest

BEER-LAMBERT LAW A =  B C Where: A = absorbance at a particular wavelength  = absorptivity constant – intrinsic ability of analyte to absorb light at a particular wavelength B = path length through cuvette C = concentration of analyte

APPLYING THE EQUATION • Suppose you have a sample: • And you know the path length • And you know the absorptivity constant for the analyte of interest at a particular wavelength • Then, measure the sample’s absorbance at the specified wavelength

Can calculate the concentration of the analyte from the Beer-Lambert equation A =  B C • But this is a shortcut that may give inaccurate results!

EQUATION FOR A LINE A =  B C y = m x + 0

Y intercept should be zero because of the blank • Blank has no analyte (zero concentration) and is used to set transmittance to 100% = absorbance to zero

SPECTROPHOTOMETRY IN BIOTECHNOLOGY