Be sure and have the data from the standard curve you constructed. Now, we will use that standard curve to determine the protein concentration of two solutions:

Unknown 1 and Unknown 2

Procedures
This part of the lab requires that you have constructed a standard curve and kept your data, if you haven't, go back and do so

Determine and record the absorbance and transmittance values at 560 nm, successively, for each of the different unknown solutions. Using the graph area below, plot the data with Protein concentration on the horizontal axis, absorbance on the left-hand vertical axis.

The unknown protein concentrations can be determined from the standard curve by drawing a horizontal line on the graph parallel to the X-axis and through the point on the Y-axis which corresponds to the absorbance. This line will intersect the standard curve; at this intersection, a vertical line is dropped to the X-axis and the concentration read from the X-axis.

Two factors are important in determining unknown or relative concentrations from a standard curve. The absorption value of the unknowns should be within your standard curve values (higher than the lowest & lower than the highest) .

Determine the absorbance of Unknown 1 (sample 1) and Unknown 2 (sample 2).

Be sure and have the data and standard curve you constructed on the previous page. Enter, then submit the Absorbance of your unknowns (samples 1 and 2). On the next page you will use your standard curve to determine the protein concentration of these two solutions:

Make sure you enter the absorbance values from the two samples above (not from someone else). The Absorbance @ 560 nm of the two unknowns you measured using the "virtual spec" above goes here. Sample 1 Absorbance was Sample 2 Absorbance was 1. What characteristic of a solution does a spectrophotometer measure? Light absorption Electrical absorption pH absorption Temperature absorption 2. Polymers of amino acids joined together are known as........? Proteins Lipids DNA RNA 3. In the Biuret test, there should be a linear relationship between absorbance and: Transmittance Wavelength Concentration Temperature 4. Why was a wavelength of 560nm chosen for the spectrophotometer in the biuret reaction experiment? Because it is the wavelength of maximum absorption Because it is the highest wavelength that can be achieved by a Spectronic 20 Because it is near the midpoint in the visible light range between 400nm and 700 Because it is in the UV light range 5. The graph below shows at standard curve constructed using Protein samples, Biuret test, and a Spec 20. What would the protein concentration of an unknown solution with an absorbance (560nm) of 0.5 be? ~ 50 mg/ml ~ 410 mg/ml ~ 500 mg/ml ~ 790 mg/ml Name: (*teaching moment) You know we can tell when you submit the form anonymously, check out the answers on the next page, and then submit them with your name. Instead of making you look clever or intelligent, its actually pretty lame. Not a good way to build a reputation as a good student (which can come in handy if you need letters of recommendation). Thanks Section: MAST Visitor Staff-001 Staff-002 Staff-003 Staff-004 Staff-005 Staff-006 Staff-007 Staff-008 Staff-009 Staff-010 Staff-011 Staff-012 Staff-013 Staff-014 Staff-501 Staff-502