Three fitted curves, one uninhibited, one competitive and one uncompetitive, let this SC335 Unit 5 enzyme kinetics worksheet name each inhibition by the constants that changed, inhibition constants included. Searches like "sc 335 unit 5 assignment example", "sc335 unit 5 sample" and "sc335 unit 5 example" land here.
What a finished SC335 Unit 5 enzyme kinetics worksheet looks like
Four pages: a data table, two figures, a results table, four short answers and a script appendix. The data table gives rates at 0.10 to 3.20 mM substrate for each series, in micromolar per minute. Figure one plots rate against substrate for all three series on ordinary axes, with the fitted curves drawn through the points; figure two shows the double-reciprocal plot for display, the uncompetitive lines running parallel and the competitive line meeting the uninhibited one at the vertical axis. The results table reports the fitted constants: Km 0.40 mM and Vmax 1.20 without inhibitor, Km 1.26 and Vmax 1.23 with 2.0 mM phosphate, Km 0.134 and Vmax 0.400 with 5.0 mM phenylalanine. Answers name each inhibition type and compute Ki near 0.92 mM for phosphate and about 2.5 mM for phenylalanine.
How a SC335 Unit 5 example is structured
Fitting comes before interpreting, and the worksheet explains why the fit uses the untransformed rates: reciprocals stretch the error at low substrate, and a double-reciprocal line through these same data gives a Km of 0.384 instead of 0.397. That plot is kept, labeled as a picture of the fitted result rather than the method. Each inhibition is named from evidence in a fixed order, what happened to Vmax, then Km, then the ratio between them, so the name follows from the numbers. Phosphate leaves Vmax within noise of the uninhibited value while roughly tripling Km, the signature of competition for the active site, which fits phosphate being the reaction's own product. Phenylalanine divides both constants by the same factor, about three, leaving their ratio unchanged, the pattern of an inhibitor that binds only the enzyme-substrate complex. Inhibition constants follow from each factor.
Fitted on ordinary axes
Nonlinear fitting to the untransformed rates gives the reported constants, and the worksheet shows the small distortion the reciprocal method would have introduced on the same data.
A double-reciprocal plot kept for display
Parallel and intersecting lines make the inhibition patterns easy to see, so the plot stays as a figure while the numbers come from the direct fit.
Vmax first, then Km
Each inhibitor is classified by checking the maximum rate before the Michaelis constant, which keeps the name tied to evidence instead of to a remembered picture.
Product as competitor
Phosphate released by the enzyme occupies the same site as the substrate's phosphate group, which the worksheet uses to make chemical sense of the competitive pattern.
Both constants divided by three
L-phenylalanine lowers Km and Vmax by the same factor, and the worksheet points to the unchanged ratio as the identifying feature of uncompetitive inhibition.
Where marks go in SC335 Unit 5
An inhibition type named from the look of a double-reciprocal plot, with no constants reported, earns little, since the question at stake is what changed and by how much. Confusing uncompetitive with noncompetitive inhibition is the error graders flag most often on this worksheet; one lowers Km and Vmax together, the other lowers Vmax while leaving Km alone. Constants read from reciprocal plots of noisy data, reported to more digits than the fit supports, overstate precision. Missing units on Km or rate cost points each time they occur. A Ki computed with the wrong factor, or without the inhibitor concentration, loses calculation credit even when the type is right. Scripts or spreadsheets without comments, figures lacking legends, and axis labels that omit units account for smaller deductions.
Get a SC335 Unit 5 example written to your instructions
Upload your SC335 Unit 5 data sheet or simulation output with the rubric, noting whether a script, a spreadsheet or graph-paper plots is expected. The free first custom worksheet, done within 24-48h, fits your data by the method your section names and reports every constant with its units and the evidence behind each inhibition call.
SC335 Unit 5 questions, answered
Why not just use a Lineweaver-Burk plot?
It is useful for seeing inhibition patterns, but taking reciprocals magnifies the error in the slowest, least precise rates, which then pull the fitted line. Fitting the Michaelis-Menten equation directly to the rates avoids that. Many sections still ask for the double-reciprocal plot, so include it if required, but report constants from a direct fit when your tools allow.
How do I tell uncompetitive from noncompetitive inhibition?
Compare what happened to both constants. Noncompetitive inhibition lowers Vmax and leaves Km unchanged, because the inhibitor binds enzyme and enzyme-substrate complex equally. Uncompetitive inhibition lowers both Km and Vmax by the same factor, because the inhibitor binds only the enzyme-substrate complex. On a double-reciprocal plot, noncompetitive lines meet on the horizontal axis and uncompetitive lines run parallel.
What if my data do not fit any pattern cleanly?
Report what the fit shows and say so. Real data often sit between patterns, and mixed inhibition, where both constants change by different factors, is a legitimate result. State the fitted constants with their uncertainty, name the closest pattern, and explain the discrepancy, such as noise at low substrate concentrations, rather than forcing the data into a textbook category.