6. Lab Calculations, Standards, DNA Note & Data Interpretation

Which equation is appropriate for a simple dilution from a stock solution?

C1V1 = C2V2

Explanation:1. A — The dilution equation conserves solute amount when preparing a diluted solution.

You need 200 mL of 50 mM Tris from a 1.0 M stock. What stock volume is required?

10 mL

Explanation:2. C — V1 = C2V2/C1 = (0.050 M × 200 mL)/1.0 M = 10 mL.

A 1:2 dilution means:

One volume sample plus one volume diluent, giving twice the original volume

Explanation: The SDS-PAGE protocol mixes 10 µL sample with 10 µL of 2× Laemmli buffer to make a 1:2 dilution.

If 10 µL of sample is mixed with 10 µL of 2× sample buffer, what is the final sample-buffer strength?

1×

Explanation: Equal-volume mixing halves the 2× buffer concentration to 1×.

How many microliters are in 1 mL?

1000

Explanation: 1 mL = 1000 µL.

A 0.5% (w/v) solution contains:

0.5 g solute per 100 mL solution

Explanation: Percent weight/volume is grams per 100 mL.

How much solute is needed to make 20 mL of a 0.5% (w/v) solution?

0.1 g

Explanation: 0.5 g/100 mL × 20 mL = 0.10 g.

Why must standards be included when estimating molecular weight by gel filtration?

They create a calibration relationship between Ka and log(MW)

Explanation: Known standards anchor the calibration curve used to estimate an unknown.

Why is a standard curve useful in quantitative assays?

It maps instrument response to known analyte amounts/concentrations

Explanation: Unknown signals can be interpolated from the response of known standards.

If an unknown's signal lies outside the standard-curve range, the best next step is generally:

Dilute or otherwise adjust the sample to bring its signal into the calibrated range

Explanation: Interpolation within the validated range is more reliable than extrapolation.

What does a blank correct for in a spectrophotometric measurement?

Background absorbance from solvent/buffer/reagents and cuvette

Explanation: The blank establishes the baseline for the sample matrix.

Which graph type is appropriate for plotting Michaelis–Menten rate against substrate concentration?

Scatter plot

Explanation:12. A — A scatter plot shows the relationship between continuous substrate concentration and measured rate.

Which Excel plot is used for the double-reciprocal analysis?

Scatter plot of 1/v0 versus 1/[S]

Explanation: Lineweaver–Burk analysis uses reciprocal substrate and velocity values.

Why should units be carried through every calculation?

To detect dimensional errors and ensure the final quantity has the correct units

Explanation: Unit tracking is a key check on calculations such as concentration, rate, and turnover number.

A rate is measured as 0.30 absorbance units/min. What additional information is needed to convert it to concentration/time?

Extinction coefficient and path length

Explanation: Beer–Lambert law gives Δc/Δt = (ΔA/Δt)/(εl).

If the total assay volume is 6.0 mL, why must it be used in concentration calculations?

Final concentrations depend on the total reaction volume

Explanation: The manual explicitly reminds students that assay calculations must reflect the 6 mL total volume.

What is the appropriate interpretation of an R² value near 1 for a calibration line?

The fitted line explains a large fraction of the variation in the calibration data

Explanation: A high R² indicates a strong linear fit for the plotted calibration data, though it does not alone prove accuracy.

The accompanying DNA/kinetics PDF contains which substantive instruction relevant to this lab series?

Use Bradford concentration and SDS-PAGE molecular weight to calculate lactase kcat

Explanation: The readable page in that PDF is a note connecting Bradford protein concentration and SDS-PAGE molecular weight to kcat; no DNA protocol is readable there.

Which statement about the provided materials is most accurate?

The chromatography manual details gel filtration; Lab 94–123 details SDS-PAGE and lactase kinetics; the short DNA/kinetics note links Bradford and SDS-PAGE to kcat

Explanation: This describes the scope of the supplied readable material without adding procedures that are not present.

When writing a lab report, which practice best supports reproducibility?

Record exact sample/lane identities, standards, conditions, units, and analysis steps

Explanation: The manual specifically asks students to record lane contents and standards; complete methods and data records support reproducibility.