Second or third year undergraduate

Biochemistry practical

Buffers, protein quantitation, and enzyme kinetics: the calculations a biochemistry practical repeats every week, with the temperature correction that catches most pH mistakes.

12 calculators, in the order the course uses them. Every one shows its working, flags the hazards, and keeps working offline once the page has loaded. Free, and no account is needed.

Start with Buffer / pH All topics and reference tables

In course order

What this practical calculates

1. Buffer / pH

Henderson-Hasselbalch, the acid/base split for a target pH.

How it works · Practice problems · pH = pKa + log₁₀([A⁻]/[HA])

2. Buffer pH temperature corrector

Dial in the bench pH so your buffer hits target at working temperature.

How it works · Practice problems · pH_bench = pH_target − (dpKa/dT)·(T_work − T_prep)

3. Molarity, mass and volume conversion

Convert between molarity, mass, volume, and moles for a reagent, in any direction.

How it works · Practice problems · n = m / MW ; c = n / V

4. Simple dilution

C₁V₁ = C₂V₂, exactly how much stock and diluent to mix.

How it works · Practice problems · C₁ · V₁ = C₂ · V₂

5. Protein by A280

Protein concentration from absorbance and extinction coefficient.

How it works · Practice problems · c (mg/mL) = A280 / (E0.1% x path)

6. Bradford / BCA protein assay

Fit a standard curve, subtract the blank, and back-calculate protein with dilution.

How it works · C = (A − blank − intercept) / slope

7. Protein extinction coefficient (A280)

Sequence to ε280, MW, and E0.1%, the Pace way. Feeds the A280 calculator.

How it works · ε280 = nW·5500 + nY·1490 + nSS·125

8. Beer-Lambert (absorbance to concentration)

Concentration from absorbance, any extinction-coefficient convention.

How it works · Practice problems · A = ε · c · l

9. SDS-PAGE gel

Resolving & stacking gel recipes by acrylamide %.

How it works · Practice problems · recipe by %T

10. Enzyme activity

Total units and specific activity from a measured rate.

How it works · Practice problems · specific activity = U / mg

11. Michaelis-Menten (Vmax, Km)

Fit enzyme kinetics to read Vmax, Km, and (with [E]t) kcat and kcat/Km.

How it works · v = Vmax · [S] / (Km + [S])

12. Standard curve

Fit a linear or quadratic standard curve (Bradford, BCA, ELISA) and read unknowns.

How it works · signal = slope x conc + intercept

Worth telling students once

The mistakes this practical produces every year

Tris shifts about -0.028 pH units per degree C. A buffer titrated at the bench is a different pH in the cold room, and the temperature corrector shows by how much.

A protein with no tryptophan or tyrosine barely absorbs at 280 nm, so an A280 reading on one is not a concentration measurement.

For the person running the course

If you want this page named for your course

What it costs

Nothing, for you and for your students, permanently. There is no licence to sign, no account for students to create, no data to hand over, and nothing for your IT department to approve or install.

What you would get

A page named for your course, with your calculations in your order and your conventions, at a stable URL you can paste into your course management system once and reuse every year.

What we would like back

To be told when it is wrong. If a value, a convention, or a hazard note does not match how your course teaches it, that is a bug worth fixing.

Ask for a page for your course

The honest caveat

Aliquot is an educational aid, not a safety authority and not a certified instrument. Students should verify critical values and follow the safety data sheet and your institution's protocols.

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