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Integrated Workflows & Reference

Advanced IBO practical biochemistry molecular-biology
Preparing for: IBO Guide General Guide
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Integrated Workflows - What You Will Actually Face

IBO practicals rarely test a single technique in isolation. Instead, they build integrated workflows where each step feeds into the next. Here are the four major patterns:

Workflow A - “Purify, then Quantify, then Assay” (IBO 2018, 2023)

  1. Ni-NTA chromatography to purify the His-tagged protein from bacterial lysate.
  2. Bradford assay on the elution fractions to determine protein concentration.
  3. Activity assay (gel retardation in 2018; colorimetric diaphorase assay in 2023) on the fraction with the highest protein concentration.
  4. Calculate specific activity (U mg$^{-1}$) = total activity / total protein.

This is the most common workflow pattern. It tests your ability to connect purification to quantification to functional assay.

Workflow B - “Genotype, then Phenotype, then Pathway” (IBO 2015)

  1. Restriction mapping or PCR genotyping to identify which gene is mutated.
  2. Auxotrophy plate test to determine which supplement restores growth.
  3. Map the blocked enzymatic step by combining genotype and phenotype data.

This workflow tests the connection between molecular biology (DNA analysis) and classical genetics (growth phenotypes).

Workflow C - “Clinical Case, then Enzyme Kinetics, then Inheritance” (IBO 2017)

  1. Haematological indices (MCV, MCH, MCHC, reticulocyte count) to characterise the anaemia.
  2. Pyruvate kinase kinetic parameters ($K_M$, $V_{\max}$) to quantify enzyme deficiency.
  3. Pedigree analysis with genetic markers to determine inheritance pattern.

This workflow is the most integrative - it connects clinical medicine, enzymology, and genetics in a single exam.

Workflow D - “Modifier Effects on the Active Site” (IBO 2022)

  1. Measure baseline ADH activity.
  2. Pre-incubate the enzyme with a modifier (EDTA or PCMB).
  3. Re-assay activity and calculate the percentage change.
  4. Deduce which amino acid residues and/or cofactors are essential for catalysis.

This workflow tests your ability to interpret inhibition data in terms of protein structure and mechanism.

Walk through each workflow step by step – click through to see data flow between techniques:

Mathematical Toolkit

These are the formulas you need to have memorised cold. They come up in almost every practical exam.

QuantityFormulaUnits
Enzyme activity$\dfrac{\Delta A \times V_{\text{total}}}{\varepsilon \times V_{\text{enzyme}} \times \Delta t}$U mL-1
Specific activityActivity / [protein]U mg-1
$K_M$[S] at $V_{\max}/2$, or from Hanes-Woolf x-interceptmM or uM
$k_{\text{cat}}$$V_{\max} / [\text{E}]$s-1
MCV$\dfrac{\text{Hct (\%)} \times 10}{\text{RBC } (\times 10^{12} \text{ L}^{-1})}$fL
MCH$\dfrac{\text{Hb (g dL}^{-1}\text{)} \times 10}{\text{RBC}}$pg
MCHC$\dfrac{\text{Hb}}{\text{Hct}} \times 100$g dL-1
Generation time$g = t / n$, where $n = \log_2(N_t / N_0)$hours or minutes
SC50Interpolated from SC% vs log[concentration] plotmg mL-1

Universal Exam Traps (Across All Years)

These are the mistakes that cost students marks every single year. Read them carefully.

  1. Resin or column runs dry - irreversible damage, no replacement.
  2. Wrong dilution factor when calculating the original concentration from a diluted sample.
  3. Delta-t in seconds instead of minutes - this gives an activity value 60-fold too high.
  4. Bubbles in cuvettes or 96-well plates - scatter light, inflate absorbance.
  5. Light exposure during Bradford or other photosensitive assays.
  6. Mis-assignment of DNA topology on agarose gels - supercoiled, open-circular, and linear DNA all migrate differently even at the same molecular weight.
  7. Forgetting controls - no-enzyme blanks, no-substrate blanks, uncut-DNA controls, no-template PCR controls.
  8. Writing decimal commas instead of points on computer-read answer sheets (IBO uses Anglo conventions).
  9. Estimating kinetic parameters from non-linear regions of the progress curve or the Michaelis-Menten plot.
  10. Starting short tasks first and running out of time for long incubations - always start the longest incubation first.

Year-Specific Reference Index

Each year’s practical has its own character. Use this table to jump to the techniques you need to practise.

YearHostFocusKey techniques
2015Aarhus, DenmarkMolecular biologyRestriction mapping, PCR genotyping, yeast auxotrophy
2016Hanoi, VietnamBiochemistry + microbiologyIPTG induction, Ni-NTA, SDS-PAGE, gel filtration, DPPH antioxidant, lactic acid fermentation
2017Warwick, UKClinical biochemistryHaematological indices, PK coupled assay, Michaelis-Menten kinetics, pedigree
2018Tehran, IranProtein-DNA interactionsNi-NTA, Bradford, gel retardation (EMSA), DNase protection, restriction theory
2022Yerevan, ArmeniaEnzymologyADH spectrophotometric assay, EDTA/PCMB modifier effects, active-site deductions
2023UAE UniversityIntegrated biochemistryNi-NTA, Bradford, diaphorase colorimetric assay, Michaelis-Menten, kcat, expression hosts

Self-Assessment Questions

Test yourself on these questions. Model answers are provided - try to answer each one before reading the answer.

1. Why must the Ni-NTA resin never be allowed to run dry?

Model answer Drying collapses the resin matrix and irreversibly damages the nickel-binding sites. The column loses all binding capacity and cannot be recovered.

2. A student obtains A595 = 0.35 for a 1.5-fold diluted eluate. From the standard curve, this corresponds to 0.22 mg/mL. What is the original concentration?

Model answer 0.22 x 1.5 = 0.33 mg/mL. Forgetting the dilution factor is the most common Bradford assay mistake.

3. Calculate the ADH activity if delta-A = 0.45 over 1.5 min, V1 = 3.0 mL, V2 = 0.1 mL.

Model answer

$$\frac{0.45 \times 3.0}{6.22 \times 0.1 \times 1.5} \approx 1.45 \text{ U mL}^{-1}$$

4. Why does EDTA inhibit yeast ADH more strongly than PCMB?

Model answer EDTA removes the essential catalytic Zn2+ completely, collapsing the active-site structure. PCMB modifies only a subset of the cysteine residues (or does so incompletely under the assay conditions), so residual activity remains.

5. Why is LDH added in large excess in the PK coupled assay?

Model answer To ensure the LDH step is never rate-limiting. The observed rate must reflect only PK activity, so the coupling enzyme must convert pyruvate to lactate as fast as it is produced.

6. Calculate MCV for a patient with Hct = 36%, RBC count = 4.0 x 10^12 /L.

Model answer MCV = (36 x 10) / 4.0 = 90 fL. This is within the normal range (normocytic).

7. Why do mature red blood cells depend so heavily on PK activity?

Model answer Mature RBCs lack mitochondria and cannot perform oxidative phosphorylation. Glycolysis is their sole ATP source, and PK catalyses the final ATP-generating step.

8. A yeast mutant grows on minimal + Tyr + Phe but not on minimal + Trp. Which gene is most likely mutated?

Model answer ARO7, the branch-point enzyme after chorismate that leads to the Tyr/Phe branch. The Trp branch (via TRP5) is unaffected, which is why Trp supplementation does not help.

9. What would you expect on the gel if Pep protein completely protects plasmid DNA from DNase?

Model answer The Pep + DNase lane shows the same retarded bands as the Pep-only lane, while the DNase-only lane shows a degradation smear or loss of bands. Protection = preservation of intact DNA-protein complex.

10. Why is the same wavelength (595 nm) used for both the Bradford assay and the diaphorase/NBT assay?

Model answer Coincidence. The Coomassie-protein complex and the reduced NBT formazan both happen to absorb maximally at 595 nm. They are chemically unrelated.
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These integrated workflows all lean on the same idea: a colour change read at a fixed wavelength stands in for a concentration. BiOLab’s protocol archive lets you run that kind of colorimetric assay yourself and log a real result, not just interpolate a given standard curve.

Final Study Strategy

  1. Master the foundation layer first - pipetting, Beer-Lambert, time management. These are not glamorous, but they are the difference between clean data and noise.
  2. Learn one technique per day from the bottom up: first principles, then protocol, then traps.
  3. Practise the integrated workflows under timed conditions. Set a 90-minute timer and work through a complete past practical from start to finish.
  4. Do the self-assessment questions - all of them, not just the easy ones.
  5. Re-draw every standard curve and Michaelis-Menten plot from memory. If you can sketch the expected shape and label the axes correctly, you understand the technique.
  6. Teach the technique to a peer. If you can explain the “why” behind each step, you own it.

Static Reference Images

Images to be added: flowchart of the four integrated workflows (A through D), IBO practical lab bench photograph.