Biochemical Engineering
Core concepts
Biochemical engineering applies transport and reaction principles to biological systems. Know enzyme kinetics: Michaelis–Menten rate, Km and Vmax, Lineweaver–Burk linearisation, and inhibition types (competitive, non-competitive, uncompetitive). For cell growth, understand Monod kinetics, specific growth rate, yield coefficients, maintenance energy, and product formation (growth-associated vs non-growth-associated). Master bioreactor types (stirred tank, airlift, packed bed, membrane) and modes (batch, fed-batch, continuous/chemostat). Aeration and oxygen transfer are critical: kLa, oxygen uptake rate, and the balance between supply and demand. Sterilisation, downstream processing (centrifugation, filtration, chromatography) and immobilisation are tested. Also cover biosafety and GMP concepts.
Traps
Do not confuse Km (substrate affinity; lower means higher affinity) with Vmax. In competitive inhibition, Km rises but Vmax is unchanged; non-competitive lowers Vmax. Chemostat steady state: dilution rate D = μ, and washout occurs when D exceeds μmax. Oxygen is often the limiting nutrient in aerobic fermentation - check kLa before assuming substrate limitation.
Worked rule of thumb
Michaelis–Menten: v = Vmax·S/(Km + S). When S = Km, v = Vmax/2. In a chemostat, biomass concentration X = Yx/s·(S0 − S) and substrate follows Monod; washout when D > μmax. A quick check: if measured v is half of Vmax, substrate equals Km.
Exam strategy
Identify the rate-limiting step (kinetics, oxygen transfer, or mixing) and write the balance for the bioreactor mode before substituting numbers.