23-Chem-B4 Biochemical Engineering · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exam 04-Chem-B4, Biochemical Engineering — May 2013. 3 hours, Closed-Book Exam (any non-communicating calculator permitted). Six questions are printed; any five (5) constitute a complete paper (100 marks) and only the first five as they appear in the answer book are marked. All six are solved below for completeness.
Reference texts: Shuler & Kargi, Bioprocess Engineering: Basic Concepts, 2nd ed.; Bailey & Ollis, Biochemical Engineering Fundamentals, 2nd ed.; Madigan et al., Brock Biology of Microorganisms, 13th ed.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
| Compound | Structure | Biological function |
|---|---|---|
| Protein | Linear polymer of amino acids joined by peptide bonds (primary structure); folds into α-helices/β-sheets (secondary) stabilised by backbone H-bonds, then into a compact 3-D shape (tertiary) via hydrophobic packing, ionic and disulfide bonds; multiple subunits may assemble (quaternary). | Enzymes (catalysis, incl. all the Monod-kinetics enzymes above), structural support (collagen, cytoskeleton), transport (haemoglobin), immune defence (antibodies), signalling (hormones, receptors), motor function. |
| DNA | Double helix of two antiparallel deoxyribonucleotide strands (deoxyribose–phosphate backbone); complementary bases pair by H-bonding, A=T (2 bonds) and G≡C (3 bonds). | Stores the cell's genetic information; template for semi-conservative replication (cell division) and for transcription into RNA (gene expression). |
| RNA | Single-stranded polynucleotide (ribose–phosphate backbone; bases A, U, G, C), can fold back on itself via internal base-pairing. | mRNA carries the genetic code from DNA to the ribosome; tRNA delivers the matching amino acid via anticodon–codon pairing; rRNA is the structural/catalytic core of the ribosome itself. |
| ATP | Adenine base + ribose sugar + a chain of three phosphate groups linked by two high-energy phosphoanhydride bonds. | The cell's universal energy currency: hydrolysis of the terminal phosphate (ATP→ADP+Pi, ΔG≈−30.5 kJ/mol) drives otherwise-endergonic reactions — biosynthesis, active transport, mechanical work, and phosphorylation-based signalling. |
| Phospholipids | Amphipathic molecule: a hydrophilic phosphate-containing head group attached (via a glycerol backbone) to two hydrophobic fatty-acid tails. | Self-assemble spontaneously into a bilayer in water, forming the structural basis of every cell membrane — a selective permeability barrier that houses the embedded transport and signalling proteins. |
Bacteria are classified by where they get their carbon (heterotrophic = organic; autotrophic = CO2) and where they get their electrons/energy (organic compounds, or an inorganic/light source), independently of whether the terminal electron acceptor is O2 (aerobic) or something else (anaerobic).
| Bacteria type | Carbon source | Electron donor | Electron acceptor | Main metabolic products |
|---|---|---|---|---|
| (1) Aerobic heterotrophic (e.g. Pseudomonas, most activated-sludge bacteria) |
Organic compounds (e.g. glucose, other biodegradable organics) | Organic compounds (same substrate) | O2 | CO2 + H2O + new biomass |
| (2) Aerobic autotrophic (e.g. Nitrosomonas/Nitrobacter – chemolithoautotrophs) |
CO2 (fixed via the Calvin cycle) | Inorganic compounds (e.g. NH4+, NO2−, H2S, Fe2+) | O2 | Oxidised inorganic by-product (e.g. NO2−/NO3−, SO42−, Fe3+) + fixed biomass |
| (3) Anaerobic heterotrophic (e.g. Clostridium – fermenters; sulfate-reducers – anaerobic respirers) |
Organic compounds | Organic compounds (same substrate) | No O2: either an internal organic intermediate (fermentation, e.g. pyruvate) or an external inorganic acceptor such as NO3−, SO42− or CO2 (anaerobic respiration) | Reduced end-products — lactate, ethanol + CO2, or (via anaerobic respiration) N2, H2S, CH4 — + biomass |
