ICAR AICE-JRF/SRF (PhD) — Food Processing Technology, Food Safety & Quality, Processing and Food Engineering · India · ICAR through the National Testing Agency
Original practice questions written to the published syllabus · not past papersThe structure of biomolecules and the metabolic pathways that turn food into energy and body tissue. Food chemistry (phase 2) describes how these molecules behave in a food; this subject explains how they behave in the body and in living raw materials such as respiring fruit and post-mortem muscle.
In the exams: ICAR AIEEA-PG Code 18 Unit I (metabolism of carbohydrates, lipids and protein; BV and PER)
How our questions for ICAR AICE-JRF/SRF spread across the units of General Biochemistry & Metabolism. Difficulty: 0 easy, 5 medium, 11 hard.
| Biochemistry of post-harvest respiration and post-mortem muscle | 3 | |
| Enzymes: classification, mechanism, Michaelis-Menten kinetics and inhibition | 2 | |
| Bioenergetics, ATP and the electron transport chain | 2 | |
| Nucleic acids, replication, transcription and translation | 2 | |
| Biochemical laboratory techniques: centrifugation, electrophoresis and spectrophotometry | 2 | |
| Coenzymes and vitamins as cofactors | 1 | |
| Carbohydrate metabolism: glycolysis, TCA cycle, gluconeogenesis and glycogen | 1 | |
| Lipid metabolism: beta-oxidation and fatty-acid synthesis | 1 | |
| Protein and amino-acid metabolism and the urea cycle | 1 | |
| Hormonal regulation of metabolism | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
An allosteric enzyme gives a sigmoidal plot of rate against substrate concentration. What does this shape indicate?
A. Cooperative binding between subunits
Sigmoidal kinetics arise when binding at one site changes the affinity of others, as in multi-subunit regulatory enzymes; the Michaelis-Menten equation, which gives a hyperbola, does not apply. Irreversible inhibition lowers activity overall; a log scale makes even a hyperbola look sigmoidal, but the question concerns a plot against concentration.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
An assay containing 1.0 µM enzyme reaches Vmax = 600 µM of product per minute. What is kcat?
A. 10 s⁻¹
kcat = Vmax/[E]total = 600 µM min⁻¹/1.0 µM = 600 min⁻¹ = 10 s⁻¹. 600 s⁻¹ forgets to convert minutes to seconds; 36 000 s⁻¹ multiplies by 60 instead of dividing; 0.1 s⁻¹ inverts the ratio.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
2,4-Dinitrophenol increases oxygen consumption by mitochondria while ATP synthesis falls. Why?
C. It carries protons across the membrane, collapsing the gradient
As an uncoupler, dinitrophenol shuttles protons back into the matrix, so electron transport runs fast with nothing to slow it, but no gradient remains to drive ATP synthase; the energy becomes heat. Blocking complex I would reduce oxygen uptake; oligomycin, not dinitrophenol, inhibits ATP synthase.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
What is the main methodological advance of DIAAS over PDCAAS in protein-quality scoring?
D. It uses ileal digestibility of each amino acid, without truncation
The digestible indispensable amino acid score, recommended by FAO in 2013, corrects each indispensable amino acid for its own ileal digestibility, avoiding the overestimation that faecal digestibility gives, and reports values above 100% without truncation. PDCAAS uses faecal protein digestibility and is capped at 1.0; rat growth is the basis of PER.
Further reading: Lehninger Principles of Biochemistry; FAO Food and Nutrition Paper 92 (2013)
In PCR, what happens during the annealing step?
B. Primers bind to complementary sequences on single-stranded templates
Annealing, at a temperature set by the primers, lets them hybridise to the template. Separation is denaturation; extension is the polymerase step; gel visualisation is after PCR.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
In the lac operon of Escherichia coli, what happens when lactose is present and glucose is absent?
D. The repressor is released and transcription of the lac genes is high
Allolactose binds the repressor and removes it from the operator; with glucose absent, cAMP-CRP activates the promoter, so expression is high. Catabolite repression operates when glucose is present; bacterial genes are not spliced.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
Which technique combines separation by isoelectric point with separation by molecular mass?
D. Two-dimensional gel electrophoresis
2D electrophoresis runs isoelectric focusing in the first dimension and SDS-PAGE in the second, resolving hundreds of proteins. Native agarose separates by size and charge of DNA or proteins; gel filtration by size; a Western blot detects specific proteins with antibodies after electrophoresis.
Further reading: Wilson and Walker, Principles and Techniques of Biochemistry and Molecular Biology
Ten here, 16 in the app. The Laisha app has every practice question we have written to ICAR AICE-JRF/SRF in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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