GATE — Life Sciences (XL), Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
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 GATE spread across the units of General Biochemistry & Metabolism. Difficulty: 10 easy, 23 medium, 3 hard.
| Nucleic acids, replication, transcription and translation | 8 | |
| Enzymes: classification, mechanism, Michaelis-Menten kinetics and inhibition | 6 | |
| Biochemical laboratory techniques: centrifugation, electrophoresis and spectrophotometry | 6 | |
| Bioenergetics, ATP and the electron transport chain | 5 | |
| Carbohydrate metabolism: glycolysis, TCA cycle, gluconeogenesis and glycogen | 4 | |
| Biomolecules: carbohydrates, amino acids, proteins, lipids and nucleic acids | 3 | |
| Lipid metabolism: beta-oxidation and fatty-acid synthesis | 3 | |
| Protein and amino-acid metabolism and the urea cycle | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Which level of protein structure is held mainly by hydrogen bonds between backbone C=O and N–H groups?
B. Secondary structure
α-Helices and β-sheets are stabilised by hydrogen bonds between backbone carbonyl and amide groups. Primary structure is the covalent sequence; quaternary structure is the association of subunits through side-chain interactions.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
A competitive inhibitor is added to an enzyme assay. What happens to the apparent Km and Vmax?
B. Km increases; Vmax is unchanged
A competitive inhibitor competes for the active site; enough substrate can outcompete it, so Vmax is reached but more substrate is needed (higher apparent Km). Unchanged Km with lower Vmax is pure non-competitive inhibition; both falling is uncompetitive.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
Using modern P/O ratios, how many ATP are formed when one NADH from the mitochondrial matrix is oxidised by the electron transport chain?
C. About 2.5
About 10 protons are pumped per NADH and about 4 are needed per ATP (including transport), giving about 2.5 ATP. 1.5 is the value for FADH₂; 3 is the older integral value.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
According to the chemiosmotic theory, what directly drives ATP synthesis in mitochondria?
A. The flow of protons back through ATP synthase
Electron transport pumps protons out; their return through the F₀F₁ ATP synthase drives its rotation and ATP formation. Electrons never reach ADP, GTP is a substrate-level product, and oxygen is reduced at complex IV.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
What is the net yield of glycolysis per molecule of glucose?
D. 2 ATP and 2 NADH
Four ATP are made, but two are invested, leaving net 2 ATP, plus 2 NADH from glyceraldehyde 3-phosphate dehydrogenase. 4 ATP is the gross figure; 36 ATP is an older figure for complete aerobic oxidation.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
How many NADH, FADH₂ and GTP are produced per acetyl-CoA oxidised in the TCA cycle?
B. 3 NADH, 1 FADH₂, 1 GTP
Isocitrate, α-ketoglutarate and malate dehydrogenases give 3 NADH; succinate dehydrogenase gives 1 FADH₂; succinyl-CoA synthetase gives 1 GTP (or ATP). The other combinations do not match the cycle's dehydrogenases.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
In the urea cycle, where do the two nitrogen atoms of urea come from?
D. One from free ammonia and one from aspartate
Carbamoyl phosphate brings one nitrogen from NH₃ (via carbamoyl phosphate synthetase I) and argininosuccinate synthetase adds the second from aspartate. Ornithine is the carrier and is regenerated, so it contributes no nitrogen to urea.
Further reading: Lehninger Principles of Biochemistry; FAO Food and Nutrition Paper 92 (2013)
A double-stranded DNA contains 20% adenine. What percentage is guanine?
C. 30%
By Chargaff's rules, A = T = 20%, so A + T = 40% and G + C = 60%, giving G = 30%. 20% assumes all bases are equal; 40% gives G = A + T; 60% gives G + C together.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
Which DNA sample has the highest melting temperature?
D. One with 70% G + C
G-C pairs have three hydrogen bonds and stronger stacking than A-T pairs, so DNA richer in G + C needs more heat to separate its strands. 70% A + T is the same as 30% G + C.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
Which statement about eukaryotic messenger RNA processing is correct?
A. It is capped, polyadenylated and spliced to remove introns
The primary transcript is capped, polyadenylated and spliced (introns out, exons joined) in the nucleus before export. Bacteria generally lack introns and translate mRNA as it is being transcribed.
Further reading: Lehninger Principles of Biochemistry; Berg et al., Biochemistry
Ten here, 36 in the app. The Laisha app has every practice question we have written to GATE 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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