ENADE: Medicina Veterinária · Brazil · INEP
Original practice questions written to the published syllabus · not past papersBiomolecules, enzymes and the metabolic pathways that turn feed into energy, milk, meat and eggs, including the ruminant's special dependence on volatile fatty acids and gluconeogenesis.
In the exams: ICAR AICE-JRF core group 08; ICAR AIEEA-PG 12 (Veterinary Biochemistry); China basic paper 12
How our questions for ENADE spread across the units of Veterinary Biochemistry. Difficulty: 36 easy, 31 medium, 0 hard.
| Biochemical laboratory techniques | 12 | |
| Minerals: biochemical roles | 8 | |
| Enzymes and enzyme kinetics | 7 | |
| Ruminant metabolism: volatile fatty acids, gluconeogenesis and ketogenesis | 6 | |
| Protein and amino-acid metabolism | 5 | |
| Nucleic acids | 5 | |
| Vitamins: biochemical roles | 5 | |
| Biomolecules and their interactions | 4 | |
| Carbohydrate metabolism | 4 | |
| Lipid metabolism | 4 | |
| Hormones | 4 | |
| Cell signalling | 3 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Lactose, the sugar of milk, is made of which two monosaccharides?
B. Galactose and glucose
Lactose is galactose beta-1,4 glucose. Glucose plus fructose is sucrose, and two glucose units form maltose.
Further reading: Nelson DL, Cox MM, Lehninger Principles of Biochemistry, 8th ed.
In a Lineweaver-Burk plot, lines for an enzyme with and without a competitive inhibitor:
D. intersect on the y-axis
Competitive inhibitors leave Vmax (and so 1/Vmax, the y-intercept) unchanged while increasing the slope. Intersection on the x-axis is the pure non-competitive pattern; parallel lines indicate uncompetitive inhibition.
Further reading: Nelson DL, Cox MM, Lehninger Principles of Biochemistry, 8th ed.
Which enzyme is the main rate-controlling step of glycolysis?
C. Phosphofructokinase-1
PFK-1 catalyses an irreversible step and is allosterically activated by AMP and fructose-2,6-bisphosphate and inhibited by ATP and citrate. Aldolase, isomerase and enolase catalyse near-equilibrium steps.
Further reading: Nelson DL, Cox MM, Lehninger Principles of Biochemistry, 8th ed.
Birds excrete most of their waste nitrogen as:
D. uric acid
Birds are uricotelic: they lack a functional hepatic urea cycle and make uric acid via purine synthesis, which is why arginine is essential in their diet. Mammals are ureotelic; many aquatic animals are ammonotelic.
Further reading: Nelson DL, Cox MM, Lehninger Principles of Biochemistry, 8th ed.
Which enzyme converts hypoxanthine and xanthine to uric acid?
B. Xanthine oxidase
Xanthine oxidase, a molybdenum enzyme inhibited by allopurinol, makes uric acid. Uricase oxidises uric acid to allantoin; HGPRT salvages purine bases.
Further reading: Nelson DL, Cox MM, Lehninger Principles of Biochemistry, 8th ed.
Thiamine pyrophosphate is the coenzyme of which enzyme?
A. Transketolase
TPP serves transketolase, pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. ALT uses pyridoxal phosphate, acetyl-CoA carboxylase uses biotin, and the mutase uses vitamin B12.
Further reading: Nelson DL, Cox MM, Lehninger Principles of Biochemistry, 8th ed.
Which of the following is a direct metabolic effect of insulin?
C. Inhibition of lipolysis
Insulin is the hormone of the fed state: it inhibits lipolysis, gluconeogenesis and ketogenesis and promotes glycogen synthesis. The other three are effects of glucagon and catecholamines.
Further reading: Nelson DL, Cox MM, Lehninger Principles of Biochemistry, 8th ed.
Why do ruminants develop fatty liver more readily than many simple-stomached species when NEFA flow to the liver is high?
C. Their liver exports triacylglycerol as VLDL slowly
Re-esterified triacylglycerol accumulates in hepatocytes when uptake exceeds export, and ruminant hepatic VLDL secretion is low. The liver esterifies readily; that is the source of the fat.
Further reading: Kaneko JJ, Harvey JW, Bruss ML (eds), Clinical Biochemistry of Domestic Animals, 6th ed.
Which tube is preferred when glucose measurement must be delayed?
A. Sodium fluoride-potassium oxalate
Fluoride inhibits enolase, stopping glycolysis by blood cells that would otherwise lower glucose. Unseparated plain or heparinised samples lose glucose with time; citrate is for coagulation tests.
Further reading: Stockham SL, Scott MA, Fundamentals of Veterinary Clinical Pathology, 2nd ed.
Blood urea nitrogen is reported as 28 mg/dL. What is the urea concentration in mmol/L (urea contains two nitrogen atoms; 28 g of N per mole of urea)?
D. 10 mmol/L
28 mg/dL = 280 mg N/L; each mmol of urea has 28 mg of N, so 280/28 = 10 mmol/L. Dividing by 60 (molar mass of urea) gives 4.7, a wrong basis because the value is urea nitrogen; 20 divides by 14, counting only one nitrogen; 1 forgets the dL-to-L factor.
Further reading: Nelson DL, Cox MM, Lehninger Principles of Biochemistry, 8th ed.
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