39 clinical MCQs in Biochemistry. In purine biosynthesis carbon atoms at the 4 and 5 positions and N at 7 position are deriv. Kenya, Africa and global r...
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Q1. In purine biosynthesis carbon atoms at the 4 and 5 positions and N at 7 position are derived from ---
- Glycine
- Glutamine
- Alanine
- Threonine
- $\text{HCO}_3^-$
Answer: Glycine
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Q2. The key molecule in the biosynthesis of purine nucleotides is phosphribosyl pyrophosphate. This molecule is formed from ---
- $\alpha$-D-ribose 5-phosphate
- 5-phospho $\beta$-D-ribosylamine
- D-RIBOSE
- Deoxyribose
- ATP
Answer: $\alpha$-D-ribose 5-phosphate
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Q3. Gout is a metabolic disorder of catabolism of ---
- Pyrimidine
- Purine
- Alanine
- Phenylalanine
- Cysteine
Answer: Pyrimidine
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Q4. Lesch-Nyhan syndrome, the sex linked recessive isorder is due to the lack of the enzyme. ---
- Xanthine oxidase
- Adenine phoshoribosyl transferase
- Adenosine deaminase
- Hypoxanthine-guanine phosphoribosyl transferse
- Guanase
Answer: Xanthine oxidase
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Q5. In the biosynthesis of purine nucleotides the AMP feedback regulates ---
- Adenylosuccinase
- Adenylosuccinate synthetase
- IMP dehygdronase
- HGPR Tase
- DHO dehydrogenase
Answer: Adenylosuccinase
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Q6. All the following amino acids can enter the TCA cycle as $\alpha$-ketoglutarate EXCEPT ---
- Glutamine
- Histidine
- Arginine
- Methionine
- Proline
Answer: Glutamine
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Q7. Lysine is degraded into ---
- Pyruvate
- AcetylCoA
- AcetoacetylCoA
- SuccinylCoA
- $\alpha$-ketoglutarate
Answer: Pyruvate
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Q8. Which of the following amino acid is considered both ketogenic and glucogenic ---
- Valine
- Tryptophan
- Lysine
- Histidine
- Proline
Answer: Valine
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Q9. Homocystinuria leads to elevated levels of ---
- Cysteine
- Methionine
- Cystathionine
- α-ketoglutrate
- Serine
Answer: Cysteine
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Q10. Maple syrup urine disease is caused by ---
- Fumaryl acetoacetate deficiency
- Branched chain α-keto acid dehydrogenase deficiency
- Branched chain α-keto acid dehydrogenase upregulation
- Decarboxylase deficiency
- Malonyl-CoA mutase deficiency
Answer: Fumaryl acetoacetate deficiency
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Q11. Organisms that excrete amino nitrogen as ammonia are ---
- Ammylopteric
- Uricoteric
- Ammonoteric
- Uritotelic
- Amminoteric
Answer: Ammylopteric
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Q12. Three of the four urea cycle enzymatic reactions takes place in the ---
- Mitochondria
- Cytosol
- Endoplasmic reticulum
- Golgi apparatus
- Lysosome
Answer: Mitochondria
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Q13. Dysfunction of urea cycle can result in ---
- Hyperammoneamia
- Hyperglyceamia
- Protienuria
- Hypoammonemia
- Acute pancreatitis
Answer: Hyperammoneamia
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Q14. The following two amino acids are exclusively ketogenic ---
- Tyrosine and phenylalanine
- Methionine and cysteine
- Aspartate and Glutamate
- Leucine and Lysine
- Glycine and valine
Answer: Tyrosine and phenylalanine
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Q15. The following two compounds can be used by the brain for energy production ---
- Fumarate and oxaloacetate
- Acetone and β-hydroxybutyrate
- Pyruvate and phosphoenol pyruvate
- citrate and malate
- Glyceraldehyde-3-phosphate and Dihydroxyacetone phosphate
Answer: Fumarate and oxaloacetate
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Q16. Hypocalcaemia results from ---
- Too much sun
- Too much estrogen secretion
- Parathyroid hyperactivity
- Lack of vitamin D
- Lack of Vitamin $\text{B}_6$
Answer: Too much sun
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Q17. When an enzyme catalyzes a reaction ---
- Substrates bind in the active sites
- Products bind in the active sites
- The shape of the enzyme remains unchanged
- The enzyme is consumed by the reaction
- None of the above.
Answer: Substrates bind in the active sites
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Q18. Pellagra is caused by the deficiency of which vitamin? ---
- Ascorbic acid
- Pyridoxine
- Niacin
- Thymine
- Vitamin K
Answer: Ascorbic acid
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Q19. The key regulatory enzyme of cholesterol synthesis is ---
- HMGCoA synthase
- HMGCoA lyase
- HMGCoA kinase
- HMGCoA synthetase
- HMGCoA reductase
Answer: HMGCoA synthase
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Q20. McArdle's disease is characterised by the deficiency of ---
- Muscle glycogen phosphorylase
- Liver glycogen phosphorylase
- Glucose 6-phosphatase
- Phosphofructokinase
- $\alpha$-1-6 Glucosidase
Answer: Muscle glycogen phosphorylase
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Q21. A lysosomal storage disease manifested in childhood that is as a result of deficiency of sphingomyelinase is ---
- Tay Sach's
- Gaucher's
- Niemann-Pick's
- Fabry's
- Gangliosidosis
Answer: Tay Sach's
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Q22. Out of the 24 ATPs formed in the TCA cycle, 2 ATPs are formed at substrate-level by the following reaction ---
- Citrate-Isocitrate
- $\text{Isocitrate} - \alpha\text{-ketoglutarate}$
- SuccinylCoA-Succinate
- Succinate – fumarate
- Malate – oxaloacetate
Answer: Citrate-Isocitrate
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Q23. One of the following is referred to as "bad cholesterol" ---
- Chylomicrons
- VLDL
- LDL
- HDL
- Cholesteryl ester
Answer: Chylomicrons
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Q24. How many malonyl groups are consumed in the cytoplasmic synthesis of palmitate? ---
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Q25. The most predominant component of chylomicrons is ---
- Phosphoglycerides
- Triacylglycerols
- Cholesterol
- Sphingolipids
- Glycolipids
Answer: Phosphoglycerides
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Q26. The major storage form of lipids in mammalian tissues is ---
- Cholesterol esters
- Phospholipids
- Free fatty acids
- Sphingolipids
- Triacylglycerols
Answer: Cholesterol esters
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Q27. The following are true regarding the pKa values of Aspartic acid indicated as 2.0, 3.9 and 10.0, EXCEPT ---
- The isoelectric pH is the arithmetic mean of the three pKa values
- The isoelectric pH is 3.0
- Aspartic acid can be separated from the amino acid mixture at the isoelectric pH
- The net charge of aspartic acid at isoelectric pH is zero.
- The solubility will be decreased at the isoelectric Branched chain α-ketoacid dehydrogenase deficiency
Answer: The isoelectric pH is the arithmetic mean of the three pKa values
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Q28. The solubility of alcohols in water ---
- Decreases with an increase in molecular mass
- Is greater than that of the carboxylic acid of equal molecular mass
- Increases as the carbon chain length increases
- Is a result of hydrogen bonding between the alcohol and the water molecules
- decreases with increasing number of OH groups
Answer: Decreases with an increase in molecular mass
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Q29. The following are intermolecular forces operating in biological molecules, EXCEPT ---
- Hydrogen bonds
- Dipole-dipole interactions
- Covalent bonds
- Hydrophobic forces
- Van-der-waal forces
Answer: Hydrogen bonds
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Q30. Buffer solutions ---
- will always have a pH of 7.0
- Are rarely found in living systems
- Cause a decrease in pH when acids are added
- causes an increase in pH when bases are added
- Tend to maintain a relatively constant pH on addition of acids and bases
Answer: will always have a pH of 7.0
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Q31. Tri-acylgycerols ---
- Are soluble in water
- Maintain the structure of cell membranes
- Are stored in the adipocytes cells of the adipose tissue
- Can easily form micelles in water
- Are hydrophobic products of mono- and diacylglycerols.
Answer: Are soluble in water
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Q32. The phenomenon where the solubility of a protein is lowered at high salt concentration is known as ---
- Electrophoresis
- Salting-in process
- Isoelectric focusing
- Salting-out process
- Bioelectric pH
Answer: Electrophoresis
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Q33. In an RNA-DNA hybrid duplex, respectively ---
- U base pairs with T
- U base pairs with A
- T base pairs with A
- G base pairs with A
- C base pairs with A
Answer: U base pairs with T
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Q34. Which of the following would interfere with the ability of an enzyme to catalyze a reaction? ---
- Reduced concentration of the substrate available
- Reduced concentration of the product available
- Increases concentration of the substrate available
- A change in pH
- None of the above
Answer: Reduced concentration of the substrate available
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Q35. The following is true with regards to translation process ---
- Initiator amino acyl-tRNA $f^{met}$ only enters through P-Site of a ribosome
- Initiator amino acyl-tRNA $f^{met}$ only enters through A-Site of a ribosome
- Initiator amino acyl-tRNA $f^{met}$ enters through P or A -Site of a ribosome
- Initiator amino acyl-tRNA $f^{met}$ is the activated amino acid in eurkaryotes
- All the above statements are false
Answer: Initiator amino acyl-tRNA $f^{met}$ only enters through P-Site of a ribosome
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Q36. During protein biosynthesis(translation) ---
- 5' end sequence of mRNA correspond to C terminus of a polypeptide
- 5' end sequence of mRNA correspond to N terminus of a polypeptide
- 3' end sequence of mRNA correspond to N terminus of a polypeptide
- 3' end sequence of mRNA correspond to either C or N terminus of a polypeptide
- 5' end sequence of mRNA correspond to either C or N terminus of a polypeptide
Answer: 5' end sequence of mRNA correspond to C terminus of a polypeptide
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Q37. Chloramphenicol ---
- Inhibits DNA replication
- Causes misreading of the mRNA code
- Blocks the translocation step of protein synthesis
- Inhibits the activity of eEF-2 by ADP-ribosylation
- Inhibits peptidyl transferase in prokaryotes
Answer: Inhibits DNA replication
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Q38. The following is NOT a direct inhibitor of protein biosynthesis ---
- Tunicamycin
- Neomycin
- Streptomycin
- Tetracyclines
- Rifampicin
Answer: Tunicamycin
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Q39. The following is NOT a post-translational modification of protein in eurkaryotes
- Phosphrylation
- Glycosylation
- Removal of signal peptide
- Peptide bond formation
- Formation of S-S (disulfide) linkages. --- Source: biochemistry/questions/bchem EOY 2013.pdf.
Answer: Phosphrylation