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Test Bank - Lehninger Principles of
Biochemistry, 7th Edition (Nelson, 2018)
Chapter 1-28 | All Chapters
1. Which of the following is the main driving force for protein folding in an
aqueous environment? A. Ionic interactions B. Hydrogen bonds C. Van der Waals interactions
D. Hydrophobic effect
The hydrophobic effect drives nonpolar side chains into the interior of proteins, minimizing contact with water and stabilizing the folded structure.
2. What is the primary structure of a protein?
A. The overall 3D shape
B. The sequence of amino acids
C. Alpha-helices and beta-sheets D. Multiple polypeptide chains interacting The primary structure is the linear sequence of amino acids in a polypeptide chain.
3. In Michaelis-Menten kinetics, what does Km represent?
A. Maximum velocity
B. Catalytic efficiency
C. Substrate concentration at half-maximal velocity
D. Turnover number Km reflects the substrate concentration at which the reaction rate is half of Vmax, indicating enzyme affinity for substrate.
4. Which amino acid contains a thiol group?
A. Alanine
B. Cysteine
C. Serine D. Lysine Cysteine has a thiol (-SH) group, which can form disulfide bonds important for protein structure.
5. Which of the following is a purine?
A. Cytosine B. Thymine
C. Guanine
D. Uracil Purines have a two-ring structure; guanine and adenine are purines.
6. What stabilizes the double helix of DNA?
A. Covalent bonds between bases B. Phosphodiester bonds between base pairs
C. Hydrogen bonding and base stacking interactions
D. Glycosidic linkages
10. What is the role of NAD+ in metabolism?
A. Enzyme activator
B. Electron carrier
C. Proton pump D. Structural protein NAD+ accepts electrons during redox reactions, becoming NADH, and serves as an electron carrier.
11. Which complex of the electron transport chain does not pump protons?
A. Complex I B. Complex III
C. Complex II
D. Complex IV Complex II (succinate dehydrogenase) transfers electrons but does not contribute to the proton gradient.
12. The enzyme responsible for carbon fixation in the Calvin cycle is:
A. PEP carboxylase
B. Rubisco
C. Malate dehydrogenase D. Pyruvate carboxylase Rubisco catalyzes the fixation of CO₂ to ribulose-1,5-bisphosphate in the Calvin cycle.
13. The major site of gluconeogenesis in the body is:
A. Brain B. Muscle
C. Liver
D. Pancreas The liver is the primary organ responsible for producing glucose from non- carbohydrate sources.
14. Which vitamin is required for the synthesis of coenzyme A?
A. Vitamin B
B. Vitamin B5 (pantothenic acid)
C. Vitamin B D. Vitamin B Pantothenic acid is a precursor to coenzyme A, essential in metabolism.
15. Which of the following best describes a zymogen?
A. An active enzyme
B. An inactive enzyme precursor
C. A substrate analog D. A cofactor Zymogens are inactive forms of enzymes that require cleavage for activation (e.g., trypsinogen).
16. Which lipid is a key component of biological membranes?
A. Triacylglycerol
B. Phospholipid
20. What is the function of DNA ligase?
A. Unwinds DNA
B. Seals nicks in DNA
C. Synthesizes RNA primers D. Synthesizes new DNA strands DNA ligase forms phosphodiester bonds to seal breaks in the DNA backbone.
21. What does amphipathic mean?
A. Hydrophobic only B. Hydrophilic only
C. Has both hydrophobic and hydrophilic regions
D. Non-polar Amphipathic molecules like phospholipids contain both polar and non-polar regions.
22. Which of the following processes requires oxygen?
A. Glycolysis
B. Electron transport chain
C. Fermentation D. Gluconeogenesis The electron transport chain uses oxygen as the final electron acceptor.
23. The function of chaperones is to:
A. Degrade misfolded proteins B. Catalyze chemical reactions
C. Assist in protein folding
D. Cleave signal peptides Molecular chaperones assist proteins in reaching their correct conformation.
24. Which metabolic pathway generates the most ATP?
A. Glycolysis B. TCA cycle
C. Oxidative phosphorylation
D. Gluconeogenesis Oxidative phosphorylation, driven by the proton gradient, yields the most ATP.
25. What is the structure of an alpha-helix stabilized by?
A. Ionic bonds B. Disulfide bridges
C. Hydrogen bonds
D. Van der Waals interactions Hydrogen bonding between the carbonyl and amide groups stabilizes alpha- helices.
26. Which enzyme catalyzes the first step of glycolysis?
A. Pyruvate kinase
B. Hexokinase
C. Phosphofructokinase D. Aldolase
C. kcat D. Turnover number Competitive inhibitors increase Km but do not affect Vmax.
31. Which molecule initiates the TCA cycle by combining with oxaloacetate?
A. Pyruvate B. Glucose
C. Acetyl-CoA
D. Succinyl-CoA Acetyl-CoA condenses with oxaloacetate to form citrate, starting the TCA cycle.
32. Which class of enzyme catalyzes oxidation-reduction reactions?
A. Hydrolases B. Transferases
C. Oxidoreductases
D. Isomerases Oxidoreductases facilitate electron transfer in redox reactions.
33. The sugar component of RNA is:
A. Deoxyribose
B. Ribose
C. Fructose D. Galactose RNA contains ribose, which has a hydroxyl group at the 2’ carbon.
34. What type of bond links monosaccharides in disaccharides?
A. Peptide bond
B. Glycosidic bond
C. Hydrogen bond D. Phosphodiester bond Glycosidic bonds form between hydroxyl groups of monosaccharides.
35. The central dogma of molecular biology describes:
A. Protein → RNA → DNA B. DNA → Protein → RNA
C. DNA → RNA → Protein
D. RNA → DNA → Protein The central dogma states that genetic information flows from DNA to RNA to protein.
36. Which enzyme relieves supercoiling during DNA replication?
A. Helicase
B. Topoisomerase
C. Primase D. Ligase Topoisomerases cut and rejoin DNA strands to relieve torsional stress.
37. Which process generates NADPH and ribose- 5 - phosphate?
A. Glycolysis
B. Pentose phosphate pathway
C. Beta-oxidation
41. What type of enzyme inhibitor binds only to the enzyme-substrate complex?
A. Competitive B. Noncompetitive
C. Uncompetitive
D. Allosteric Uncompetitive inhibitors bind exclusively to the enzyme-substrate complex, lowering both Km and Vmax.
42. Which is a ketogenic amino acid?
A. Serine B. Glutamate
C. Leucine
D. Asparagine Leucine is purely ketogenic, contributing only to acetyl-CoA or ketone bodies.
43. During translation, which site on the ribosome holds the growing polypeptide
chain? A. A site
B. P site
C. E site D. T site The P site (peptidyl site) holds the tRNA with the growing peptide chain.
44. What molecule donates methyl groups in many biosynthetic reactions?
A. NADH
B. S-adenosylmethionine (SAM)
C. ATP
D. Coenzyme Q SAM is a common methyl donor in methylation reactions.
45. What is the final electron acceptor in the electron transport chain?
A. NAD⁺
B. FAD
C. O₂
D. CO₂
Oxygen accepts electrons at the end of the chain, forming water.
46. Which enzyme is responsible for synthesizing RNA primers?
A. DNA polymerase B. Ligase
C. Primase
D. Helicase Primase lays down short RNA primers to initiate DNA synthesis.
47. Which of the following lipids is a precursor of steroid hormones?
A. Phosphatidylcholine B. Sphingomyelin
C. Cholesterol
D. Triacylglycerol Cholesterol serves as the biosynthetic precursor for all steroid hormones.
48. What does "allosteric regulation" involve?
A. Binding at the active site
D. Coenzyme A PLP (derived from vitamin B6) is essential for transferring amino groups.
52. Which nucleotide base pairs with adenine in RNA?
A. Thymine
B. Uracil
C. Guanine D. Cytosine In RNA, uracil replaces thymine and pairs with adenine.
53. Which molecule is the primary carbon source for the Calvin cycle?
A. O₂
B. CO₂
C. H₂O
D. Glucose The Calvin cycle incorporates CO₂ into organic molecules through carbon fixation.
54. Which enzyme complex connects glycolysis to the TCA cycle?
A. ATP synthase
B. Pyruvate dehydrogenase complex (PDC)
C. Citrate synthase D. Succinate dehydrogenase PDC converts pyruvate into acetyl-CoA, linking glycolysis to the TCA cycle.
55. Which of the following bases is only found in DNA?
A. Uracil
B. Thymine
C. Cytosine D. Adenine Thymine is found only in DNA; uracil replaces it in RNA.
56. Which of these best describes the genetic code?
A. Random and overlapping B. Each codon codes for multiple amino acids
C. Degenerate and non-overlapping
D. Redundant and ambiguous The code is degenerate (multiple codons per amino acid) but each codon is read independently (non-overlapping).
57. What happens during oxidative deamination?
A. Addition of NH₄⁺
B. Removal of an amino group as NH₄⁺
C. Addition of phosphate D. Oxidation of fatty acids Oxidative deamination removes an amino group from an amino acid, releasing ammonia.
58. Which of the following is an essential amino acid?
A. Alanine
B. Lysine
C. Tyrosine D. Glutamine Lysine cannot be synthesized by humans and must be obtained from the diet.
62. What reaction does ATP synthase catalyze?
A. ATP → ADP + Pi
B. ADP + Pi → ATP
C. FAD → FADH₂
D. NADH → NAD⁺
ATP synthase synthesizes ATP from ADP and inorganic phosphate using the proton gradient.
63. What is the function of carnitine in metabolism?
A. Activates glycolysis B. Carries amino acids
C. Transports fatty acids into mitochondria
D. Generates NADPH Carnitine shuttles long-chain fatty acids across the mitochondrial membrane for β- oxidation.
64. What is the fate of pyruvate under anaerobic conditions in muscle cells?
A. Acetyl-CoA B. Ethanol
C. Lactate
D. Oxaloacetate In anaerobic muscle, pyruvate is reduced to lactate to regenerate NAD⁺ for glycolysis.
65. Which of the following cofactors is part of NAD⁺?
A. Riboflavin
B. Biotin
C. Niacin
D. Thiamine Niacin (vitamin B3) is the precursor for NAD⁺, a key redox cofactor.
66. What type of reaction is catalyzed by kinases?
A. Redox
B. Phosphorylation
C. Hydrolysis D. Isomerization Kinases transfer phosphate groups from ATP to substrates.
67. Which of the following best describes the role of oxygen in cellular
respiration? A. ATP donor B. Reducing agent
C. Final electron acceptor
D. Coenzyme Oxygen accepts electrons at the end of the electron transport chain to form water.
68. Which coenzyme is required for decarboxylation reactions?
A. Biotin
B. Thiamine pyrophosphate (TPP)
C. FAD
D. CoA
