Multiple Choice Practice Exam PDF

PRACTICE EXAM What is responsible for water’s high boiling point? A) The low density of water B) The presence of hydrogen bonds C) The absence of oxygen D) The weak attraction between molecules ​ Which weak interaction stabilizes DNA base stacking? A) Hydrogen bonding B) Van der Waals inter...

PRACTICE EXAM What is responsible for water’s high boiling point? A) The low density of water B) The presence of hydrogen bonds C) The absence of oxygen D) The weak attraction between molecules ​ Which weak interaction stabilizes DNA base stacking? A) Hydrogen bonding B) Van der Waals interactions C) Ionic interactions D) Metallic bonding ​ Why do van der Waals interactions occur? A) Due to permanent dipoles in molecules B) Due to temporary dipoles from electron movement C) Due to repulsion between electrons D) Due to hydrogen bonding ​ Which type of interaction occurs between charged species or between ions and dipoles? A) Van der Waals forces B) Ionic (Coulombic) interactions C) Metallic bonds D) Covalent bonds Which law of thermodynamics states that energy cannot be created or destroyed, only transformed? A) First Law B) Second Law C) Third Law D) Zeroth Law ​ The Second Law of Thermodynamics states that: A) Energy is always conserved B) The entropy of an isolated system always increases C) The entropy of a system remains constant D) Chemical reactions never reach equilibrium What is Gibbs free energy (ΔG)? A) The total energy in a system B) The energy available to do work C) The amount of heat released in a reaction D) The number of molecules in a reaction ​ 2A reaction is considered spontaneous when: A) ΔG > 0 B) ΔG = 0 C) ΔG < 0 D) The reaction rate is high ​ What does a catalyst do in a chemical reaction? A) Increases activation energy B) Decreases activation energy C) Changes the equilibrium constant D) Prevents the reaction from proceeding ​ If a reaction has a large negative ΔG, what can be inferred? A) The reaction is at equilibrium B) The reaction is spontaneous and releases energy C) The reaction requires input energy to proceed D) The reaction has stopped ​ What is an exergonic reaction? A) A reaction that absorbs energy B) A reaction that releases energy C) A reaction that never reaches equilibrium D) A reaction with no change in energy ​ What happens in an endergonic reaction? A) Energy is released B) Energy is absorbed C) Entropy decreases D) ΔG is negative ​ Which factor does NOT influence reaction rate? A) Temperature B) Enzyme presence C) Concentration of reactants D) The number of electrons in an atom ​ What term describes the amount of energy required for a reaction to proceed? A) Free energy B) Activation energy C) Kinetic energy D) Potential energy ​ What are the monomers that make up proteins? A) Monosaccharides B) Amino acids C) Nucleotides D) Fatty acids ​ How many standard amino acids are used in protein synthesis? A) 10 B) 15 C) 20 D) 25 ​ What type of bond links amino acids together? A) Hydrogen bond B) Ionic bond C) Peptide bond D) Van der Waals interaction ​ Which level of protein structure describes the linear sequence of amino acids? A) Primary B) Secondary C) Tertiary D) Quaternary ​ Alpha-helices and beta-sheets are stabilized primarily by: A) Covalent bonds B) Hydrogen bonds C) Ionic bonds D) Hydrophobic interactions ​ Which level of protein structure is determined by interactions between R-groups? A) Primary B) Secondary C) Tertiary D) Quaternary ​ Hemoglobin is an example of a protein with which level of structure? A) Primary B) Secondary C) Tertiary D) Quaternary ​ Denaturation of a protein disrupts which structures? A) Primary only B) Secondary, tertiary, and quaternary C) Only tertiary D) None of the above ​ What is the role of chaperone proteins? A) To degrade misfolded proteins B) To assist in protein folding C) To form peptide bonds D) To transport oxygen in the blood ​ What is the effect of increasing temperature on enzyme activity? A) Enzyme activity always increases B) Enzyme activity decreases after an optimal temperature is exceeded C) Enzyme activity is not affected by temperature D) Enzymes are destroyed by low temperatures Section 7: Enzyme Kinetics and Regulation ​ What is an enzyme? A) A protein that slows down chemical reactions B) A lipid that stores energy C) A biological catalyst that speeds up reactions D) A carbohydrate used for energy storage ​ The active site of an enzyme: A) Is where substrates bind B) Changes the enzyme’s primary structure C) Can only bind one specific molecule D) Is identical in all enzymes ​ What does the Michaelis constant (Km) represent? A) The substrate concentration at which the reaction rate is maximal B) The substrate concentration at half the maximum reaction rate C) The maximum velocity of the enzyme D) The total amount of enzyme present ​ What happens when an enzyme reaches Vmax? A) The enzyme is no longer functional B) All enzyme active sites are saturated with substrate C) The reaction stops D) The substrate concentration is zero ​ What is competitive inhibition? A) When an inhibitor binds to the enzyme-substrate complex B) When an inhibitor binds to the active site, blocking the substrate C) When an inhibitor binds to an allosteric site D) When the enzyme denatures ​ What is noncompetitive inhibition? A) An inhibitor that binds to the active site B) An inhibitor that binds to an allosteric site, reducing enzyme activity C) An inhibitor that permanently deactivates an enzyme D) An inhibitor that increases enzyme activity ​ How does allosteric regulation affect enzyme activity? A) It only inhibits enzyme activity B) It can activate or inhibit enzyme activity C) It permanently disables enzymes D) It only increases reaction rates ​ Which molecule often acts as an enzyme cofactor? A) Glucose B) ATP C) Metal ions (such as Mg²⁺ or Zn²⁺) D) Lipids ​ Which type of enzyme regulation involves a molecule binding at a site other than the active site? A) Competitive inhibition B) Allosteric regulation C) Feedback inhibition D) Substrate-level phosphorylation ​ Which metabolic pathway is an example of feedback inhibition? A) Glycolysis B) Fermentation C) Citric Acid Cycle D) All of the above What is the primary purpose of glycolysis? A) To generate ATP and pyruvate B) To break down fatty acids C) To convert ATP into glucose D) To produce oxygen ​ Where does glycolysis occur in the cell? A) Mitochondria B) Cytoplasm C) Nucleus D) Endoplasmic reticulum ​ The net production of ATP per glucose molecule during glycolysis is: A) 1 ATP B) 2 ATP C) 4 ATP D) 6 ATP ​ Which enzyme catalyzes the first committed step of glycolysis? A) Hexokinase B) Phosphofructokinase-1 (PFK-1) C) Pyruvate kinase D) Lactate dehydrogenase ​ What is the fate of pyruvate under anaerobic conditions in muscle cells? A) It is converted to lactate B) It enters the citric acid cycle C) It is converted to acetyl-CoA D) It is used to produce urea ​ In which cellular compartment does the citric acid cycle occur? A) Cytoplasm B) Nucleus C) Mitochondrial matrix D) Endoplasmic reticulum ​ What is the primary function of the citric acid cycle? A) To generate ATP directly B) To produce high-energy electron carriers (NADH, FADH₂) C) To store glucose D) To break down fatty acids ​ Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA? A) Pyruvate kinase B) Lactate dehydrogenase C) Pyruvate dehydrogenase D) Citrate synthase ​ Which metabolic process generates the most ATP? A) Glycolysis B) Citric acid cycle C) Oxidative phosphorylation D) Fermentation ​ In oxidative phosphorylation, the final electron acceptor in the electron transport chain is: A) NADH B) ATP C) Oxygen D) Carbon dioxide Section 9: Nucleic Acids and DNA Replication ​ What is the monomer unit of nucleic acids? A) Amino acid B) Nucleotide C) Monosaccharide D) Fatty acid ​ Which nitrogenous base is found in RNA but not in DNA? A) Adenine B) Thymine C) Guanine D) Uracil ​ DNA replication is described as: A) Conservative B) Semiconservative C) Dispersive D) Random ​.​ Which enzyme unwinds the DNA double helix during replication? A) DNA ligase B) DNA polymerase C) Helicase D) Primase What is the role of DNA polymerase? A) To synthesize new DNA strands B) To unwind the DNA helix C) To join Okazaki fragments D) To remove RNA primers ​ The leading strand in DNA replication is synthesized: A) Discontinuously B) In short fragments C) Continuously D) From 3’ to 5’ ​ Okazaki fragments are associated with: A) The leading strand B) The lagging strand C) RNA transcription D) Protein translation ​ Which enzyme joins Okazaki fragments together? A) DNA helicase B) DNA ligase C) DNA polymerase D) Primase ​ The central dogma of molecular biology states that genetic information flows from: A) Protein → RNA → DNA B) RNA → DNA → Protein C) DNA → RNA → Protein D) DNA → Protein → RNA ​ What process converts RNA into protein? A) Replication B) Transcription C) Translation D) Reverse transcription ​ What type of macromolecule are phospholipids? A) Carbohydrates B) Proteins C) Lipids D) Nucleic acids ​ Which part of a phospholipid is hydrophobic? A) The phosphate head B) The glycerol backbone C) The fatty acid tails D) The entire molecule ​ The plasma membrane is described by the: A) Fluid mosaic model B) Lock and key model C) Charged particle model D) Central dogma ​ Cholesterol in the cell membrane serves to: A) Increase permeability B) Decrease membrane fluidity at high temperatures C) Prevent protein synthesis D) Transport glucose ​ Integral membrane proteins are: A) Only found on the membrane surface B) Embedded within the lipid bilayer C) Soluble in water D) Composed of carbohydrates ​ What type of transport requires ATP? A) Passive diffusion B) Facilitated diffusion C) Active transport D) Osmosis ​ The sodium-potassium pump moves: A) 2 Na⁺ out, 3 K⁺ in B) 3 Na⁺ out, 2 K⁺ in C) 2 K⁺ out, 3 Na⁺ in D) 3 K⁺ out, 2 Na⁺ in ​ Which molecule can diffuse freely across the plasma membrane? A) Glucose B) Na⁺ ions C) Oxygen D) ATP ​ Which process engulfs large particles into the cell? A) Exocytosis B) Pinocytosis C) Phagocytosis D) Facilitated diffusion ​ What is the main function of lipid rafts in membranes? A) Protein degradation B) Signal transduction and membrane trafficking C) DNA replication D) Cell division.Which type of signaling involves hormones traveling through the bloodstream? A) Paracrine signaling B) Endocrine signaling C) Autocrine signaling D) Synaptic signaling ​ What type of receptor binds hydrophobic ligands such as steroid hormones? A) G-protein coupled receptors (GPCRs) B) Ion channel receptors C) Intracellular receptors D) Tyrosine kinase receptors ​ The role of a second messenger in cell signaling is to: A) Directly bind DNA B) Activate G-proteins C) Relay and amplify a signal inside the cell D) Synthesize proteins ​ What is an oncogene? A) A gene that promotes apoptosis B) A gene that suppresses tumors C) A mutated gene that promotes cancer growth D) A gene that codes for histones ​ Apoptosis is: A) Uncontrolled cell division B) Programmed cell death C) DNA replication D) ATP production PRACTICE EXAM 2 What determines a protein’s function? A) Its amino acid composition B) Its three-dimensional structure C) The number of disulfide bonds D) Its molecular weight What is the “native fold” of a protein? A) The most unstable structure B) A random coil of the polypeptide C) The specific, stable structure a protein assumes to function D) The structure a protein adopts in a denatured state Which of the following is NOT a key non-covalent interaction stabilizing protein structure? A) Hydrophobic effect B) Hydrogen bonds C) Covalent bonds D) Van der Waals interactions How does the hydrophobic effect contribute to protein folding? A) It causes hydrophobic amino acids to cluster in the protein interior B) It stabilizes the protein by forming ionic bonds C) It increases the entropy of the protein itself D) It strengthens covalent peptide bonds What type of non-covalent interaction stabilizes alpha-helices and beta-sheets? A) Electrostatic interactions B) Van der Waals forces C) Hydrogen bonds D) Hydrophobic interactions Van der Waals interactions in proteins are best described as: A) Strong ionic attractions between charged groups B) Weak attractions between all atoms that stabilize the protein’s interior C) The driving force for protein folding D) A type of covalent bonding Electrostatic interactions are strongest when: A) They occur in a hydrophobic environment B) The protein is in a highly hydrated state C) The interacting groups are nonpolar D) There are no salt bridges present Protein Structural Hierarchy What is the primary structure of a protein? A) The sequence of amino acids B) The arrangement of alpha-helices and beta-sheets C) The overall 3D shape of a polypeptide D) The association of multiple subunits What defines secondary structure in proteins? A) The sequence of amino acids B) The interactions between protein domains C) Local folding into alpha-helices and beta-sheets D) The quaternary arrangement of polypeptides Which amino acid is a known “helix breaker”? A) Alanine B) Leucine C) Glycine D) Valine What type of bond stabilizes beta-turns? A) Covalent bonds B) Hydrogen bonds C) Peptide bonds D) Ionic bonds What does the Ramachandran plot illustrate? A) The hydrogen bonding pattern of beta-sheets B) The allowed and disallowed dihedral angles in a protein backbone C) The free energy of folding D) The effect of heat on protein stability ​ Which protein structure classification includes water-soluble proteins with complex folding? A) Fibrous proteins B) Globular proteins C) Lipid-soluble membrane proteins D) Disordered proteins Fibrous Proteins and Examples ​ Which of the following is an example of a fibrous protein? A) Myoglobin B) Hemoglobin C) Collagen D) Troponin ​ What structural feature of silk fibroin makes it soft and flexible? A) Cross-linked alpha-helices B) Triple-helical structure C) Beta-sheets held together by van der Waals interactions D) High cysteine content Protein Folding and Stability ​ What is the main driving force behind protein folding? A) Hydrogen bonding B) Peptide bond formation C) The hydrophobic effect D) Electrostatic interactions ​ Which experiment demonstrated that proteins can spontaneously refold into their native conformation? A) Meselson-Stahl experiment B) Anfinsen’s ribonuclease experiment C) Hershey-Chase experiment D) Avery-MacLeod-McCarty experiment ​ Which method is NOT used to determine protein structure? A) X-ray crystallography B) Cryo-electron microscopy C) Computational structure prediction D) NMR spectroscopy Reversible Ligand Binding & Hemoglobin/Myoglobin ​ What is a ligand? A) A protein subunit B) A molecule that binds to a protein C) A type of amino acid D) A type of nucleic acid ​ What does a lower dissociation constant (Kd) indicate? A) Weaker ligand binding B) Stronger ligand binding C) Higher entropy D) No binding occurs ​ What is the function of myoglobin? A) Oxygen transport in the blood B) Breaking down proteins C) Storing oxygen in muscle tissue D) Forming part of the immune system ​ What is the quaternary structure of hemoglobin? A) A single polypeptide chain B) A dimer C) A tetramer (α2β2) D) An octamer ​ What is the T-state of hemoglobin? A) The high-affinity oxygen-binding state B) The state where hemoglobin is fully oxygenated C) The low-affinity oxygen-binding state D) A completely unfolded state ​ How does cooperative binding in hemoglobin function? A) Oxygen binding increases the affinity of other subunits for oxygen B) Oxygen binding causes hemoglobin to release CO2 C) Oxygen binding prevents further oxygen from binding D) Each subunit binds oxygen independently What determines a protein’s function? a) Its amino acid sequence b) Its three-dimensional structure c) The number of disulfide bonds d) The hydrophobic residues it contains ​ What is the “native fold” of a protein? a) The unfolded, inactive state of a protein b) The specific, stable 3D structure a protein adopts to function c) A temporary intermediate conformation d) A completely random structure ​ Which of the following is NOT a non-covalent interaction that stabilizes protein structure? a) Hydrophobic effect b) Hydrogen bonds c) Peptide bonds d) Electrostatic interactions ​ What is the primary driving force for protein folding? a) Hydrogen bonding b) Hydrophobic effect c) Van der Waals interactions d) Electrostatic interactions ​ Hydrogen bonds in proteins primarily occur between: a) Nonpolar amino acids b) N-H and C=O groups of the peptide bond c) Sulfur atoms in cysteine residues d) Hydrophobic side chains Van der Waals interactions in protein interiors contribute to: a) Covalent cross-linking b) Medium-range weak attraction between all atoms c) Strong electrostatic bonding d) Hydrophobic repulsion ​ What type of interaction is responsible for salt bridges in proteins? a) Hydrogen bonding b) Hydrophobic effect c) Electrostatic interactions d) Van der Waals forces Structural Hierarchy ​ What is the first level of protein structural organization? a) Secondary structure b) Primary structure c) Tertiary structure d) Quaternary structure ​ Alpha-helices are stabilized by: a) Peptide bonds between amino acid side chains b) Hydrogen bonds between backbone N-H and C=O groups c) Disulfide bonds between cysteine residues d) Hydrophobic interactions ​ Which of the following amino acids is known to disrupt alpha-helix formation? a) Alanine b) Leucine c) Glycine d) Serine ​ Beta-sheets can be arranged in what two forms? a) Random and looped b) Coiled and extended c) Parallel and antiparallel d) Right-handed and left-handed ​ A beta-turn consists of how many amino acids? a) 2 b) 3 c) 4 d) 5 Which amino acid is commonly found in position 2 of a beta-turn? a) Glycine b) Proline c) Alanine d) Valine ​ What characteristic makes the peptide bond rigid? a) Its single bond character b) Its partial double bond character c) Its ability to rotate freely d) Its weak hydrogen bonding ability ​ Which two dihedral angles define the conformation of the polypeptide backbone? a) Theta (θ) and phi (φ) b) Phi (φ) and psi (ψ) c) Sigma (σ) and tau (τ) d) Omega (ω) and rho (ρ) ​ The Ramachandran plot is used to: a) Determine amino acid sequences b) Show favorable phi (φ) and psi (ψ) angle combinations c) Predict the molecular weight of proteins d) Identify disulfide bonds Protein Classification Fibrous proteins are typically: a) Water-soluble b) Globular in shape c) Insoluble and made of one secondary structure d) Found only in enzymes ​ What type of protein is silk fibroin? a) Globular b) Fibrous c) Disordered d) Membrane-bound ​ What type of interactions hold silk fibroin together? a) Disulfide bonds b) Van der Waals forces c) Ionic bonds d) Hydrogen bonds ​ Which fibrous protein has cross-linked triple helices for tensile strength? a) Alpha-keratin b) Silk fibroin c) Collagen d) Myosin ​ What did Anfinsen’s experiment with ribonuclease demonstrate? a) The sequence alone determines the native conformation b) Proteins require chaperones to fold correctly c) Disulfide bonds are the primary determinant of protein structure d) Denatured proteins cannot refold spontaneously ​ Which of the following can denature a protein? a) Heat b) pH extremes c) Urea d) All of the above ​ How does guanidinium hydrochloride denature proteins? a) By disrupting hydrogen bonds b) By stabilizing disulfide bonds c) By promoting hydrophobic interactions d) By strengthening ionic bonds Ligand Binding and Cooperativity ​ A ligand binds to a protein at its: a) Active site b) Hydrophobic core c) Binding site d) C-terminal ​ What does a low dissociation constant (Kd) indicate? a) Weak ligand binding b) Strong ligand binding c) No ligand binding d) Denaturation of the protein ​ What model assumes the protein binding site is pre-formed and does not change upon ligand binding? a) Induced fit model b) Lock-and-key model c) Sequential binding model d) Allosteric model ​ In the induced fit model of ligand binding: a) The protein structure changes upon ligand binding b) The ligand binds irreversibly c) The protein structure remains rigid d) The ligand changes its shape to fit the protein ​ Hemoglobin’s oxygen binding curve is: a) Hyperbolic b) Sigmoidal c) Linear d) Parabolic ​ What state of hemoglobin has the lowest oxygen affinity? a) T (tense) state b) R (relaxed) state c) Fully saturated state d) None of the above ​ Allosteric enzymes are typically: a) Monomeric b) Oligomeric c) Unaffected by effectors d) Linear in structure ​ Which type of enzyme inhibitor binds to the active site and competes with the substrate? a) Noncompetitive inhibitor b) Competitive inhibitor c) Uncompetitive inhibitor d) Irreversible inhibitor ​ In a Lineweaver-Burk plot, the y-intercept represents: a) Vmax b) Km c) 1/Vmax d) 1/Km ​ The Michaelis constant () represents: a) The maximum velocity of an enzyme b) The concentration of substrate at which the enzyme operates at half its c) The rate constant of the enzyme reaction d) The equilibrium constant for enzyme-substrate binding ​ A noncompetitive inhibitor affects: a) Only b) Only c) Both and d) Neither nor Hemoglobin and Oxygen Transport ​ The Bohr effect describes how hemoglobin’s oxygen affinity decreases: a) At high pH b) At low CO₂ levels c) At low pH and high CO₂ levels d) In the presence of carbon monoxide ​ What molecule stabilizes the T-state of hemoglobin? a) ATP b) BPG (2,3-bisphosphoglycerate) c) NADH d) Myoglobin ​ Myoglobin is primarily responsible for: a) Oxygen transport in the blood b) Oxygen storage in muscle cells c) Carbon dioxide transport d) Allosteric regulation of hemoglobin ​ Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin because: a) It binds BPG more tightly b) It has a different heme group c) It has a lower affinity for BPG d) It contains fewer subunits Lipids and Membranes ​ Which type of lipid is the primary component of cell membranes? a) Triacylglycerols b) Phospholipids c) Cholesterol d) Sphingolipids ​ Cholesterol in the plasma membrane functions to: a) Increase membrane permeability b) Increase membrane rigidity at high temperatures c) Prevent protein diffusion d) Act as an enzyme ​ Integral membrane proteins differ from peripheral membrane proteins in that they: a) Can be easily removed by changing salt concentration b) Contain hydrophobic transmembrane domains c) Are not associated with the membrane bilayer d) Are only found on the cytoplasmic side Carbohydrates and Metabolism ​ Glycolysis occurs in the: a) Mitochondria b) Cytoplasm c) Nucleus d) Endoplasmic reticulum ​ The enzyme responsible for catalyzing the rate-limiting step of glycolysis is: a) Hexokinase b) Phosphofructokinase-1 (PFK-1) c) Pyruvate kinase d) Aldolase ​ What molecule is the final electron acceptor in the electron transport chain? a) CO₂ b) ATP c) NADH d) O₂ ​ The Cori cycle links which two tissues? a) Brain and heart b) Liver and muscle c) Kidney and pancreas d) Intestine and blood Amino Acid and Nucleotide Metabolism ​ Which amino acid is the precursor for serotonin? a) Tyrosine b) Tryptophan c) Glutamate d) Histidine ​ Which enzyme is the key regulatory step in purine biosynthesis? a) Carbamoyl phosphate synthetase b) PRPP synthetase c) Ribonucleotide reductase d) Adenylate cyclase ​ The urea cycle occurs in the: a) Mitochondria and cytoplasm b) Nucleus c) Golgi apparatus d) Plasma membrane DNA, RNA, and Gene Expression ​ What type of bond holds the two strands of DNA together? a) Covalent bonds b) Hydrogen bonds c) Ionic bonds d) Disulfide bonds ​ Which RNA polymerase is responsible for transcribing mRNA in eukaryotes? a) RNA polymerase I b) RNA polymerase II c) RNA polymerase III d) DNA polymerase ​ In eukaryotic transcription, what is the function of the TATA box? a) It acts as a stop codon b) It recruits RNA polymerase to the promoter c) It signals for RNA splicing d) It prevents translation errors ​ The process of removing introns from pre-mRNA is called: a) Translation b) Splicing c) Transcription d) Capping DNA replication occurs in which phase of the cell cycle? a) G1 phase b) S phase c) G2 phase d) M phase ​ The enzyme that unwinds the DNA double helix during replication is: a) DNA polymerase b) Helicase c) Topoisomerase d) Ligase ​ Okazaki fragments are: a) Leading strand fragments b) Synthesized continuously c) Synthesized on the lagging strand d) Made of RNA ​ Which enzyme is responsible for removing RNA primers in DNA replication? a) DNA polymerase I b) DNA polymerase III c) Ligase d) Primase ​ The enzyme responsible for adding telomeres to the ends of chromosomes is: a) Helicase b) Ligase c) Telomerase d) Exonuclease ​ Mismatch repair fixes errors that occur: a) During DNA replication b) Due to UV radiation c) From oxidative damage d) After transcription RNA Processing and Translation ​ The 5’ cap on eukaryotic mRNA is composed of: a) Adenosine triphosphate b) Guanine triphosphate (GTP) c) Uracil diphosphate d) Cytosine monophosphate ​ The ribosome binds to which region of the mRNA in prokaryotes? a) TATA box b) Shine-Dalgarno sequence c) Kozak sequence d) Poly-A tail ​ The amino acid sequence of a protein is determined by: a) The tRNA anticodon b) The rRNA structure c) The mRNA codon sequence d) The poly-A tail ​ Which of the following best describes the wobble hypothesis? a) A single tRNA can recognize multiple codons b) tRNA binds only to one specific codon c) The ribosome randomly selects amino acids d) Stop codons encode for amino acids ​ In eukaryotic cells, translation occurs in the: a) Nucleus b) Cytoplasm c) Endoplasmic reticulum d) Mitochondria Bioenergetics and Metabolism ​ The enzyme responsible for converting glucose-6-phosphate to fructose-6-phosphate in glycolysis is: a) Hexokinase b) Phosphoglucose isomerase c) Aldolase d) Pyruvate kinase ​ The first step of gluconeogenesis occurs in the: a) Cytoplasm b) Mitochondria c) Nucleus d) Lysosome ​ Which molecule is a key allosteric activator of phosphofructokinase-1 (PFK-1) in glycolysis? a) ATP b) Citrate c) AMP d) NADH ​ The primary regulatory enzyme of the pentose phosphate pathway is: a) Glucose-6-phosphate dehydrogenase b) Pyruvate kinase c) Fructose-1,6-bisphosphatase d) Phosphofructokinase ​ The conversion of pyruvate to acetyl-CoA is catalyzed by: a) Pyruvate carboxylase b) Pyruvate dehydrogenase c) Pyruvate kinase d) Lactate dehydrogenase ​ Which enzyme serves as the rate-limiting step in cholesterol synthesis? a) Acetyl-CoA carboxylase b) HMG-CoA reductase c) Squalene synthase d) Mevalonate kinase ​ The primary effect of glucagon is to: a) Decrease blood glucose levels b) Increase glucose uptake by muscles c) Increase blood glucose levels d) Stimulate glycogen synthesis ​ Which enzyme is activated by cAMP in response to glucagon signaling? a) Phosphofructokinase-1 (PFK-1) b) Protein kinase A (PKA) c) Phospholipase C d) Hexokinase ​ Epinephrine promotes glycogen breakdown by activating which enzyme? a) Glycogen phosphorylase b) Glycogen synthase c) Pyruvate kinase d) Phosphoglucomutase ​ The insulin receptor is classified as a: a) G-protein coupled receptor b) Tyrosine kinase receptor c) Ligand-gated ion channel d) Nuclear receptor ​ In response to insulin signaling, glucose transporters (GLUT4) are translocated to the plasma membrane in: a) Liver cells b) Pancreatic beta cells c) Muscle and adipose cells d) Red blood cells Enzyme Kinetics and Inhibition ​ Which of the following best describes competitive inhibition? a) Inhibitor binds to the active site b) Inhibitor binds to an allosteric site c) Inhibitor forms a covalent bond with the enzyme d) Inhibitor binds to both enzyme and enzyme-substrate complex ​ In non-competitive inhibition, the inhibitor: a) Lowers Vmax but does not change Km b) Increases both Vmax and Km c) Lowers Km but does not change Vmax d) Increases Km but does not change Vmax ​ The Michaelis-Menten constant (Km) represents: a) The substrate concentration at which the reaction rate is maximal b) The substrate concentration at which the reaction rate is half-maximal c) The maximum velocity of an enzyme-catalyzed reaction d) The rate of product formation ​ A Lineweaver-Burk plot is useful for determining: a) Vmax and Km b) Enzyme concentration c) Substrate turnover number d) Activation energy ​ The turnover number (kcat) of an enzyme represents: a) The rate of substrate binding b) The number of substrate molecules converted to product per enzyme molecule per second c) The maximum reaction velocity d) The energy required for catalysis Lipid Metabolism ​ The rate-limiting enzyme in fatty acid synthesis is: a) Acetyl-CoA carboxylase b) Carnitine acyltransferase I c) HMG-CoA synthase d) Fatty acid synthase ​ β-oxidation of fatty acids occurs in the: a) Cytoplasm b) Mitochondrial matrix c) Endoplasmic reticulum d) Peroxisomes ​ The transport of fatty acids into the mitochondria for β-oxidation requires: a) Acetyl-CoA b) Carnitine c) Malonyl-CoA d) NADPH Ketone bodies are produced in which organ during prolonged fasting? a) Liver b) Muscle c) Brain d) Kidney ​ Which ketone body is not used for energy production? a) Acetoacetate b) β-Hydroxybutyrate c) Acetone d) Both acetoacetate and β-hydroxybutyrate Amino Acid and Nitrogen Metabolism ​ The urea cycle occurs primarily in which organ? a) Kidney b) Liver c) Pancreas d) Muscle ​ The rate-limiting enzyme of the urea cycle is: a) Arginase b) Carbamoyl phosphate synthetase I c) Ornithine transcarbamylase d) Argininosuccinate synthetase ​ The primary carrier of nitrogen in the blood is: a) Alanine b) Glutamine c) Aspartate d) Serine ​ Which of the following amino acids is purely ketogenic? a) Alanine b) Arginine c) Leucine d) Glutamate ​ Transamination reactions require which coenzyme? a) NAD+ b) FAD c) Pyridoxal phosphate (PLP) d) Coenzyme A Miscellaneous Biochemical Concepts ​ Which vitamin is necessary for collagen synthesis? a) Vitamin A b) Vitamin B6 c) Vitamin C d) Vitamin D ​ Which of the following is a function of glutathione? a) DNA replication b) Protein degradation c) Antioxidant defense d) Electron transport ​ The Bohr effect describes: a) The effect of temperature on enzyme activity b) The influence of pH and CO₂ on hemoglobin’s oxygen affinity c) The breakdown of glucose under anaerobic conditions d) The conversion of lactate to pyruvate ​ In which form is iron stored in the body? a) Transferrin b) Ferritin c) Hemoglobin d) Myoglobin ​ Which of the following is a second messenger in calcium signaling? a) cAMP b) Inositol triphosphate (IP3) c) ATP d) NADH