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Make 100 mcqs on biochemical organization of cell membrane and apoptosis of biochemistry for medical students to pass exam

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I have sufficient textbook material from Robbins, Guyton, and Histology. Now I'll compile all 100 MCQs.

100 MCQs: Biochemical Organization of Cell Membrane & Apoptosis

Section A: Biochemical Organization of the Cell Membrane (Q1–50)

Q1. The approximate lipid composition of the cell membrane includes which of the following percentages for phospholipids?
  • A) 13%
  • B) 25% ✓
  • C) 40%
  • D) 55%
  • E) 3%
Answer: B — 25% The cell membrane is ~55% proteins, 25% phospholipids, 13% cholesterol, 4% other lipids, and 3% carbohydrates. (Guyton & Hall)
Q2. The cell membrane thickness is approximately:
  • A) 1–2 nm
  • B) 3–5 nm
  • C) 7.5–10 nm ✓
  • D) 15–20 nm
  • E) 25–30 nm
Answer: C — 7.5–10 nm The cell membrane is a thin, pliable, elastic structure only 7.5 to 10 nanometers thick. (Guyton & Hall)
Q3. Which of the following is the MOST abundant lipid in the cell membrane?
  • A) Cholesterol
  • B) Sphingolipids
  • C) Phospholipids ✓
  • D) Glycolipids
  • E) Triglycerides
Answer: C — Phospholipids Phospholipids are the most abundant cell membrane lipids. (Guyton & Hall)
Q4. The basic structural framework of the cell membrane is:
  • A) A protein scaffold
  • B) A lipid bilayer ✓
  • C) A glycocalyx
  • D) A cholesterol monolayer
  • E) A collagen matrix
Answer: B — A lipid bilayer Its basic structure is a lipid bilayer — a thin, double-layered film of lipids, each layer only one molecule thick. (Guyton & Hall)
Q5. The hydrophilic portion of a phospholipid molecule is:
  • A) Fatty acid chains
  • B) Steroid nucleus
  • C) Phosphate head group ✓
  • D) Ceramide backbone
  • E) Glycerol only
Answer: C — Phosphate head group The phosphate end of each phospholipid molecule is hydrophilic and soluble in water. (Guyton & Hall)
Q6. Which of the following substances can easily penetrate the lipid bilayer of the cell membrane?
  • A) Glucose
  • B) Sodium ions
  • C) Urea
  • D) Oxygen ✓
  • E) Proteins
Answer: D — Oxygen Fat-soluble substances such as oxygen, carbon dioxide, and alcohol can penetrate this portion of the membrane with ease. (Guyton & Hall)
Q7. Which of the following substances CANNOT readily cross the lipid bilayer?
  • A) Carbon dioxide
  • B) Alcohol
  • C) Glucose ✓
  • D) Oxygen
  • E) Steroids
Answer: C — Glucose The lipid layer in the middle is impermeable to the usual water-soluble substances, such as ions, glucose, and urea. (Guyton & Hall)
Q8. Sphingolipids are derived from which amino alcohol?
  • A) Serine
  • B) Ethanolamine
  • C) Sphingosine ✓
  • D) Choline
  • E) Glycerol
Answer: C — Sphingosine Sphingolipids, derived from the amino alcohol sphingosine, also have hydrophobic and hydrophilic groups. (Guyton & Hall)
Q9. Complex sphingolipids in cell membranes serve all of the following functions EXCEPT:
  • A) Protection from harmful environmental factors
  • B) Signal transmission
  • C) Adhesion sites for extracellular proteins
  • D) Energy storage ✓
  • E) Both hydrophobic and hydrophilic properties
Answer: D — Energy storage Sphingolipids serve functions including protection, signal transmission, and adhesion sites, but not energy storage. (Guyton & Hall)
Q10. The role of cholesterol in the cell membrane includes:
  • A) Providing the main structural backbone
  • B) Forming channels for ion transport
  • C) Determining membrane permeability and fluidity ✓
  • D) Carrying carbohydrate chains
  • E) Anchoring cytoskeletal proteins
Answer: C — Determining membrane permeability and fluidity Cholesterol controls much of the fluidity of the membrane and helps determine the degree of permeability. (Guyton & Hall)
Q11. Cholesterol molecules are classified as lipids because:
  • A) They contain phosphate groups
  • B) Their steroid nuclei are highly fat-soluble ✓
  • C) They have hydrophilic heads
  • D) They are derived from sphingosine
  • E) They form channels in the membrane
Answer: B — Their steroid nuclei are highly fat-soluble Cholesterol molecules are also lipids because their steroid nuclei are highly fat-soluble. (Guyton & Hall)
Q12. Membrane proteins that protrude all the way through the lipid bilayer are called:
  • A) Peripheral proteins
  • B) Glycoproteins
  • C) Integral proteins ✓
  • D) Extrinsic proteins
  • E) Cytoskeletal proteins
Answer: C — Integral proteins Integral proteins protrude all the way through the membrane; peripheral proteins are attached only to one surface. (Guyton & Hall)
Q13. Peripheral membrane proteins are primarily associated with the membrane by:
  • A) Hydrophobic interactions with the lipid core
  • B) Strong ionic interactions, mainly with integral proteins ✓
  • C) Covalent bonds with cholesterol
  • D) Van der Waals forces with sphingolipids
  • E) Disulfide bonds
Answer: B — Strong ionic interactions with integral proteins Peripheral proteins are associated with the plasma membrane by strong ionic interactions, mainly with integral proteins. (Histology, Wheater)
Q14. The current interpretation of the molecular organization of the plasma membrane is referred to as:
  • A) The unit membrane model
  • B) The sandwich model
  • C) The modified fluid-mosaic model ✓
  • D) The lipid crystal model
  • E) The bilayer lattice model
Answer: C — The modified fluid-mosaic model The current interpretation of the molecular organization of the plasma membrane is referred to as the modified fluid-mosaic model. (Histology)
Q15. In the fluid-mosaic model, lipid molecules:
  • A) Are fixed in position
  • B) Can diffuse laterally within their leaflet ✓
  • C) Can flip-flop freely between leaflets
  • D) Are immobile at physiological temperatures
  • E) Are arranged in a crystalline lattice
Answer: B — Can diffuse laterally within their leaflet Individual lipids can diffuse laterally within a leaflet of the bilayer, giving the membrane its fluid character.
Q16. Glycoproteins on the extracellular surface of the cell membrane are formed by:
  • A) Cholesterol attached to proteins
  • B) Phospholipids attached to proteins
  • C) Carbohydrates attached to proteins ✓
  • D) Sphingolipids attached to proteins
  • E) Fatty acids attached to proteins
Answer: C — Carbohydrates attached to proteins Carbohydrates may be attached to proteins, thereby forming glycoproteins, or to lipids, forming glycolipids. (Histology)
Q17. The glycocalyx refers to:
  • A) The inner leaflet of the membrane bilayer
  • B) The carbohydrate-rich coat on the extracellular surface ✓
  • C) The cytoskeletal network beneath the membrane
  • D) The lipid raft microdomain
  • E) The cholesterol-rich core of the membrane
Answer: B — Carbohydrate-rich coat on the extracellular surface Glycoproteins of the glycocalyx can be seen extending from the cell surface into the extracellular space. (Histology)
Q18. Lipid rafts are characterized by high concentrations of:
  • A) Phosphatidylcholine and triglycerides
  • B) Glycosphingolipids and cholesterol ✓
  • C) Phosphatidylserine and calcium
  • D) Cardiolipin and protein kinases
  • E) Ceramide and sphingomyelin only
Answer: B — Glycosphingolipids and cholesterol Lipid rafts are characterized by a high concentration of glycosphingolipids and cholesterol, containing large numbers of integral and peripheral membrane proteins. (Histology)
Q19. Which leaflet of the cell membrane normally contains phosphatidylserine in healthy cells?
  • A) Outer leaflet
  • B) Inner (cytoplasmic) leaflet ✓
  • C) Equally distributed in both leaflets
  • D) Only in the hydrophobic core
  • E) Associated with the glycocalyx
Answer: B — Inner (cytoplasmic) leaflet In healthy cells, phosphatidylserine is present on the inner leaflet of the plasma membrane. (Robbins)
Q20. The asymmetric distribution of lipids between the two membrane leaflets:
  • A) Is determined solely by cholesterol
  • B) Reflects a steady state involving constant lipid exchange ✓
  • C) Is identical in all biological membranes
  • D) Plays no functional role
  • E) Is maintained by covalent bonds
Answer: B — Reflects a steady state involving constant lipid exchange Lipid asymmetry reflects a steady state involving a constant exchange of phospholipids between the two bilayer hemileaflets. (Goldman-Cecil Medicine)
Q21. In electron microscopy, the cell membrane appears as:
  • A) A single dense line
  • B) Two electron-dense lines separated by an electron-lucent layer ✓
  • C) Three electron-dense bands
  • D) A fuzzy, indistinct border
  • E) A series of electron-lucent rings
Answer: B — Two electron-dense lines separated by an electron-lucent layer At high magnification, the plasma membrane displays two electron-dense lines separated by an electron-lucent intermediate layer. (Histology)
Q22. In most plasma membranes, protein molecules constitute approximately what proportion of total membrane mass?
  • A) 10%
  • B) 25%
  • C) ~50% ✓
  • D) 70%
  • E) 80%
Answer: C — ~50% In most plasma membranes, protein molecules constitute approximately half of the total membrane mass. (Histology)
Q23. Integral membrane proteins are mainly:
  • A) Glycolipids
  • B) Glycoproteins ✓
  • C) Proteoglycans
  • D) Simple proteins without carbohydrate
  • E) Sphingoproteins
Answer: B — Glycoproteins These membrane proteins are mainly glycoproteins. (Guyton & Hall)
Q24. Ion channels through the cell membrane are formed by which type of proteins?
  • A) Peripheral proteins
  • B) Extrinsic proteins
  • C) Integral (transmembrane) proteins ✓
  • D) Cytoskeletal proteins
  • E) Glycolipids
Answer: C — Integral (transmembrane) proteins Many integral proteins provide structural channels (or pores) through which water molecules and ions can diffuse. (Guyton & Hall)
Q25. Which of the following correctly describes the orientation of phospholipid molecules in the bilayer?
  • A) Hydrophilic tails face outward; hydrophobic heads face inward
  • B) Hydrophobic tails face outward on both sides
  • C) Hydrophilic heads form the outer surfaces; hydrophobic tails face each other in the center ✓
  • D) Both heads and tails are randomly distributed
  • E) Heads face inward; tails face outward
Answer: C The hydrophilic phosphate portions constitute the two surfaces, while hydrophobic fatty acid portions are in the middle. (Guyton & Hall)
Q26. The "fluid" property of the cell membrane is primarily maintained by:
  • A) High protein content
  • B) Glycolipid concentration
  • C) Cholesterol and unsaturated fatty acids ✓
  • D) Peripheral protein anchorage
  • E) Disulfide bridges in integral proteins
Answer: C — Cholesterol and unsaturated fatty acids Cholesterol affects the packing of fatty acid chains, with a major effect on membrane fluidity. (Junqueira's Histology)
Q27. The three main types of lipids in the lipid bilayer are:
  • A) Triglycerides, phospholipids, and waxes
  • B) Phospholipids, sphingolipids, and cholesterol ✓
  • C) Cholesterol, glycolipids, and ceramides
  • D) Phosphatidylcholine, phosphatidylserine, and cardiolipin
  • E) Sphingomyelin, lecithin, and sterols
Answer: B — Phospholipids, sphingolipids, and cholesterol The basic lipid bilayer is composed of three main types of lipids — phospholipids, sphingolipids, and cholesterol. (Guyton & Hall)
Q28. The carbohydrate content of the cell membrane is approximately:
  • A) 25%
  • B) 13%
  • C) 4%
  • D) 3% ✓
  • E) 10%
Answer: D — 3% The approximate composition is 55% proteins, 25% phospholipids, 13% cholesterol, 4% other lipids, and 3% carbohydrates. (Guyton & Hall)
Q29. Which membrane component is primarily responsible for cell-to-cell recognition and receptor functions?
  • A) Cholesterol
  • B) Phospholipids
  • C) Glycocalyx (glycoproteins/glycolipids) ✓
  • D) Peripheral proteins
  • E) Integral lipids
Answer: C — Glycocalyx Carbohydrate components of the glycocalyx are involved in cell recognition, adhesion, and receptor functions.
Q30. The outer layer of the cell membrane contains which lipid that is NOT found in the inner leaflet?
  • A) Phosphatidylserine
  • B) Phosphatidylinositol
  • C) Glycolipids ✓
  • D) Cardiolipin
  • E) Phosphatidylethanolamine
Answer: C — Glycolipids The outer layer of the cell membrane also contains glycolipids confined to the extracellular leaflet. (Junqueira's Histology)
Q31. The "mosaic" aspect of the fluid-mosaic model refers to:
  • A) The crystalline structure of the lipid bilayer
  • B) The various proteins scattered throughout the lipid bilayer ✓
  • C) The equal distribution of lipids in both leaflets
  • D) The pattern of carbohydrate chains
  • E) The regular arrangement of cholesterol molecules
Answer: B — Proteins scattered throughout the lipid bilayer The proteins are interspersed in a mosaic pattern throughout the lipid bilayer.
Q32. Membrane channel proteins that allow water to pass are called:
  • A) Sodium pumps
  • B) Aquaporins ✓
  • C) Ionophores
  • D) Porins
  • E) Connexins
Answer: B — Aquaporins Specific water channels (aquaporins) allow rapid water movement across membranes.
Q33. Which of the following is a function of lipid rafts?
  • A) Ion transport
  • B) Membrane rigidity only
  • C) Signaling platform concentrating signaling molecules ✓
  • D) ATP synthesis
  • E) DNA replication
Answer: C — Signaling platform Lipid rafts contain large numbers of integral and peripheral membrane proteins involved in signal transduction. (Histology)
Q34. The property of amphipathicity in phospholipids means:
  • A) They are entirely hydrophobic
  • B) They are entirely hydrophilic
  • C) They have both hydrophilic and hydrophobic regions ✓
  • D) They carry a net negative charge
  • E) They are insoluble in all solvents
Answer: C — Both hydrophilic and hydrophobic regions The lipid molecules form a lipid bilayer with an amphipathic character — it is both hydrophobic and hydrophilic. (Histology)
Q35. Cardiolipin is characteristically enriched in which membrane?
  • A) Plasma membrane
  • B) Nuclear membrane
  • C) Inner mitochondrial membrane ✓
  • D) Endoplasmic reticulum membrane
  • E) Golgi membrane
Answer: C — Inner mitochondrial membrane Cardiolipin is a phospholipid uniquely enriched in the inner mitochondrial membrane, essential for electron transport chain function.
Q36. Phosphatidylinositol bisphosphate (PIP₂) is cleaved by phospholipase C to produce:
  • A) Arachidonic acid and lysophospholipid
  • B) Inositol trisphosphate (IP₃) and diacylglycerol (DAG) ✓
  • C) Cyclic AMP and phosphate
  • D) Ceramide and sphingosine
  • E) Eicosanoids and prostaglandins
Answer: B — IP₃ and DAG PIP₂ cleavage by phospholipase C generates IP₃ and DAG — key second messengers.
Q37. Which of the following best describes "flip-flop" of membrane phospholipids?
  • A) Rapid lateral diffusion within one leaflet
  • B) Movement of a lipid from one leaflet to the other ✓
  • C) Rotation of a lipid around its axis
  • D) Formation of lipid rafts
  • E) Exocytosis of membrane vesicles
Answer: B — Movement from one leaflet to the other Flip-flop (transverse diffusion) is the movement of phospholipids between the two membrane leaflets, which is normally slow and requires flippases.
Q38. The enzyme that actively moves phosphatidylserine from the outer leaflet to the inner leaflet of the plasma membrane is called:
  • A) Scramblase
  • B) Floppase
  • C) Flippase ✓
  • D) Phospholipase A2
  • E) Sphingomyelinase
Answer: C — Flippase Flippases (aminophospholipid translocases) use ATP to move phosphatidylserine and phosphatidylethanolamine from the outer to the inner leaflet.
Q39. Which protein complex anchors the spectrin-actin cytoskeleton to the red blood cell plasma membrane?
  • A) Dystrophin-glycoprotein complex
  • B) Ankyrin-Band 3 complex ✓
  • C) Integrin-fibronectin complex
  • D) Cadherin-catenin complex
  • E) Ezrin-radixin-moesin complex
Answer: B — Ankyrin-Band 3 complex Ankyrin links spectrin to the integral membrane protein Band 3 in red blood cells.
Q40. Gap junctions are formed by which proteins?
  • A) Claudins
  • B) Occludins
  • C) Connexins ✓
  • D) Cadherins
  • E) Integrins
Answer: C — Connexins Gap junctions are composed of connexins that form channels allowing direct intercellular communication.
Q41. Tight junctions are formed by which proteins?
  • A) Connexins
  • B) Claudins and occludins ✓
  • C) Integrins
  • D) Selectins
  • E) Cadherins
Answer: B — Claudins and occludins Tight junctions (zonula occludens) are formed by claudins and occludins, sealing adjacent epithelial cells.
Q42. Membrane fluidity DECREASES with:
  • A) Increased unsaturated fatty acids
  • B) Increased temperature
  • C) Increased cholesterol at physiological temperatures ✓ (can also increase rigidity at high cholesterol)
  • D) Decreased sphingolipid content
  • E) Decreased protein-to-lipid ratio
Answer: C Cholesterol reduces membrane fluidity by filling spaces between phospholipid tails and restricting their movement at physiological temperatures.
Q43. Which of the following is NOT a function of the cell membrane?
  • A) Transport of substances
  • B) Cell recognition
  • C) Signal transduction
  • D) Protein synthesis ✓
  • E) Enzymatic activity
Answer: D — Protein synthesis Protein synthesis occurs on ribosomes (rough ER), not at the cell membrane.
Q44. Transmembrane proteins that span the membrane multiple times are said to have:
  • A) Single-pass topology
  • B) GPI anchor
  • C) Multi-pass (polytopic) topology ✓
  • D) Peripheral attachment
  • E) Lipid-anchored topology
Answer: C — Multi-pass topology Proteins like ion channels and G-protein coupled receptors span the membrane multiple times.
Q45. GPI (glycosylphosphatidylinositol)-anchored proteins are:
  • A) Transmembrane proteins with cytoplasmic domains
  • B) Peripheral proteins on the cytoplasmic face
  • C) Proteins attached to the outer leaflet via a lipid anchor ✓
  • D) Proteins synthesized in the cytosol
  • E) Proteins that form ion channels
Answer: C GPI-anchored proteins are tethered to the outer leaflet of the plasma membrane via a glycosylphosphatidylinositol anchor.
Q46. Which membrane lipid is the precursor for steroid hormones?
  • A) Phosphatidylcholine
  • B) Sphingomyelin
  • C) Cholesterol ✓
  • D) Cardiolipin
  • E) Phosphatidylserine
Answer: C — Cholesterol Cholesterol is the precursor for all steroid hormones, bile acids, and vitamin D.
Q47. The sodium-potassium ATPase pump maintains which ionic gradient?
  • A) High Na⁺ inside, high K⁺ outside
  • B) High Na⁺ outside, high K⁺ inside ✓
  • C) High Ca²⁺ inside, low Ca²⁺ outside
  • D) Equal Na⁺ and K⁺ on both sides
  • E) High Cl⁻ inside the cell
Answer: B — High Na⁺ outside, high K⁺ inside The Na⁺/K⁺-ATPase pumps 3 Na⁺ out and 2 K⁺ in per cycle, maintaining the normal ionic gradient.
Q48. Which of the following membrane proteins is responsible for active transport requiring ATP?
  • A) Ion channels
  • B) Carrier proteins (facilitators)
  • C) ATPase pumps ✓
  • D) Aquaporins
  • E) Receptor tyrosine kinases
Answer: C — ATPase pumps ATPase pumps (P-type, ABC transporters) use ATP hydrolysis for active transport against concentration gradients.
Q49. The Singer-Nicolson fluid-mosaic model was proposed in which year?
  • A) 1953
  • B) 1966
  • C) 1972 ✓
  • D) 1980
  • E) 1990
Answer: C — 1972 Singer and Nicolson proposed the fluid-mosaic model in 1972.
Q50. Which of the following best explains why red blood cells can change shape while passing through capillaries without rupturing?
  • A) High cholesterol content of their membrane
  • B) Spectrin-actin cytoskeleton providing membrane elasticity ✓
  • C) Absence of integral membrane proteins
  • D) Glycocalyx providing rigidity
  • E) High sphingolipid content
Answer: B — Spectrin-actin cytoskeleton The spectrin-actin cytoskeletal meshwork underlying the red blood cell membrane provides the elasticity and flexibility needed to traverse narrow capillaries.

Section B: Apoptosis (Q51–100)

Q51. Apoptosis is best defined as:
  • A) Passive cell death due to toxic injury
  • B) Cell death by membrane rupture and inflammation
  • C) A regulated mechanism of cell death that eliminates unwanted cells with minimal host reaction ✓
  • D) Cell death due to ischemia
  • E) Necrotic death due to complement activation
Answer: C Apoptosis is a regulated mechanism of cell death that serves to eliminate unwanted and irreparably damaged cells, with the least possible host reaction. (Robbins)
Q52. Which enzymes are primarily responsible for the degradation of proteins and DNA during apoptosis?
  • A) Lysosomal hydrolases
  • B) Caspases ✓
  • C) Phospholipases
  • D) Matrix metalloproteinases
  • E) Telomerases
Answer: B — Caspases Apoptosis is characterized by enzymatic degradation of proteins and DNA, initiated by caspases. (Robbins)
Q53. The two major pathways of apoptosis are:
  • A) Lysosomal and proteasomal pathways
  • B) Mitochondrial (intrinsic) and death receptor (extrinsic) pathways ✓
  • C) Necrotic and autophagic pathways
  • D) Caspase-dependent and caspase-independent pathways
  • E) Nuclear and cytoplasmic pathways
Answer: B Apoptosis is initiated by two major pathways: the mitochondrial (intrinsic) pathway and the death receptor (extrinsic) pathway. (Robbins)
Q54. The intrinsic (mitochondrial) pathway of apoptosis is triggered by all of the following EXCEPT:
  • A) Loss of survival signals
  • B) DNA damage
  • C) Accumulation of misfolded proteins (ER stress)
  • D) Engagement of Fas receptor by FasL ✓
  • E) Radiation
Answer: D — Engagement of Fas receptor by FasL Fas/FasL engagement activates the extrinsic (death receptor) pathway, not the intrinsic pathway. (Robbins)
Q55. In the mitochondrial pathway of apoptosis, which pro-apoptotic protein leaks from the mitochondria into the cytoplasm?
  • A) BCL-XL
  • B) MCL1
  • C) Cytochrome c ✓
  • D) XIAP
  • E) Survivin
Answer: C — Cytochrome c Cytochrome c released into the cytoplasm initiates the suicide program of apoptosis. (Robbins)
Q56. The BCL2 family of proteins regulates apoptosis by controlling:
  • A) Caspase-8 activation directly
  • B) Death receptor expression
  • C) The integrity of the outer mitochondrial membrane ✓
  • D) Nuclear chromatin condensation
  • E) Phagocytosis of apoptotic bodies
Answer: C The release of pro-apoptotic proteins such as cytochrome c is determined by the integrity of the outer mitochondrial membrane, which is tightly controlled by the BCL2 family. (Robbins)
Q57. Which of the following are ANTI-apoptotic members of the BCL2 family?
  • A) BAX and BAK
  • B) BIM, BID, and Noxa
  • C) BCL2, BCL-XL, and MCL1 ✓
  • D) PUMA and BAD
  • E) Caspase-9 and APAF-1
Answer: C — BCL2, BCL-XL, MCL1 Anti-apoptotic members include BCL2, BCL-XL, and MCL1; they possess four BH domains (BH1–4). (Robbins)
Q58. The pro-apoptotic members BAX and BAK contain which BH domains?
  • A) BH1 only
  • B) BH1–4
  • C) BH1–3 ✓
  • D) BH3 only
  • E) BH2–4
Answer: C — BH1–3 BAX and BAK are the two prototypic pro-apoptotic members; they contain the first three BH domains (BH1–3). (Robbins)
Q59. BH3-only proteins such as BIM, BID, and Noxa are referred to as:
  • A) Anti-apoptotic regulators
  • B) Execution caspases
  • C) Regulated apoptosis initiators ✓
  • D) Death receptor ligands
  • E) Apoptosome components
Answer: C — Regulated apoptosis initiators BH3-only proteins contain only the third BH domain; their activity is modulated by sensors of cellular stress and damage. (Robbins)
Q60. Once cytochrome c is released into the cytosol, it binds to which protein to form the apoptosome?
  • A) Caspase-3
  • B) XIAP
  • C) APAF-1 ✓
  • D) BCL2
  • E) FADD
Answer: C — APAF-1 Cytochrome c binds to APAF-1 (apoptosis-activating factor-1), forming a multimeric structure called the apoptosome. (Robbins)
Q61. The apoptosome activates which initiator caspase?
  • A) Caspase-1
  • B) Caspase-8
  • C) Caspase-10
  • D) Caspase-9 ✓
  • E) Caspase-3
Answer: D — Caspase-9 The apoptosome binds to caspase-9, the critical initiator caspase of the mitochondrial pathway. (Robbins)
Q62. In the extrinsic (death receptor) pathway, the initiator caspase activated is:
  • A) Caspase-9
  • B) Caspase-3
  • C) Caspase-8 ✓
  • D) Caspase-1
  • E) Caspase-12
Answer: C — Caspase-8 The extrinsic pathway uses two related initiator caspases, caspase-8 and caspase-10. (Janeway's Immunobiology)
Q63. Death receptors belong to which protein superfamily?
  • A) Interleukin receptor family
  • B) TNF receptor family ✓
  • C) Integrin family
  • D) Toll-like receptor family
  • E) Tyrosine kinase receptor family
Answer: B — TNF receptor family The death receptor pathway is initiated by engagement of death receptors, which are members of the TNF receptor family. (Robbins)
Q64. The extrinsic apoptotic pathway is initiated by:
  • A) DNA double-strand breaks
  • B) ER stress
  • C) Binding of death ligands (e.g., FasL, TNF) to death receptors ✓
  • D) Mitochondrial membrane depolarization
  • E) Growth factor withdrawal
Answer: C The extrinsic pathway is initiated by engagement of death receptors by ligands, which can be soluble or cell surface-expressed. (Robbins)
Q65. The effector caspase that mediates the final execution phase of apoptosis in both pathways is:
  • A) Caspase-9
  • B) Caspase-8
  • C) Caspase-3 ✓
  • D) Caspase-1
  • E) Caspase-12
Answer: C — Caspase-3 Active caspase-9 triggers a cascade by cleaving and activating other pro-caspases such as caspase-3, which mediate the execution phase. (Robbins)
Q66. In apoptosis, cells break up into membrane-enclosed fragments called:
  • A) Necrotic bodies
  • B) Apoptotic bodies ✓
  • C) Autophagosomes
  • D) Phagolysosomes
  • E) Oncotic blebs
Answer: B — Apoptotic bodies The formation of apoptotic bodies breaks cells up into "bite-sized" fragments that are edible for phagocytes. (Robbins)
Q67. In apoptotic cells, phosphatidylserine moves from the inner to the outer leaflet of the plasma membrane. This process is mediated by:
  • A) Flippase activation
  • B) Flippase inhibition and scramblase activation ✓
  • C) Caspase-9 directly
  • D) BCL-XL
  • E) APAF-1
Answer: B — Scramblase activation In apoptotic cells, phosphatidylserine "flips" out and is expressed on the outer layer — mediated by scramblases that randomize lipid distribution.
Q68. Externalized phosphatidylserine on apoptotic cells serves as:
  • A) A "don't eat me" signal
  • B) An "eat me" signal recognized by macrophage receptors ✓
  • C) A trigger for complement activation only
  • D) An inflammatory mediator
  • E) A substrate for caspase-3
Answer: B Phosphatidylserine expressed on the outer layer is recognized by several macrophage receptors as an "eat me" signal. (Robbins)
Q69. The phagocytosis of apoptotic cells by macrophages is called:
  • A) Phagoptosis
  • B) Frustrated phagocytosis
  • C) Efferocytosis ✓
  • D) Autophagy
  • E) Transcytosis
Answer: C — Efferocytosis The process of apoptotic phagocytosis is called efferocytosis; it is so efficient that dead cells disappear, often within minutes. (Robbins)
Q70. BCL2 was originally identified as a gene overexpressed due to chromosomal translocation in:
  • A) T-cell lymphoma
  • B) Chronic myelogenous leukemia
  • C) Certain B-cell lymphomas ✓
  • D) Acute lymphoblastic leukemia
  • E) Multiple myeloma
Answer: C — Certain B-cell lymphomas BCL2, a gene frequently overexpressed due to chromosomal translocations, was identified in certain B cell lymphomas. (Robbins)
Q71. The translocation t(14;18) in follicular lymphoma results in overexpression of which anti-apoptotic protein?
  • A) MCL1
  • B) BCL-XL
  • C) BCL2 ✓
  • D) Survivin
  • E) XIAP
Answer: C — BCL2 t(14;18) juxtaposes BCL2 to the immunoglobulin heavy chain promoter, causing BCL2 overexpression and inhibited apoptosis.
Q72. Anti-apoptotic BCL2 family members reside in which cellular compartments?
  • A) Nucleus and cytosol
  • B) Outer mitochondrial membrane, cytosol, and ER membranes ✓
  • C) Inner mitochondrial membrane only
  • D) Lysosomal membrane
  • E) Plasma membrane only
Answer: B BCL2, BCL-XL, and MCL1 reside in the outer mitochondrial membrane as well as in the cytosol and ER membranes. (Robbins)
Q73. Smac/DIABLO proteins released from mitochondria during apoptosis function by:
  • A) Activating BCL2
  • B) Inhibiting caspase-9 directly
  • C) Neutralizing inhibitors of apoptosis (IAPs) ✓
  • D) Activating the extrinsic pathway
  • E) Phosphorylating BAX
Answer: C — Neutralizing IAPs Smac/DIABLO neutralize inhibitor-of-apoptosis proteins (IAPs), thereby allowing caspase activation to proceed.
Q74. Which caspases are classified as "initiator caspases"?
  • A) Caspase-3 and caspase-7
  • B) Caspase-8, caspase-9, and caspase-10 ✓
  • C) Caspase-1 and caspase-5
  • D) Caspase-3 and caspase-6
  • E) Caspase-12 only
Answer: B — Caspase-8, -9, -10 Initiator caspases promote apoptosis by cleaving and activating other caspases; initiators include caspase-8, -9, and -10. (Janeway's)
Q75. DISC (Death-Inducing Signaling Complex) is formed in which pathway of apoptosis?
  • A) Intrinsic (mitochondrial) pathway
  • B) Extrinsic (death receptor) pathway ✓
  • C) Lysosomal pathway
  • D) p53-dependent pathway
  • E) Autophagic pathway
Answer: B — Extrinsic pathway DISC forms at the death receptor upon ligand binding, recruiting FADD and procaspase-8.
Q76. FADD (Fas-Associated Death Domain) is a key adaptor protein in which pathway?
  • A) Intrinsic pathway
  • B) Extrinsic (death receptor) pathway ✓
  • C) Necroptosis pathway
  • D) Autophagy pathway
  • E) p53 pathway
Answer: B — Extrinsic pathway The extrinsic pathway involves recruitment of Fas-associated death domain protein (FADD) following death receptor engagement. (Schwartz's Surgery)
Q77. p53 promotes apoptosis primarily by:
  • A) Directly activating caspase-3
  • B) Transcriptionally upregulating pro-apoptotic BH3-only proteins (e.g., PUMA, Noxa) ✓
  • C) Inhibiting BCL2
  • D) Activating scramblase
  • E) Cleaving APAF-1
Answer: B p53 activates transcription of pro-apoptotic BH3-only proteins including PUMA and Noxa in response to DNA damage.
Q78. Which of the following distinguishes apoptosis from necrosis?
  • A) Apoptosis causes inflammation; necrosis does not
  • B) Apoptosis leads to cell swelling; necrosis leads to cell shrinkage
  • C) Apoptosis is energy (ATP)-dependent; necrosis is passive ✓
  • D) Apoptosis involves lysosomal rupture; necrosis does not
  • E) Apoptosis is always pathological; necrosis can be physiological
Answer: C Apoptosis is a regulated, energy-requiring process; necrosis is a passive response to overwhelming injury.
Q79. Morphological features of apoptosis include all of the following EXCEPT:
  • A) Cell shrinkage
  • B) Chromatin condensation (pyknosis)
  • C) Nuclear fragmentation (karyorrhexis)
  • D) Cell swelling and membrane rupture ✓
  • E) Formation of apoptotic bodies
Answer: D — Cell swelling and membrane rupture Apoptosis causes cell shrinkage and condensation; cell swelling and membrane rupture are features of necrosis.
Q80. The ladder pattern seen on agarose gel electrophoresis of DNA from apoptotic cells is due to:
  • A) Random DNA degradation
  • B) Internucleosomal DNA cleavage at ~180 bp intervals ✓
  • C) Oxidative DNA damage
  • D) Telomere shortening
  • E) Mitochondrial DNA release
Answer: B — Internucleosomal DNA cleavage Caspase-activated DNase (CAD) cleaves DNA at internucleosomal linker regions (~180 bp), producing the characteristic ladder pattern.
Q81. Necroptosis differs from apoptosis in that it:
  • A) Is caspase-dependent
  • B) Does not involve cell death signaling
  • C) Is morphologically similar to necrosis but mechanistically programmed ✓
  • D) Produces apoptotic bodies
  • E) Is anti-inflammatory
Answer: C Necroptosis resembles necrosis morphologically but is triggered by signal transduction pathways, hence called "programmed necrosis." (Robbins)
Q82. Growth factors promote cell survival by:
  • A) Directly activating caspase-9
  • B) Stimulating production of anti-apoptotic proteins like BCL2 ✓
  • C) Inhibiting APAF-1 assembly
  • D) Downregulating BH3-only proteins
  • E) Activating the extrinsic pathway
Answer: B Growth factors and survival signals stimulate the production of anti-apoptotic proteins such as BCL2, protecting cells from apoptosis. (Robbins)
Q83. Efferocytosis (apoptotic cell clearance) by macrophages results in:
  • A) Release of pro-inflammatory cytokines
  • B) Necrosis of the macrophage
  • C) Reduction of pro-inflammatory cytokine production ✓
  • D) Activation of the adaptive immune response
  • E) Complement deposition
Answer: C Production of proinflammatory cytokines is reduced in macrophages that have ingested apoptotic cells, limiting inflammatory reactions. (Robbins)
Q84. The protein C1q, which coats apoptotic cells, functions as:
  • A) An anti-phagocytic signal
  • B) An opsonin facilitating recognition by phagocytes ✓
  • C) A caspase inhibitor
  • D) A membrane stabilizer
  • E) A BCL2 activator
Answer: B Apoptotic bodies may become coated with natural antibodies and complement proteins notably C1q, recognized by phagocyte receptors. (Robbins)
Q85. In cytotoxic T lymphocyte (CTL)-mediated killing, apoptosis of target cells is induced by:
  • A) Only the intrinsic pathway
  • B) Either the extrinsic or intrinsic pathway ✓
  • C) Only the extrinsic pathway via perforin
  • D) Complement activation
  • E) Autophagy
Answer: B — Either extrinsic or intrinsic CTL-induced apoptosis can occur by either the extrinsic pathway (death receptors) or the intrinsic pathway. (Janeway's)
Q86. Granzyme B, released by cytotoxic T cells, causes target cell apoptosis by:
  • A) Directly rupturing the mitochondrial membrane
  • B) Activating BCL2
  • C) Cleaving and activating procaspases ✓
  • D) Inhibiting APAF-1
  • E) Binding to death receptors
Answer: C Granzyme B enters target cells through perforin pores and cleaves/activates procaspases, triggering apoptosis.
Q87. Physiological examples of apoptosis include all of the following EXCEPT:
  • A) Elimination of self-reactive lymphocytes
  • B) Regression of the tadpole tail during metamorphosis
  • C) Formation of fingers during embryogenesis (interdigital web removal)
  • D) Hepatocyte death after ischemia ✓
  • E) Endometrial shedding during menstruation
Answer: D — Hepatocyte death after ischemia Ischemic hepatocyte death is necrosis; all others represent physiological (programmed) apoptosis.
Q88. TP53 (p53) is called "guardian of the genome" because it:
  • A) Directly repairs DNA
  • B) Inhibits cell cycle progression and induces apoptosis in response to DNA damage ✓
  • C) Activates BCL2 expression
  • D) Promotes cell proliferation
  • E) Forms the apoptosome
Answer: B p53 halts the cell cycle and, if damage is irreparable, initiates apoptosis, preventing propagation of genetic errors.
Q89. Which caspase is the key initiator in the intrinsic (mitochondrial) pathway?
  • A) Caspase-1
  • B) Caspase-3
  • C) Caspase-8
  • D) Caspase-9 ✓
  • E) Caspase-10
Answer: D — Caspase-9 The apoptosome binds to caspase-9, the critical initiator caspase of the mitochondrial pathway, and promotes its autocatalytic cleavage. (Robbins)
Q90. BAX and BAK exert their pro-apoptotic function by:
  • A) Binding and inhibiting BCL2
  • B) Oligomerizing in the outer mitochondrial membrane to increase its permeability ✓
  • C) Directly activating caspase-3
  • D) Promoting APAF-1 degradation
  • E) Inhibiting scramblase
Answer: B On activation, BAX/BAK oligomerize within the outer mitochondrial membrane and enhance its permeability, allowing cytochrome c leakage. (Robbins)
Q91. Which of the following is a key feature that distinguishes apoptosis from autophagy?
  • A) Apoptosis involves lysosomal digestion; autophagy does not
  • B) Autophagy sequesters organelles in double-membrane vesicles; apoptosis does not ✓
  • C) Apoptosis only occurs in cancer cells
  • D) Autophagy is always pro-death
  • E) Both require caspase activation equally
Answer: B Autophagy involves double-membrane autophagosomes engulfing organelles/proteins; apoptosis involves caspase-mediated cell dismantling into apoptotic bodies.
Q92. Anoikis is a specific type of apoptosis triggered by:
  • A) DNA double-strand breaks
  • B) Growth factor withdrawal
  • C) Loss of integrin-mediated cell-matrix attachment ✓
  • D) Viral infection
  • E) Mitochondrial ROS accumulation
Answer: C — Loss of cell-matrix attachment Anoikis is apoptosis induced when cells detach from the extracellular matrix, preventing metastasis of normal epithelial cells.
Q93. Survivin and XIAP are examples of:
  • A) Pro-apoptotic caspases
  • B) BH3-only proteins
  • C) Inhibitors of apoptosis proteins (IAPs) ✓
  • D) Death receptor ligands
  • E) BCL2-like anti-apoptotic proteins
Answer: C — IAPs Inhibitor of apoptosis proteins (IAPs) including survivin and XIAP block caspase activity; they are neutralized by Smac/DIABLO.
Q94. Pyroptosis is a form of programmed cell death that is:
  • A) Non-inflammatory and mediated by caspase-9
  • B) Highly inflammatory and mediated by caspase-1 or caspase-11 ✓
  • C) Identical to apoptosis morphologically
  • D) Mediated by RIPK3
  • E) ATP-dependent and non-inflammatory
Answer: B Pyroptosis is inflammatory cell death mediated by caspase-1 (and caspase-11/4/5), forming gasdermin pores and releasing IL-1β and IL-18.
Q95. The "ladder pattern" of DNA fragmentation on gel electrophoresis is characteristic of:
  • A) Necrosis
  • B) Autophagy
  • C) Apoptosis ✓
  • D) Necroptosis
  • E) Ferroptosis
Answer: C — Apoptosis Internucleosomal DNA cleavage at ~180 bp multiples produces the characteristic "ladder" on gel electrophoresis, a hallmark of apoptosis.
Q96. Ferroptosis is a recently described form of cell death characterized by:
  • A) Caspase activation and apoptotic body formation
  • B) Dependence on iron and accumulation of lipid peroxides ✓
  • C) Inflammatory cytokine release via gasdermin pores
  • D) RIPK3 activation and plasma membrane rupture
  • E) Bcl-2-dependent mitochondrial permeability
Answer: B Ferroptosis is an iron-dependent form of cell death characterized by accumulation of lipid peroxides, distinct from apoptosis and necrosis.
Q97. Cytochrome c in the mitochondrial intermembrane space normally functions as:
  • A) A substrate of caspase-9
  • B) An anti-apoptotic protein
  • C) An electron carrier in the respiratory chain ✓
  • D) A component of the apoptosome
  • E) A BH3-only protein
Answer: C — Electron carrier Cytochrome c is essential for producing ATP (electron transport chain); when released into the cytoplasm, it initiates apoptosis. (Robbins)
Q98. Anti-apoptotic BCL2 proteins prevent cytochrome c release by:
  • A) Directly activating caspase inhibitors
  • B) Keeping the outer mitochondrial membrane impermeable ✓
  • C) Sequestering APAF-1
  • D) Phosphorylating BAX
  • E) Activating RIPK1
Answer: B By keeping the mitochondrial outer membrane impermeable, BCL2/BCL-XL/MCL1 prevent leakage of cytochrome c and other death-inducing proteins. (Robbins)
Q99. ER stress-induced apoptosis occurs primarily through which pathway?
  • A) Extrinsic (death receptor) pathway
  • B) Intrinsic (mitochondrial) pathway via BH3-only proteins ✓
  • C) DISC formation
  • D) Granzyme B activation
  • E) Complement-mediated lysis
Answer: B ER stress due to misfolded proteins upregulates BH3-only proteins, activating the intrinsic mitochondrial pathway of apoptosis. (Robbins)
Q100. In which of the following conditions is defective apoptosis a key pathogenic mechanism?
  • A) Myocardial infarction
  • B) Stroke
  • C) Follicular lymphoma (BCL2 overexpression) ✓
  • D) Diabetes mellitus type 1
  • E) Rheumatoid arthritis
Answer: C — Follicular lymphoma BCL2 overexpression due to t(14;18) translocation in follicular lymphoma is the classic example of defective apoptosis driving tumor development. (Robbins)

Quick Reference Summary

TopicKey Facts
Membrane composition55% protein, 25% phospholipid, 13% cholesterol, 4% other lipids, 3% carbohydrate
Membrane thickness7.5–10 nm
Main membrane lipidsPhospholipids > Sphingolipids > Cholesterol
Cholesterol roleControls fluidity and permeability
Fluid-mosaic modelSinger & Nicolson, 1972
PhosphatidylserineInner leaflet normally; outer leaflet in apoptosis ("eat me" signal)
Apoptosis triggers (intrinsic)DNA damage, growth factor withdrawal, ER stress
Apoptosis triggers (extrinsic)FasL/Fas, TNF/TNFR engagement
Anti-apoptotic BCL2 membersBCL2, BCL-XL, MCL1 (BH1–4)
Pro-apoptotic BCL2 membersBAX, BAK (BH1–3); BH3-only: BIM, BID, PUMA, Noxa, BAD
Intrinsic pathway caspaseCaspase-9 (initiator) → Caspase-3 (effector)
Extrinsic pathway caspaseCaspase-8 (initiator) → Caspase-3 (effector)
ApoptosomeCytochrome c + APAF-1 + Caspase-9
EfferocytosisPhagocytosis of apoptotic bodies by macrophages
Follicular lymphomat(14;18) → BCL2 overexpression → impaired apoptosis
Sources: Robbins & Cotran Pathologic Basis of Disease; Guyton & Hall Textbook of Medical Physiology; Histology: A Text and Atlas (Pawlina); Junqueira's Basic Histology; Janeway's Immunobiology 10e.
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