BIO 415 CELL BIOLOGY FINAL EXAM
Organelle Function Membrane Transport Signal Transduction
Cytoskeleton and Cell Cycle Questions and Answers Verified
Solutions 2026 2027
1. Which organelle contains acid hydrolases maintained at a low pH by ATP-driven
proton pumps to break down cellular waste and macromolecules?
A. Peroxisome
B. Lysosome
C. Golgi apparatus
D. Endoplasmic reticulum
Rationale: Lysosomes serve as the primary digestive compartments in animal cells. Proton pumps
maintain their internal environment at roughly pH 4.5 to 5.0, optimal for acid hydrolases to function without
damaging the rest of the cell.
2. What phospholipid asymmetry component is exposed on the outer leaflet of the
plasma membrane as an early marker during apoptosis?
A. Phosphatidylcholine
B. Phosphatidylserine
C. Sphingomyelin
D. Phosphatidylinositol
Rationale: Under normal conditions, flippases keep phosphatidylserine restricted to the inner cytosolic
leaflet. During programmed cell death, scramblases expose it on the extracellular surface to attract
phagocytic cells.
3. Which motor protein moves cargo along microtubules toward the minus end, typically
directed toward the cell center or centrosome?
A. Cytoplasmic Dynein
B. Kinesin-1
C. Myosin V
D. Kinesin-5
Rationale: Dynein motors travel toward microtubule minus ends located near centrosomes. Most kinesins
, drive retrograde transport toward the plus ends near the cell perimeter.
4. During signal transduction via G protein-coupled receptors (GPCRs), what exchange
occurs to activate the heterotrimeric G protein alpha subunit?
A. ATP is hydrolyzed to ADP
B. Bound GDP is replaced by GTP
C. Bound GTP is hydrolyzed to GDP
D. AMP is phosphorylated to ATP
Rationale: Ligand binding alters GPCR conformation so it acts as a guanine nucleotide exchange factor
(GEF), causing the G alpha subunit to release GDP and bind a fresh molecule of GTP.
5. What cyclin-CDK complex activity triggers the transition from G2 phase into Mitosis
during the eukaryotic cell cycle?
A. Cyclin D - CDK4/6
B. Cyclin E - CDK2
C. Cyclin B - CDK1
D. Cyclin A - CDK2
Rationale: The complex of Cyclin B and CDK1 (historically called Maturation-Promoting Factor or MPF)
phosphorylates nuclear lamins and histones to drive the cell past the G2 checkpoint into mitosis.
6. Which cell junction protein forms gated intercellular channels that allow small water-
soluble ions and signaling molecules to pass directly between adjacent animal cells?
A. Cadherin
B. Connexin
C. Occludin
D. Integrin
Rationale: Six connexin protein subunits assemble to form a connexon channel. Two aligned connexons
on neighboring cells form a gap junction, enabling electrical and metabolic coupling.
7. Which cytoskeletal filament is composed of unbranched polymers of actin and
facilitates cell locomotion, cytokinesis, and muscle contraction?
A. Microfilaments
Organelle Function Membrane Transport Signal Transduction
Cytoskeleton and Cell Cycle Questions and Answers Verified
Solutions 2026 2027
1. Which organelle contains acid hydrolases maintained at a low pH by ATP-driven
proton pumps to break down cellular waste and macromolecules?
A. Peroxisome
B. Lysosome
C. Golgi apparatus
D. Endoplasmic reticulum
Rationale: Lysosomes serve as the primary digestive compartments in animal cells. Proton pumps
maintain their internal environment at roughly pH 4.5 to 5.0, optimal for acid hydrolases to function without
damaging the rest of the cell.
2. What phospholipid asymmetry component is exposed on the outer leaflet of the
plasma membrane as an early marker during apoptosis?
A. Phosphatidylcholine
B. Phosphatidylserine
C. Sphingomyelin
D. Phosphatidylinositol
Rationale: Under normal conditions, flippases keep phosphatidylserine restricted to the inner cytosolic
leaflet. During programmed cell death, scramblases expose it on the extracellular surface to attract
phagocytic cells.
3. Which motor protein moves cargo along microtubules toward the minus end, typically
directed toward the cell center or centrosome?
A. Cytoplasmic Dynein
B. Kinesin-1
C. Myosin V
D. Kinesin-5
Rationale: Dynein motors travel toward microtubule minus ends located near centrosomes. Most kinesins
, drive retrograde transport toward the plus ends near the cell perimeter.
4. During signal transduction via G protein-coupled receptors (GPCRs), what exchange
occurs to activate the heterotrimeric G protein alpha subunit?
A. ATP is hydrolyzed to ADP
B. Bound GDP is replaced by GTP
C. Bound GTP is hydrolyzed to GDP
D. AMP is phosphorylated to ATP
Rationale: Ligand binding alters GPCR conformation so it acts as a guanine nucleotide exchange factor
(GEF), causing the G alpha subunit to release GDP and bind a fresh molecule of GTP.
5. What cyclin-CDK complex activity triggers the transition from G2 phase into Mitosis
during the eukaryotic cell cycle?
A. Cyclin D - CDK4/6
B. Cyclin E - CDK2
C. Cyclin B - CDK1
D. Cyclin A - CDK2
Rationale: The complex of Cyclin B and CDK1 (historically called Maturation-Promoting Factor or MPF)
phosphorylates nuclear lamins and histones to drive the cell past the G2 checkpoint into mitosis.
6. Which cell junction protein forms gated intercellular channels that allow small water-
soluble ions and signaling molecules to pass directly between adjacent animal cells?
A. Cadherin
B. Connexin
C. Occludin
D. Integrin
Rationale: Six connexin protein subunits assemble to form a connexon channel. Two aligned connexons
on neighboring cells form a gap junction, enabling electrical and metabolic coupling.
7. Which cytoskeletal filament is composed of unbranched polymers of actin and
facilitates cell locomotion, cytokinesis, and muscle contraction?
A. Microfilaments
