Question 1

Which of the following best explains why induced pluripotent stem cells (iPSCs) are considered pluripotent but not totipotent?

Accepted Answer

iPSCs are derived from reprogrammed somatic cells and can differentiate into all body cell types except placental tissue.

Question 2

A patient with Marfan syndrome has a mutation in the FBN1 gene. Which of the following mechanisms contributes to the aortic pathology observed in this disease?

Accepted Answer

Defective fibrillin fails to sequester TGF-β, resulting in excess TGF-β signaling and abnormal connective tissue remodeling.

Question 3

Which junction is primarily responsible for sealing the paracellular space between epithelial cells, and what is the consequence of its dysfunction?

Accepted Answer

Tight junction; loss results in compromised barrier function and increased paracellular permeability.

Question 4

A drug that disrupts lipid rafts in the plasma membrane would most likely impair which cellular function?

Accepted Answer

Signal transduction by concentrating receptors and associated proteins.

Question 5

Which cytoskeletal element is non-polar, requires no energy for assembly, and provides mechanical strength to cells?

Accepted Answer

Intermediate filaments

Question 6

A patient presents with chronic respiratory infections, situs inversus, and infertility. Which cytoskeletal defect is most likely responsible?

Accepted Answer

Deficiency of axonemal dynein arms in motile cilia, impairing ciliary movement.

Question 7

Which of the following best describes the mechanism of action of Taxol (paclitaxel) in cancer therapy?

Accepted Answer

Taxol stabilizes assembled microtubules, blocking disassembly and causing mitotic arrest.

Question 8

A mutation in the gene encoding the β2 integrin subunit would most directly impair which immune cell function?

Accepted Answer

Firm adhesion of leukocytes to the endothelium during inflammation.

Question 9

Which of the following statements about chromatin states is correct?

Accepted Answer

Euchromatin is dispersed, light-staining, and transcriptionally active.

Question 10

A cell with a mutation in the POLE exonuclease domain would most likely exhibit which phenotype?

Accepted Answer

Increased mutation rate due to loss of 3′→5′ exonuclease proofreading activity.

Question 11

Which of the following best explains the clinical use of isotonic saline in intravenous therapy?

Accepted Answer

Isotonic saline matches extracellular fluid osmolality, preventing net water movement across cell membranes.

Question 12

A patient with I-cell disease has normal lysosomal hydrolase enzymes, but they are found in the extracellular space. Which step in protein processing is defective?

Accepted Answer

Mannose-6-phosphate tagging in the Golgi apparatus.

Question 13

Which of the following is a direct trigger for the intrinsic (mitochondrial) pathway of apoptosis?

Accepted Answer

Release of cytochrome c from the mitochondrial intermembrane space into the cytosol.

Question 14

Which of the following equations correctly represents the calculation of osmolality ($$O) $$for a solution containing $$n$$ solute particles per kilogram of solvent?

Accepted Answer

$$O = \frac{n}{	ext{kg solvent}}$$

Question 15

A cell undergoing apoptosis externalizes phosphatidylserine (PS) to the outer leaflet of its plasma membrane. Which protein maintains this asymmetry under normal conditions?

Accepted Answer

Flippase

Question 16

Which enzyme is responsible for relieving supercoiling ahead of the replication fork during DNA replication?

Accepted Answer

Topoisomerase

Question 17

A patient with a mutation in BRCA1/2 is treated with a PARP inhibitor. What is the underlying principle that explains selective tumor cell death?

Accepted Answer

Synthetic lethality: loss of both homologous recombination and base excision repair leaves no viable DNA repair pathway.

Question 18

Which RNA polymerase is responsible for transcribing all protein-coding genes in eukaryotic cells, and what unique feature does it possess?

Accepted Answer

RNA Pol II; possesses a unique C-terminal domain (CTD) that docks processing machinery.

Question 19

Which modification is most likely to open chromatin and increase transcriptional accessibility?

Accepted Answer

Histone acetylation by HAT enzymes.

Question 20

A mutation in the GU/AG consensus sequence at an intron boundary would most likely result in which outcome?

Accepted Answer

Aberrant splicing, leading to exon skipping or intron retention.

Cell Biology Exam 1: High-Yield Study Guide (Chapters 1–8)

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