Cellular Physiology — MCQs

Cellular Physiology Indian Medical PG Practice Questions and MCQs

Question 341: Barr body is absent in which individuals?

A. Turner (Correct Answer)
B. Super female
C. Klinefelter
D. None of the above

Explanation: ***Turner*** - Individuals with **Turner syndrome (45,X)** have only one X chromosome and therefore no Barr bodies, as Barr bodies form from extra X chromosomes [1]. - This condition results in various clinical features including **short stature** and **gonadal dysgenesis** [1]. *Kleinfelter* - **Klinefelter syndrome (47, XXY)** typically presents with one or more Barr bodies due to the presence of an additional X chromosome [1]. - Affected individuals usually exhibit **hypogonadism** and **gynecomastia** [1]. *None of the above* - This option suggests that all listed conditions have Barr bodies, which is incorrect since Turner syndrome does not. - Hence, it fails to identify the true condition characterized by the **absence of Barr bodies**. *Super female* - Super female refers to individuals with **47, XXX** karyotype, who have one Barr body due to the two extra X chromosomes. - They often present with normal female characteristics, thus having Barr bodies. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 173-177.

Question 342: Some cells secrete chemicals into the extracellular fluid that act on cells in the same tissue. Which of the following refers to this type of regulation?

A. Neural
B. Endocrine
C. Neuroendocrine
D. Paracrine (Correct Answer)

Explanation: ***Paracrine*** - **Paracrine signaling** involves chemical messengers, or **paracrine factors**, that act on **neighboring cells** within the **same tissue** without entering the bloodstream. - This type of regulation is crucial for local communication and coordination, such as in wound healing or immune responses. *Neural* - **Neural regulation** involves communication via **neurons** that transmit **electrical signals** (action potentials) and release **neurotransmitters** at synapses. - Neurotransmitters act on target cells, which can be distant from the neuron, for rapid and precise responses throughout the body. *Endocrine* - **Endocrine regulation** involves glands that secrete **hormones** directly into the **bloodstream**, which then travel to distant target cells in other tissues or organs. - This form of signaling leads to widespread and long-lasting effects, such as growth regulation or metabolic control. *Neuroendocrine* - **Neuroendocrine regulation** is a hybrid system where specialized **neurons** (neurosecretory cells) release **hormones** into the **bloodstream**, rather than releasing neurotransmitters into a synapse. - An example is the hypothalamus secreting ADH and oxytocin, which act on distant target organs.

Question 343: Glucose is principally absorbed by which mechanism?

A. Passive diffusion
B. Facilitated diffusion
C. Active transport
D. Secondary active transport (Correct Answer)

Explanation: ***Secondary active transport*** - **Glucose** is absorbed from the intestinal lumen into enterocytes primarily via the **sodium-glucose co-transporter 1 (SGLT1)**, which is a form of secondary active transport. - This process utilizes the electrochemical gradient of **sodium ions (Na+)** established by the Na+/K+-ATPase pump, indirectly requiring ATP. *Passive diffusion* - This mechanism involves the movement of substances down their **concentration gradient** without the help of membrane proteins or energy. - While some very small, lipid-soluble molecules can use passive diffusion, **glucose** is a larger, water-soluble molecule and cannot efficiently cross the cell membrane this way. *Facilitated diffusion* - This process involves the movement of substances down their **concentration gradient** with the help of **carrier proteins** (e.g., GLUT transporters), but it does not directly require ATP. - While glucose can exit enterocytes into the bloodstream via GLUT2 through facilitated diffusion, its primary absorption from the intestinal lumen is not by this mechanism. *Active transport* - **Primary active transport** directly uses ATP to move substances against their concentration gradient (e.g., Na+/K+-ATPase pump). - While secondary active transport (which glucose uses) is a type of active transport, stating "active transport" alone is too general and doesn't specify the exact mechanism for **glucose absorption** from the lumen.

Question 344: Which adhesion molecule is involved in morphogenesis?

A. Osteopontin
B. Osteonectin SPARC
C. Tenascin (Correct Answer)
D. Thrombospondin

Explanation: ***Tenascin*** - **Tenascin** is an extracellular matrix glycoprotein that plays a crucial role in various developmental processes, including **morphogenesis**. - It influences cell adhesion, migration, and differentiation, which are all fundamental to the proper formation of tissues and organs during development. *Osteopontin* - **Osteopontin** is primarily involved in bone mineralization, cell adhesion, and immune responses. - While it has adhesive properties, its main role is not central to the broad process of **morphogenesis**. *Osteonectin SPARC* - **Osteonectin (SPARC)** is a matricellular protein involved in tissue remodeling, cell proliferation, and angiogenesis. - While important in various biological processes, it is not primarily recognized as a key player in the direct adhesive mechanisms driving **morphogenesis**. *Thrombospondin* - **Thrombospondin** is a family of matricellular proteins involved in angiogenesis, inflammation, and wound healing. - Its adhesive properties are more focused on platelet aggregation and cell-matrix interactions in tissue repair rather than the orchestrating events of **morphogenesis**.

Question 345: What is the second messenger responsible for smooth muscle relaxation mediated by nitric oxide (NO)?

A. Calcium
B. Cyclic AMP
C. Cyclic GMP (Correct Answer)
D. Magnesium

Explanation: ***Cyclic GMP*** - **Nitric oxide (NO)** activates **guanylyl cyclase**, an enzyme that converts **GTP to cGMP**. - Elevated **cGMP** levels activate **protein kinase G (PKG)**, leading to smooth muscle relaxation through various mechanisms, including reduced intracellular calcium and altered sensitivity of contractile proteins. *Calcium* - **Calcium** is primarily a key second messenger for **smooth muscle contraction**, not relaxation. - An increase in intracellular **calcium** promotes the binding of **calcium to calmodulin**, activating myosin light chain kinase and leading to contraction. *Cyclic AMP* - While **cyclic AMP (cAMP)** can cause smooth muscle relaxation (e.g., via beta-2 adrenergic stimulation), it is not the direct second messenger for **nitric oxide (NO)**-mediated relaxation. - **cAMP** is produced by **adenylyl cyclase** and primarily activates **protein kinase A (PKA)**. *Magnesium* - **Magnesium** is an important cofactor for many enzymes and can influence muscle contraction and relaxation, but it does not serve as a primary second messenger for **nitric oxide (NO)**. - High concentrations of **magnesium** can directly induce muscle relaxation by competing with **calcium** and modulating various channels and enzymes.

Question 346: Which of the following substances is stored in a cell?

A. Thyroxine
B. Renin
C. Cortisol
D. Insulin (Correct Answer)

Explanation: ***Insulin*** - Insulin is a **peptide hormone** synthesized as **proinsulin** and then cleaved into active insulin, which is stored in **secretory granules** within pancreatic **beta cells** before release. - Its storage in vesicles allows for prompt release in response to stimuli like high blood glucose, enabling rapid regulation of **glucose metabolism**. - Insulin represents the **classic example** of intracellular hormone storage in medical physiology. *Cortisol* - Cortisol is a **steroid hormone**, synthesized from **cholesterol** in the adrenal cortex. Steroid hormones are **lipid-soluble** and **not stored** in vesicles; they are released immediately upon synthesis. - Its production is regulated by the **hypothalamic-pituitary-adrenal (HPA) axis**, with synthesis occurring on demand rather than being stored. *Thyroxine* - Thyroxine (T4) is a **thyroid hormone** produced by follicular cells of the thyroid gland, but it is **stored extracellularly** as part of **thyroglobulin** in the colloid, not inside cells in secretory vesicles. - Before release, T4 must be cleaved from thyroglobulin and then secreted, which is distinct from intracellular storage. *Renin* - Renin is an **enzyme** produced by the **juxtaglomerular cells** of the kidney. While renin is stored in granules within these cells, it functions as a **proteolytic enzyme** in the blood rather than as a typical hormone acting on distant receptors. - Its primary role is to cleave **angiotensinogen** in the bloodstream, initiating the **renin-angiotensin-aldosterone system** for blood pressure regulation. - In the context of cellular physiology, **insulin** is the prototypical example of a stored substance due to its role as a classical hormone with direct metabolic effects.

Question 347: Which external factors influence the epigenetic regulation of skeletal growth?

A. External genetic factors that influence skeletal growth
B. Internal genetic factors affecting skeletal growth
C. Genetic factors that do not influence skeletal growth
D. External environmental factors affecting skeletal growth (Correct Answer)

Explanation: ***Correct: External environmental factors affecting skeletal growth*** - **External environmental factors** such as **nutrition**, **exercise**, exposure to **toxins**, and **stress** can significantly influence epigenetic modifications - These epigenetic changes, like **DNA methylation** and **histone modification**, directly impact gene expression related to skeletal development and growth - This is the key mechanism by which environmental exposures regulate skeletal growth patterns *Incorrect: External genetic factors that influence skeletal growth* - This option is contradictory as "external" and "genetic" represent incompatible categories - **Genetic factors** are inherently internal (part of the genome), not external - Epigenetic regulation acts as an interface between genetic predisposition and environmental influences *Incorrect: Internal genetic factors affecting skeletal growth* - While **internal genetic factors** (e.g., genes like *COL1A1*, *GH1*) definitely influence skeletal growth, these are part of the inherited blueprint, not external factors - The question specifically asks about **external** factors influencing epigenetic regulation - Epigenetic modifications alter gene expression patterns without changing the DNA sequence itself *Incorrect: Genetic factors that do not influence skeletal growth* - This option is irrelevant as many genetic factors DO influence skeletal growth - The question asks about factors that **influence** epigenetic regulation, not factors that have no effect - This represents a clearly incorrect distractor

Question 348: Karyotyping is done in which phase of the cell cycle?

A. Anaphase
B. Metaphase (Correct Answer)
C. Telophase
D. S phase

Explanation: ***Metaphase*** - During **metaphase**, chromosomes are maximally condensed and aligned at the **metaphase plate**, making them most visible and easy to distinguish under a microscope. - This condensation and alignment are crucial for accurate visualization and analysis of chromosome number and structure in **karyotyping**. *Anaphase* - In **anaphase**, sister chromatids separate and move to opposite poles, which makes them difficult to organize and analyze systematically for karyotyping. - The chromosomes are in motion and becoming less condensed as they move apart, which is not ideal for imaging. *Telophase* - During **telophase**, chromosomes decondense and nuclear envelopes reform, making them invisible or poorly defined for microscopic analysis. - The cell is also preparing to divide, and the chromosomes are no longer individually distinct structures suitable for karyotyping. *S phase* - The **S (synthesis) phase** is when DNA replication occurs, and chromosomes are replicated but remain in a decondensed state as chromatin. - In this phase, individual chromosomes are not condensed or visible as distinct structures, making them unsuitable for karyotyping.

Question 349: Which of the following helps in cell-to-cell adhesion?

A. Interleukins
B. Interferons
C. E-Cadherin (Correct Answer)
D. Matrix metalloproteinases

Explanation: ***E-Cadherin*** - E-Cadherin is a **cell adhesion molecule** that plays a crucial role in maintaining the structure of tissues by promoting **cell-to-cell adhesion** [1]. - It is mainly involved in the **adherens junctions**, helping cells stick together, especially in epithelial tissues. *Matrix metallo proteinase* - Matrix metallo proteinases (MMPs) are enzymes that degrade **extracellular matrix** components, rather than promoting adhesion between cells. - They are involved in **tissue remodeling** and **wound healing**, not in direct cell-to-cell interactions. *Interleukins* - Interleukins are a group of **cytokines** that mediate **immune responses**, but they do not facilitate direct cell adhesion. - Their primary function involves **cell signaling** and communication, rather than adhesion processes. *Interferons* - Interferons are signaling proteins involved in the **immune defense against viral infections** and do not have a role in cell-to-cell adhesion. - They primarily act to induce an **antiviral state** in neighboring cells and modulate the immune response. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 314-315.

Question 350: Following occurs in living cells only:

A. Simple diffusion
B. Facilitated diffusion
C. Osmosis
D. Active transport (Correct Answer)

Explanation: ***Active transport*** - **Active transport** requires energy (ATP) to move substances against their concentration gradient, a process only possible in **living cells** that can produce ATP. - This process is crucial for maintaining cellular homeostasis, accumulating nutrients, and removing waste, all of which are vital functions of **living organisms**. *Simple diffusion* - **Simple diffusion** is the passive movement of substances across a membrane from an area of higher concentration to lower concentration, without the need for energy or membrane proteins. - This process can occur in **both living and non-living systems**, as it is driven by random molecular motion and concentration gradients. *Facilitated diffusion* - **Facilitated diffusion** involves the passive movement of molecules across a membrane with the help of **transport proteins** (channels or carriers) but still moves down the concentration gradient without direct energy expenditure. - While it uses proteins, these proteins can sometimes function in **isolated membrane systems** even if the cell is not metabolically active (e.g., in a cell lysate). *Osmosis* - **Osmosis** is the specific type of diffusion involving the net movement of **water molecules** across a selectively permeable membrane, driven by differences in solute concentration. - Similar to simple diffusion, osmosis is a **physical process** based on water potential gradients and can occur in both **living and non-living membranes** given the right conditions.

Practice by Chapter

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Cell Cycle and Regulation

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Cellular Aging

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Apoptosis and Cell Death

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