Cellular Physiology Practice Questions

Q: Which cellular mechanism is predominantly affected by hyperkalemia?

Membrane depolarization. ***Membrane depolarization*** - **Hyperkalemia** primarily causes the resting membrane potential to become less negative, moving it closer to the threshold for an action potential. - This initial depolarization can lead to **increased excitability** of nerve and muscle cells, followed by persistent depolarization that inactivates voltage-gated sodium channels, leading to inexcitability. *Membrane hyperpolarization* - **Hyperpolarization** means the membrane potential becomes more negative, moving further away from the threshold for an action potential. - This effect is typically associated with conditions like **hypokalemia**, where a lower extracellular potassium concentration makes it harder for cells to depolarize. *Intracellular protein synthesis* - **Intracellular protein synthesis** is a complex process involving ribosomes and various RNA molecules. - While electrolyte imbalances can indirectly affect cellular metabolism, **hyperkalemia** does not directly or predominantly impair protein synthesis as its primary mechanism of action. *Cellular osmolarity* - **Cellular osmolarity** is primarily regulated by major solutes like sodium, chloride, and impermeable organic molecules within the cell. - Although potassium is a key intracellular ion, changes in extracellular potassium concentration in **hyperkalemia** do not predominantly or directly alter overall cellular osmolarity to the extent seen with dysnatremias.

Q: How does the activation of phospholipase C by GPCRs affect intracellular calcium levels?

Produces IP3 and DAG, increases Ca2+. ***Produces IP3 and DAG, increases Ca2+*** - Activation of **phospholipase C (PLC)** by GPCRs leads to the hydrolysis of **PIP2 (phosphatidylinositol 4,5-bisphosphate)** into two secondary messengers: **inositol triphosphate (IP3)** and **diacylglycerol (DAG)**. - **IP3** then binds to receptors on the **endoplasmic reticulum**, triggering the release of stored **calcium (Ca2+)** into the cytoplasm, thus increasing intracellular calcium levels. *Activates adenylyl cyclase, increases cAMP* - This describes the **Gαs pathway** of GPCR signaling, where the activated G protein stimulates **adenylyl cyclase** to convert ATP into **cyclic AMP (cAMP)**. - This pathway is distinct from the **Gαq pathway** which activates phospholipase C, and it primarily affects protein phosphorylation rather than direct calcium release. *Inhibits guanylyl cyclase, decreases cGMP* - This pathway involves **cGMP (cyclic GMP)**, which is typically produced by **guanylyl cyclase** and is often associated with nitric oxide signaling or specific GPCRs in photoreceptors. - It is not directly involved in the primary mechanism by which **PLC** activation influences intracellular calcium. *Activates phosphodiesterase, decreases cAMP* - This describes the action of the **Gαi pathway**, where activated G proteins can **inhibit adenylyl cyclase** or activate phosphodiesterases to break down **cAMP**. - While this pathway influences **cAMP levels**, it does not directly lead to the production of **IP3** and the release of **intracellular calcium** that is characteristic of PLC activation.

Q: Why is the S phase of the cell cycle MORE sensitive to radiation compared to the G1 phase?

Increased DNA replication activity. ***Increased DNA replication activity*** - During the **S phase**, the cell is actively replicating its **DNA**, which makes it highly vulnerable to radiation damage. - The DNA strands are **unwound and exposed** at replication forks, creating single-stranded regions that are more susceptible to radiation-induced breaks and damage. - The active **DNA synthesis machinery** means any radiation-induced lesions can be directly incorporated into newly synthesized DNA strands, leading to mutations or chromosomal aberrations. - The presence of multiple **replication forks** throughout the genome provides numerous vulnerable targets for ionizing radiation. *Lower metabolic activity* - This is incorrect because **S phase** actually has *high metabolic activity* to support extensive DNA synthesis, nucleotide production, and histone synthesis. - Lower metabolic activity would not explain increased radiosensitivity; in fact, metabolically active phases tend to be more vulnerable to various insults. *Chromatin condensation state* - While chromatin is indeed **less condensed** in S phase (especially at replication origins), this is a contributing factor but not the primary reason for radiosensitivity. - The key issue is not just accessibility but the **active replication process itself**, where DNA damage can be propagated during synthesis. *Cell cycle checkpoint efficiency* - **Checkpoint efficiency** is a protective mechanism, not a cause of increased sensitivity. - S phase does have checkpoints (intra-S checkpoint), but their presence doesn't explain why this phase is inherently more vulnerable to radiation. - The increased sensitivity stems from the **biological vulnerability during active DNA replication**, independent of checkpoint function.

Q: Which of the following second messengers is involved in the pathway activated by beta-adrenergic receptors?

cAMP. ***Correct: cAMP*** - Beta-adrenergic receptors are **G-protein-coupled receptors (GPCRs)** that, when activated, stimulate **adenylyl cyclase** through a stimulatory G-protein (Gs). - Adenylyl cyclase then catalyzes the conversion of **ATP to cyclic AMP (cAMP)**, which acts as a second messenger in the cell. *Incorrect: cGMP* - **cGMP (cyclic guanosine monophosphate)** is typically associated with the signaling pathways of **nitric oxide** and **natriuretic peptides**, which activate guanylyl cyclase. - It is not directly produced as a second messenger in the classical beta-adrenergic receptor pathway. *Incorrect: IP3* - **IP3 (inositol trisphosphate)** is a second messenger produced by the cleavage of **PIP2 (phosphatidylinositol 4,5-bisphosphate)** by phospholipase C, often activated by **Gq-coupled receptors**. - This pathway leads to the release of **intracellular calcium**, distinct from the beta-adrenergic pathway. *Incorrect: DAG* - **DAG (diacylglycerol)** is also a product of **PIP2 cleavage by phospholipase C**, occurring simultaneously with IP3. - It is involved in activating **protein kinase C**, a pathway not directly linked to beta-adrenergic receptor activation.

Q: What is the primary second messenger that nitric oxide increases in target cells?

cGMP. ***cGMP*** - **Nitric oxide (NO)** directly activates **soluble guanylate cyclase**, an enzyme that catalyzes the conversion of **GTP to cGMP**. - **cGMP** then mediates most of the physiological effects of **NO**, such as **vasodilation** and **smooth muscle relaxation**. *cAMP* - **cAMP** is primarily activated by **adenylyl cyclase**, which is often coupled to G-protein coupled receptors that bind hormones like **epinephrine** or **glucagon**. - **Nitric oxide** does not directly increase **cAMP** levels; its signaling pathway involves a different nucleotide. *Nitric oxide synthase* - **Nitric oxide synthase (NOS)** is the **enzyme** responsible for synthesizing **nitric oxide** from L-arginine, not a second messenger itself. - It produces the signaling molecule, but does not transduce the signal within the target cell. *Soluble guanylate cyclase* - **Soluble guanylate cyclase (sGC)** is the **enzyme** that **nitric oxide** activates, leading to the production of **cGMP**. - While crucial to the pathway, **sGC** is an enzyme, not the second messenger itself; **cGMP** is the molecule that directly mediates downstream effects.

Q: Transport of ascorbic acid to the lens is done by:

SVCT2 (Sodium-dependent Vitamin C Transporter 2). ***SVCT2 (Sodium-dependent Vitamin C Transporter 2)*** - **SVCT2** is the primary transporter responsible for the uptake and accumulation of **ascorbic acid (vitamin C)** in various tissues, including the lens. - This transporter uses a **sodium-dependent mechanism** to actively move vitamin C into cells, maintaining its high concentration essential for antioxidant protection in the lens. *Myoinositol* - **Myoinositol** is a sugar alcohol that plays a role in cellular signaling and is a component of cell membranes. - It is transported into cells by specific inositol transporters, but it is **not involved in ascorbic acid transport**. *Choline* - **Choline** is an essential nutrient involved in neurotransmitter synthesis (**acetylcholine**) and membrane structure. - It has its own dedicated transport systems and is **not involved in the transport of ascorbic acid**. *Taurine* - **Taurine** is an amino acid derivative found in high concentrations in the eye, where it plays roles in osmoregulation and antioxidant defense. - It is transported by **taurine transporters** and is **not responsible for ascorbic acid transport**.

Q: What is the typical resolving power of an electron microscope?

1-5 Å. ***1-5 Å*** - Electron microscopes utilize a **beam of electrons** which have much shorter wavelengths than visible light, allowing for significantly higher resolving power. - A resolving power of 1-5 Å (Angstroms) means they can distinguish between objects that are less than a **nanometer** apart, revealing subcellular structures and even atomic details. *1-5 mm* - This range represents a resolution visible to the **unaided human eye** or with very low-power magnification, dramatically less precise than an electron microscope. - It would not allow for the observation of **cellular details** or organelles, which are the primary targets of electron microscopy. *1-5 µm* - This resolution is typical of a **conventional light microscope**, which uses visible light to magnify samples. - While sufficient for observing cells and larger organelles like mitochondria, it is insufficient to visualize **viruses** or intracellular structures at high detail. *1-5 nm* - While 1-5 nanometers (nm) is a very high resolution, a typical electron microscope, especially a **transmission electron microscope (TEM)**, can achieve even finer details, down to the Angstrom scale. - This range is a good approximation for the resolution limit of very advanced **scanning electron microscopes (SEM)** but not the ultimate capability across all electron microscopy.

Q: What is the consequence of inhibiting Na⁺/K⁺ ATPase?

Increased Ca²⁺ in the cell. ***Increased Ca²⁺ in the cell*** - Inhibition of **Na⁺/K⁺ ATPase** leads to an increase in intracellular sodium, which in turn reduces the efficiency of the **Na⁺/Ca²⁺ exchanger**. - This impaired Na⁺/Ca²⁺ exchange results in **less calcium being expelled** from the cell, causing increased intracellular Ca²⁺. *Decreased Na⁺ in the cell* - The **Na⁺/K⁺ ATPase** actively pumps sodium out of the cell; inhibiting it would cause an **increase, not a decrease**, in intracellular Na⁺ concentration. - This option incorrectly states the direct effect of Na⁺/K⁺ ATPase inhibition on intracellular sodium levels. *Increased K⁺ in the cell* - The **Na⁺/K⁺ ATPase** actively pumps potassium into the cell; inhibiting it would lead to a **decrease, not an increase**, in intracellular K⁺ concentration. - This is because the pump is unable to transport extracellular K⁺ into the cell against its concentration gradient. *Increased Cl⁻ in the cell* - **Chloride ion (Cl⁻)** transport is generally managed by different channels and transporters, such as **Cl⁻ channels** or **Na⁺/K⁺/2Cl⁻ cotransporters**, and is not directly regulated by the Na⁺/K⁺ ATPase. - While changes in cell potential due to Na⁺/K⁺ ATPase inhibition might indirectly affect other ion movements, a direct and significant increase in intracellular Cl⁻ is not a primary consequence.

Q: Which of the following organelles is primarily responsible for cellular respiration?

Mitochondria. ***Mitochondria*** - This organelle is often referred to as the "**powerhouse of the cell**" because it is the primary site of **ATP synthesis** through aerobic respiration. - Cellular respiration involves a series of metabolic reactions that convert nutrients into **adenosine triphosphate (ATP)**, providing energy for cellular functions. *Endoplasmic Reticulum* - The **endoplasmic reticulum** is primarily involved in **protein synthesis** (rough ER) and **lipid synthesis** and detoxification (smooth ER). - It does not play a direct role in the production of bulk cellular energy via cellular respiration. *Lysosome* - **Lysosomes** are responsible for **waste breakdown**, recycling cellular debris, and degrading foreign substances through their digestive enzymes. - They are not involved in the processes of cellular respiration or energy production. *Nucleus* - The **nucleus** contains the cell's **genetic material** (DNA) and controls cell growth, metabolism, and reproduction by regulating gene expression. - While it controls cellular processes, it does not directly perform cellular respiration.

Q: Which of the following statements is true regarding heterophilic interactions?

Involved in cell adhesion. ***Involved in cell adhesion*** - Heterophilic interactions refer to binding between **two different types of molecules** or cells. - This type of binding is fundamental to **cell-to-cell adhesion**, where dissimilar molecules on adjacent cell surfaces interact to form stable connections. - Examples include **integrins binding to ECM proteins** (fibronectin, laminin), and **selectins binding to carbohydrate ligands**. - This is the **primary and most general defining feature** of heterophilic interactions. *Bind to the same ligand or hormone* - This describes **homophilic interactions** or typical specific receptor-ligand binding. - Heterophilic interactions involve **dissimilar binding partners**, not identical ones. *Involved in immune response signaling* - While this statement is actually true (heterophilic interactions are crucial in immune responses like T cell receptor-MHC binding, CD28-B7 interactions, and selectin-mediated leukocyte rolling), it represents a **specific application** rather than the fundamental defining characteristic. - **Cell adhesion is the more general and primary function** that encompasses immune and non-immune contexts. *Involved in binding of growth hormone (GH) to specific receptors on the cell membrane* - This is an example of a specific **ligand-receptor interaction** with high specificity. - It does not represent the broader concept of heterophilic interactions as a general mechanism of binding between dissimilar molecular entities.

Question 1

Which cellular mechanism is predominantly affected by hyperkalemia?

Accepted Answer

Membrane depolarization

Answer

Membrane hyperpolarization

Answer

Intracellular protein synthesis

Answer

Cellular osmolarity

Question 2

How does the activation of phospholipase C by GPCRs affect intracellular calcium levels?

Accepted Answer

Produces IP3 and DAG, increases Ca2+

Answer

Activates adenylyl cyclase, increases cAMP

Answer

Inhibits guanylyl cyclase, decreases cGMP

Answer

Activates phosphodiesterase, decreases cAMP

Question 3

Why is the S phase of the cell cycle MORE sensitive to radiation compared to the G1 phase?

Accepted Answer

Increased DNA replication activity

Answer

Lower metabolic activity

Answer

Chromatin condensation state

Answer

Cell cycle checkpoint efficiency

Question 4

Which of the following second messengers is involved in the pathway activated by beta-adrenergic receptors?

Accepted Answer

cAMP

Answer

cGMP

Answer

IP3

Answer

DAG

Question 5

What is the primary second messenger that nitric oxide increases in target cells?

Accepted Answer

cGMP

Answer

Soluble guanylate cyclase

Answer

cAMP

Answer

Nitric oxide synthase

Question 6

Transport of ascorbic acid to the lens is done by:

Accepted Answer

SVCT2 (Sodium-dependent Vitamin C Transporter 2)

Answer

Myoinositol

Answer

Choline

Answer

Taurine

Question 7

What is the typical resolving power of an electron microscope?

Accepted Answer

1-5 Å

Answer

1-5 mm

Answer

1-5 µm

Answer

1-5 nm

Question 8

What is the consequence of inhibiting Na⁺/K⁺ ATPase?

Accepted Answer

Increased Ca²⁺ in the cell

Answer

Decreased Na⁺ in the cell

Answer

Increased K⁺ in the cell

Answer

Increased Cl⁻ in the cell

Question 9

Which of the following organelles is primarily responsible for cellular respiration?

Accepted Answer

Mitochondria

Answer

Endoplasmic Reticulum

Answer

Lysosome

Answer

Nucleus

Question 10

Which of the following statements is true regarding heterophilic interactions?

Accepted Answer

Involved in cell adhesion

Answer

Bind to the same ligand or hormone

Answer

Involved in immune response signaling

Answer

Involved in binding of growth hormone (GH) to specific receptors on the cell membrane

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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