Cellular Physiology Practice Questions

Q: The endoplasmic reticulum does not participate in which of the following processes?

Muscle contraction. **Explanation:** The **Endoplasmic Reticulum (ER)** is a multifunctional organelle divided into Rough ER (RER) and Smooth ER (SER). While it plays a central role in biosynthesis and calcium storage, it does not directly participate in the mechanical process of **muscle contraction**. * **Why Option B is correct:** Muscle contraction is a mechanical process occurring in the **sarcomere** through the interaction of actin and myosin filaments (Sliding Filament Theory). While the **Sarcoplasmic Reticulum** (a specialized form of SER) is crucial for storing and releasing calcium ions to *initiate* contraction, the ER itself does not participate in the contractile process. * **Why Option A is incorrect:** The **Rough ER**, studded with ribosomes, is the primary site for the synthesis of secretory, lysosomal, and membrane-bound proteins. * **Why Option C is incorrect:** The ER is the first step in the secretory pathway. It performs **protein sorting** by identifying proteins with specific signal sequences and packaging them into COPII-coated vesicles for transport to the Golgi apparatus. * **Why Option D is incorrect:** **N-linked glycosylation** (the addition of sugar chains to nitrogen atoms of asparagine) begins in the lumen of the Rough ER, making it essential for glycoprotein synthesis. **High-Yield Facts for NEET-PG:** * **Sarcoplasmic Reticulum (SR):** The specialized SER in muscle cells. Its primary function is **Calcium sequestration** via SERCA pumps. * **N-linked vs. O-linked Glycosylation:** N-linked starts in the **ER**; O-linked occurs exclusively in the **Golgi apparatus**. * **Detoxification:** The SER in hepatocytes contains the **Cytochrome P450** system, essential for drug metabolism. * **Protein Quality Control:** The ER contains "chaperones" (e.g., BiP, Calnexin) that ensure proteins are folded correctly before exiting. Misaligned proteins lead to **ER Stress** and the Unfolded Protein Response (UPR).

Q: The graph below denotes the transport kinetics across the cell membrane. The solute is:

Glucose. ***Glucose*** - The saturation kinetics curve (Michaelis-Menten-like) with a **plateau at Vmax** is characteristic of **facilitated diffusion** via **GLUT transporters**. - Shows **carrier-mediated transport** where transporters become saturated at high glucose concentrations, unlike simple diffusion. *Oxygen* - Crosses membranes by **simple diffusion** following **Fick's law**, showing a **linear relationship** between concentration and transport rate. - Does not exhibit **saturation kinetics** as it doesn't require specific carriers or channels for transport. *Sodium* - Primarily transported by **active transport** via **Na+/K+-ATPase pumps**, which would show different kinetics than the graph. - Active transport can work **against concentration gradients** and typically shows different curve patterns with energy dependence. *Chloride* - Moves across membranes through **ion channels** or **simple diffusion**, exhibiting **linear kinetics** without saturation. - Does not require **carrier proteins** that would create the saturation pattern shown in the graph.

Q: Which of the following is not a function of the smooth endoplasmic reticulum?

Protein synthesis. The Smooth Endoplasmic Reticulum (SER) is a multifunctional organelle characterized by the absence of ribosomes on its surface, which dictates its physiological roles. **Why Protein Synthesis is the Correct Answer:** Protein synthesis is the primary function of the **Rough Endoplasmic Reticulum (RER)**. The RER is studded with ribosomes, which are the sites of translation. Proteins synthesized here are typically destined for secretion, incorporation into the cell membrane, or storage in lysosomes. Since the SER lacks ribosomes, it cannot perform protein synthesis. **Analysis of Incorrect Options:** * **Lipid Synthesis:** The SER contains enzymes necessary for the synthesis of phospholipids, cholesterol, and steroid hormones (e.g., testosterone, estrogen, and cortisol). * **Metabolism of Drugs:** The SER in hepatocytes contains the **Cytochrome P450 system**, which is essential for the detoxification of drugs (like phenobarbital) and various toxins. * **Supply of Calcium:** In muscle cells, the SER is specialized as the **Sarcoplasmic Reticulum**, which stores and releases calcium ions ($Ca^{2+}$) to trigger muscle contraction. **High-Yield NEET-PG Pearls:** * **Nissl Bodies:** These are large granules of RER found in neurons; they are responsible for high-rate protein synthesis. * **Sarcoplasmic Reticulum:** A specialized SER in myocytes that regulates excitation-contraction coupling via calcium sequestration. * **Hypertrophy of SER:** Chronic use of certain drugs (e.g., barbiturates) can lead to the hypertrophy of the SER in liver cells due to enzyme induction, contributing to drug tolerance.

Q: An increase in extracellular K+ concentration leads to what change in the resting membrane potential (RMP)?

Decrease in RMP. **Explanation:** The Resting Membrane Potential (RMP) of a cell is primarily determined by the concentration gradient of Potassium ($K^+$) across the cell membrane, as the membrane is highly permeable to $K^+$ at rest. This relationship is governed by the **Nernst Equation**. **1. Why Option A is Correct:** Under normal conditions, $K^+$ concentration is much higher inside the cell (~140 mEq/L) than outside (~4 mEq/L). This steep gradient drives $K^+$ to leak out, leaving the interior electronegative (approx. –70 to –90 mV). When **extracellular $K^+$ increases** (Hyperkalemia), the concentration gradient between the inside and outside of the cell decreases. Consequently, less $K^+$ leaves the cell, and the interior becomes less negative (e.g., moving from –90 mV to –70 mV). In physiological terms, moving toward zero is a **decrease in the magnitude of the RMP** (Depolarization). **2. Why Other Options are Incorrect:** * **Options B & D:** While the RMP does change, the relationship is logarithmic (as per the Nernst Equation), not a fixed linear increase of –10 or –20 mV per 10 mEq/L. Furthermore, an "increase" in RMP usually implies becoming more negative (hyperpolarization), which is the opposite of what occurs in hyperkalemia. * **Option C:** RMP is extremely sensitive to extracellular $K^+$ levels; therefore, "no change" is physiologically impossible. **Clinical Pearls for NEET-PG:** * **Hyperkalemia:** Leads to partial depolarization, making cells initially more excitable, but eventually causes inactivation of $Na^+$ channels, leading to cardiac arrhythmias (Tall T-waves on ECG). * **Hypokalemia:** Increases the concentration gradient, causing $K^+$ to exit the cell more rapidly, leading to **Hyperpolarization** (RMP becomes more negative/increases in magnitude). * **Goldman-Hodgkin-Katz Equation:** Used instead of Nernst when considering multiple ions ($Na^+, K^+, Cl^-$) simultaneously.

Q: Connexins are associated with which of the following?

Gap junctions. **Explanation:** **Gap Junctions (The Correct Answer):** Gap junctions are specialized intercellular connections that allow the direct passage of ions and small molecules (up to 1000 Da) between adjacent cells. They are composed of transmembrane proteins called **Connexins**. Six connexin molecules assemble to form a hemichannel known as a **Connexon**. When connexons from two neighboring cells align, they form a complete aqueous channel. These junctions are vital for electrical coupling (e.g., in cardiac muscle and smooth muscle) and chemical signaling. **Why other options are incorrect:** * **Desmosomes (Macula Adherens):** These are "spot welds" that provide mechanical strength to tissues. They utilize **Cadherins** (specifically Desmoglein and Desmocollin) linked to intermediate filaments (keratin). * **Hemidesmosomes:** These anchor the basal surface of epithelial cells to the underlying basement membrane. They primarily involve **Integrins**, not connexins. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac Physiology:** Gap junctions are the structural basis of the **Intercalated Discs**, allowing the heart to function as a functional syncytium. * **Clinical Correlation:** Mutations in Connexin genes are linked to specific pathologies: * **Connexin 26:** Mutations are the most common cause of congenital non-syndromic **sensorineural deafness**. * **Connexin 32:** Linked to X-linked **Charcot-Marie-Tooth disease**. * **Connexin 46/50:** Associated with congenital **cataracts**. * **Permeability:** Gap junction permeability is regulated by intracellular pH and Ca²⁺ levels (high Ca²⁺ or low pH typically closes the channels).

Question 1

The electrogenic Na/K ATPase plays a critical role in cellular physiology by?

Accepted Answer

Using energy in ATP to extrude 3 Na+ out of cells in exchange for taking two K+ into the cell.

Answer

Using energy in ATP to extrude 3 K+ out of cells in exchange for taking Na+ into the cell.

Answer

Using the energy in moving Na+ into the cell or K+ outside the cell to make ATP.

Answer

Using energy in moving Na+ outside of cell or K+ inside the cell to make ATP.

Question 2

The endoplasmic reticulum does not participate in which of the following processes?

Accepted Answer

Muscle contraction

Answer

Protein synthesis

Answer

Protein sorting

Answer

Glycoprotein synthesis

Question 3

The graph below denotes the transport kinetics across the cell membrane. The solute is:

Accepted Answer

Glucose

Answer

Oxygen

Answer

Sodium

Answer

Chloride

Question 4

Which of the following is not a function of the smooth endoplasmic reticulum?

Accepted Answer

Protein synthesis

Answer

Lipid synthesis

Answer

Metabolism of drugs

Answer

Supply of calcium for cellular functions

Question 5

Which of the following is NOT true about active transport?

Accepted Answer

It is unidirectional

Answer

It is saturable

Answer

It requires energy

Answer

It is a carrier-mediated process

Question 6

The cell membrane is permeable to three ions, X, Y, and Z. The equilibrium potentials for ions X and Y are -50 mV and -30 mV, respectively. If the resting membrane potential (RMP) is such that there is no net electrogenic transfer, what is the equilibrium potential for ion Z?

Accepted Answer

80

Answer

-130

Answer

10

Answer

-50

Question 7

What is the resting membrane potential of a cell?

Accepted Answer

Dependent on the permeability of the cell membrane to K+ being greater than to Na+.

Answer

Falls to zero if Na+/K+ ATPase in the membrane is inhibited.

Answer

Equal to the equilibrium potential for K+.

Answer

Equal to the equilibrium potential of Na+.

Question 8

An increase in extracellular K+ concentration leads to what change in the resting membrane potential (RMP)?

Accepted Answer

Decrease in RMP

Answer

Increase in RMP by –10 mV for each 10 mEq/L increase in K+

Answer

No change in RMP

Answer

Increase in RMP by –20 mV for each 10 mEq/L increase in K+

Question 9

Connexins are associated with which of the following?

Accepted Answer

Gap junctions

Answer

Desmosomes

Answer

Hemidesmosomes

Answer

None of the above

Question 10

Mad cow disease is caused by what?

Accepted Answer

Protein misfolding

Answer

Bacterial infection

Answer

Viral infection

Answer

Spirochete infection

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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