Cellular Physiology Practice Questions

Q: All of the following statements regarding the Golgi apparatus are true, EXCEPT:

It is a nonpolarized structure.. **Explanation:** The Golgi apparatus is a highly organized organelle essential for the modification, sorting, and packaging of proteins and lipids. **Why Option C is the correct answer:** The Golgi apparatus is a **highly polarized** structure, both morphologically and functionally. It possesses two distinct faces with different biochemical compositions and enzymatic activities. Stating that it is "nonpolarized" is factually incorrect, making it the right choice for an "EXCEPT" question. **Analysis of other options:** * **Option A (Cis face is the receiving end):** This is true. The *cis* face (forming face) is convex and oriented toward the endoplasmic reticulum (ER). It receives transport vesicles containing newly synthesized proteins from the ER. * **Option B (Trans face is the secretory end):** This is true. The *trans* face (maturing face) is concave and oriented toward the plasma membrane. It acts as the exit portal where proteins are sorted into secretory vesicles for their final destinations. * **Option D (Situated near the nucleus):** This is true. In most animal cells, the Golgi complex is localized in the perinuclear region, often held in place by the microtubule network near the centrosome. **High-Yield NEET-PG Pearls:** * **Function:** The Golgi is the primary site for **glycosylation** (addition of sugar moieties), sulfation, and phosphorylation of proteins. * **I-Cell Disease:** A clinical correlation where a deficiency in the enzyme *phosphotransferase* prevents the tagging of lysosomal enzymes with **Mannose-6-Phosphate** in the Golgi. This leads to enzymes being secreted extracellularly rather than sent to lysosomes. * **Silver Staining:** The Golgi was first identified by Camillo Golgi using the "black reaction" (silver nitrate stain).

Q: What is true about the Na+-K+ pump?

It involves ATPase activity.. The **Na⁺-K⁺ ATPase pump** is a classic example of **Primary Active Transport**, essential for maintaining cellular resting membrane potential and volume. ### **Explanation of the Correct Option** **A. It involves ATPase activity:** The pump is an enzyme (Na⁺-K⁺ ATPase) located on the plasma membrane. It requires energy to move ions against their concentration gradients. It catalyzes the hydrolysis of **ATP into ADP and inorganic phosphate**, using the released energy to drive the conformational changes necessary for ion transport. ### **Why Other Options are Incorrect** * **B. It can move Na⁺ both into and out of the cell:** This is incorrect. The pump is unidirectional; it **only** moves Na⁺ from the intracellular fluid to the extracellular fluid (against its gradient). * **C. It is electrically neutral:** This is incorrect. The pump is **electrogenic**. Because it moves 3 positive charges out and only 2 in, it creates a net deficit of positive ions inside the cell, contributing to the negativity of the Resting Membrane Potential (RMP). * **D. It pumps out one Na⁺ for one K⁺:** The stoichiometry is fixed at **3 Na⁺ ions out** and **2 K⁺ ions in** for every molecule of ATP hydrolyzed. ### **High-Yield NEET-PG Pearls** * **Inhibitor:** The pump is specifically inhibited by **Cardiac Glycosides** (e.g., **Ouabain** and **Digoxin**), which bind to the extracellular alpha subunit. * **Structure:** It is a heterodimer consisting of an **alpha subunit** (catalytic site, ion binding, ATP binding) and a **beta subunit** (essential for membrane localization). * **Function:** It accounts for nearly **25-30%** of the total energy expenditure in a resting cell (up to 70% in neurons). * **Insulin & Epinephrine:** Both hormones stimulate the pump, shifting K⁺ into cells (used clinically to treat hyperkalemia).

Q: Which statement is TRUE regarding the Na+/K+ pump?

Two potassium ions are exchanged for five sodium ions.. **Explanation:** The **Na+/K+ ATPase (Sodium-Potassium Pump)** is a primary active transporter found in the membranes of almost all animal cells. It plays a critical role in maintaining resting membrane potential and cell volume. **1. Why Option B is Correct:** The pump operates by transporting **3 Na⁺ ions out** of the cell and **2 K⁺ ions into** the cell for every molecule of ATP hydrolyzed. This stoichiometry (3:2 ratio) makes the pump **electrogenic**, as it creates a net deficit of positive charges inside the cell, contributing to the negative resting membrane potential. **2. Analysis of Incorrect Options:** * **Option A:** Both ions are pumped against their concentration gradients. However, while Na⁺ is pumped against its electrochemical gradient, K⁺ is pumped against its chemical gradient but *along* the electrical gradient (since the cell interior is negative). Therefore, the statement is partially incomplete compared to the specific stoichiometry of Option B. * **Option C:** Hypercalcemia does not arrest the pump. However, **Digitalis (Cardiac glycosides)** like Digoxin specifically inhibit the pump by binding to the extracellular alpha-subunit. * **Option D:** An increase in intracellular sodium actually *decreases* the concentration gradient for Na⁺ influx, which would typically decrease the amplitude of the action potential, not increase it. **High-Yield NEET-PG Pearls:** * **Structure:** It is a P-type ATPase consisting of $\alpha$ (catalytic), $\beta$, and $\gamma$ subunits. * **Inhibitors:** Ouabain and Digoxin. * **Stimulators:** Insulin, Aldosterone, and Beta-adrenergic agonists (all shift K⁺ into cells, potentially causing hypokalemia). * **Energy Consumption:** It accounts for approximately 30-40% of the total energy expenditure in a resting cell (up to 70% in neurons).

Q: The electrical potential difference necessary for a single ion to be at equilibrium across a membrane is best described by which equation?

Nernst equation. ### Explanation **1. Why the Nernst Equation is Correct:** The **Nernst equation** is used to calculate the **equilibrium potential** (also called the Nernst potential) for a **single ion**. It represents the electrical potential difference across a membrane that exactly balances the concentration gradient of that specific ion, resulting in no net movement of the ion into or out of the cell. * **Formula:** $E = \frac{61}{z} \times \log \frac{[Ion]_{outside}}{[Ion]_{inside}}$ (at body temperature). * **Key Concept:** It assumes the membrane is permeable to only one ion at a time. **2. Why the Other Options are Incorrect:** * **A. Goldman Equation:** Unlike the Nernst equation, the Goldman-Hodgkin-Katz (GHK) equation calculates the **Resting Membrane Potential (RMP)** by considering the concentrations and **permeabilities of multiple ions** (primarily $Na^+$, $K^+$, and $Cl^-$) simultaneously. * **B. Van't Hoff Equation:** This equation is used to calculate **osmotic pressure** based on the concentration of solutes in a solution. It is unrelated to electrical potentials. * **C. Fick's Law:** This describes the **rate of diffusion** of a gas or solute across a membrane. It states that the flux is proportional to the concentration gradient and surface area but does not calculate electrical equilibrium. **3. High-Yield Clinical Pearls for NEET-PG:** * **RMP of a Neuron:** Typically **-70 mV**, which is closest to the equilibrium potential of $K^+$ (-94 mV) because the resting membrane is most permeable to Potassium. * **Equilibrium Potentials to Remember:** * $K^+$: -94 mV * $Na^+$: +61 mV * $Cl^-$: -70 to -90 mV * $Ca^{2+}$: +132 mV * **The Sodium-Potassium Pump ($Na^+/K^+$ ATPase):** It is **electrogenic**, contributing about -4 mV to the RMP by pumping 3 $Na^+$ out for every 2 $K^+$ in.

Q: Activation of G-protein regulates all of the following except?

Transcription factor. **Explanation:** G-protein coupled receptors (GPCRs) are the largest family of cell surface receptors. They act as molecular switches that transmit signals from extracellular ligands to intracellular effectors via heterotrimeric G-proteins ($\alpha$, $\beta$, and $\gamma$ subunits). **Why "Transcription Factor" is the correct answer:** Transcription factors are typically regulated by **nuclear receptors** (e.g., steroid hormones) or via complex downstream kinase cascades (like the MAPK pathway). While G-protein signaling can *eventually* influence gene expression, G-proteins do not **directly** regulate transcription factors. Transcription factors are located in the nucleus, whereas G-proteins are membrane-bound peripheral proteins. **Analysis of Incorrect Options:** * **Adenyl cyclase activity:** This is a classic G-protein function. $G_s$ stimulates and $G_i$ inhibits Adenyl Cyclase, which converts ATP to cAMP (the second messenger). * **Ion channels:** G-proteins can regulate ion channels either directly (e.g., $G_{\beta\gamma}$ subunits opening $K^+$ channels in the heart) or indirectly via second messengers (e.g., cAMP-dependent phosphorylation of $Ca^{2+}$ channels). * **IP3 & DAG:** The $G_q$ protein activates Phospholipase C (PLC), which cleaves membrane phospholipids into Inositol triphosphate (IP3) and Diacylglycerol (DAG), leading to calcium release and Protein Kinase C activation. **High-Yield Clinical Pearls for NEET-PG:** * **Toxins:** *Vibrio cholerae* toxin causes permanent activation of $G_s$ (inhibits GTPase activity), leading to secretory diarrhea. *Bordetella pertussis* toxin inhibits $G_i$, leading to increased cAMP levels. * **Structure:** GPCRs are also known as **7-transmembrane** or **Serpentine receptors**. * **Termination:** The signal is terminated when the $\alpha$-subunit hydrolyzes GTP to GDP (intrinsic GTPase activity).

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.

Question 1

All of the following statements regarding the Golgi apparatus are true, EXCEPT:

Accepted Answer

It is a nonpolarized structure.

Answer

The cis face is the receiving end.

Answer

The trans face is the secretory end.

Answer

It is situated near the nucleus.

Question 2

What is true about the Na+-K+ pump?

Accepted Answer

It involves ATPase activity.

Answer

It can move Na+ both into and out of the cell.

Answer

It is electrically neutral.

Answer

It pumps out one Na+ for one K+.

Question 3

Which statement is TRUE regarding the Na+/K+ pump?

Accepted Answer

Two potassium ions are exchanged for five sodium ions.

Answer

Potassium is pumped against its electrochemical gradient.

Answer

Hypercalcemia causes arrest of the Na+/K+ pump.

Answer

An increase in intracellular sodium increases the action potential.

Question 4

The electrical potential difference necessary for a single ion to be at equilibrium across a membrane is best described by which equation?

Accepted Answer

Nernst equation

Answer

Goldman equation

Answer

Van't Hoff equation

Answer

Fick's law

Question 5

Activation of G-protein regulates all of the following except?

Accepted Answer

Transcription factor

Answer

Adenyl cyclase activity

Answer

Ion channels

Answer

IP3 & DAG

Question 6

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 7

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

Accepted Answer

Glucose

Answer

Oxygen

Answer

Sodium

Answer

Chloride

Question 8

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 9

A cell membrane is damaged by a needle. How does the repair occur?

Accepted Answer

Resealing by the lipid bilayer

Answer

Lateral movements of proteins

Answer

Enzymatic reactions

Answer

Calcium facilitated by membrane repair

Question 10

Which statement about the following cellular phenomenon is false?

Accepted Answer

Clathrin-mediated endocytosis is involved in the uptake of dead tissues and bacteria.

Answer

This phenomenon includes phagocytosis and pinocytosis.

Answer

It leads to endosome formation.

Answer

None of the above.

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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