Cellular Physiology Practice Questions

Q: What is the equilibrium potential for potassium (K+) given an extracellular fluid (ECF) concentration of 4 mEq/L and an intracellular fluid (ICF) concentration of 140 mEq/L?

-90 mV. **-90 mV** - The **Nernst equation** is used to calculate the equilibrium potential: E = (61/z) * log([ion]out/[ion]in). For potassium, the charge (z) is +1. - Plugging in the values: E = 61 * log(4/140) = 61 * log(0.02857) = 61 * (-1.544) ≈ **-94.2 mV**, which is closest to -90 mV. *+60 mV* - This value is close to the **equilibrium potential for sodium**, which has a much higher extracellular concentration and a positive equilibrium potential. - It does not reflect the significant concentration gradient of potassium, where the intracellular concentration is much higher. *-60 mV* - While negative, this potential is **not negative enough** to accurately represent the equilibrium potential for potassium with the given concentrations. - A potential of -60 mV falls between the typical resting membrane potential and the potassium equilibrium potential, indicating other ion influences. *+90 mV* - A positive equilibrium potential for potassium would imply that the **extracellular concentration is significantly higher** than the intracellular concentration, which is incorrect. - This value contradicts the physiological reality of potassium distribution across cell membranes.

Q: What generates intracellular signals when cells are subjected to shear stress?

Integrins. ***Integrins*** - **Integrins** are transmembrane receptors that link the extracellular matrix to the cytoskeleton, acting as mechanosensors. - When cells experience **shear stress**, integrins undergo conformational changes that activate intracellular signaling pathways, mediating cellular responses. - They are the **primary mechanotransducers** that directly sense and convert mechanical forces into biochemical signals. *Cadherins* - **Cadherins** are primarily involved in cell-to-cell adhesion, especially in epithelial tissues, forming adherens junctions. - While they contribute to tissue integrity, their primary role is not in sensing and transducing **shear stress** signals. *Selectins* - **Selectins** are a family of cell adhesion molecules involved in initial leukocyte rolling and adhesion to endothelial cells during inflammation. - They bind to carbohydrates on other cells but are not directly involved in the intracellular signaling response to **shear stress**. *Focal adhesion molecules* - **Focal adhesion molecules** are a complex of proteins that includes integrins along with intracellular adaptor proteins like talin, vinculin, and paxillin. - While focal adhesions are important for mechanotransduction, they represent the **downstream signaling complex** rather than the primary receptor that generates the initial signal. - **Integrins** are the specific transmembrane component that directly senses shear stress and initiates the cascade.

Q: Which of the following statements about gap junctions is false?

Intercellular space 1000 nm. ***Intercellular space 1000 nm*** - Gap junctions are characterized by a very narrow intercellular space, typically **2-4 nm**, which allows for direct communication between adjacent cells. - An intercellular space of 1000 nm (1 micrometer) is a large gap, inconsistent with the close apposition required for gap junction function. *Transmit electric signals* - Gap junctions facilitate the **direct passage of ions and small molecules** between cells, enabling the rapid spread of electrical signals. - This property is crucial for coordinated cellular activities, such as in cardiac muscle contraction. *Intercellular space is small* - The narrow intercellular space is a defining feature of gap junctions, bringing the plasma membranes of adjacent cells very close together. - This small distance allows for the formation of **connexons**, which are the channels that bridge the two cells. *Seen in cardiac muscle* - Gap junctions are abundant in cardiac muscle, where they form **intercalated discs** that allow for the rapid and synchronized spread of electrical impulses. - This synchronization is essential for efficient heart contraction.

Q: Which of the following is an ionic channel?

Nicotinic cholinergic receptors. ***Nicotinic cholinergic receptors*** - **Nicotinic cholinergic receptors** are **ligand-gated ion channels** that open upon binding of acetylcholine, allowing the rapid influx of ions, primarily sodium. - This influx of positive ions leads to **depolarization** of the cell membrane, mediating fast synaptic transmission in the central and peripheral nervous systems, as well as at neuromuscular junctions. *Alpha-1 adrenergic receptors* - **Alpha-1 adrenergic receptors** are **G protein-coupled receptors (GPCRs)** that, when activated, lead to the production of **inositol triphosphate (IP3)** and **diacylglycerol (DAG)**. (These secondary messengers increase intracellular calcium and activate protein kinase C, respectively.) - They are primarily involved in smooth muscle contraction, vasoconstriction, and glandular secretion, processes that rely on slower, metabolic changes rather than direct ion flow. *Beta-1 adrenergic receptors* - **Beta-1 adrenergic receptors** are also **G protein-coupled receptors (GPCRs)** that couple to **Gs proteins**, leading to direct activation of **adenylyl cyclase** and increased production of **cyclic AMP (cAMP)**. - This increase in cAMP mediates effects such as increased heart rate and contractility, which are slower and involve cascades of protein phosphorylation rather than direct ion channel activity. *Muscarinic acetylcholine receptors* - **Muscarinic acetylcholine receptors** are a family of **G protein-coupled receptors (GPCRs)**, not ion channels. - Their activation leads to a variety of intracellular signaling cascades, such as the activation of **Gi/o proteins** (leading to decreased cAMP and opening of potassium channels) or **Gq proteins** (leading to IP3/DAG production), resulting in slower and modulatory effects on cell excitability.

Q: Which of the following equations correctly describes the Nernst equation for equilibrium potential of an ion?

EMF = 61 mV * log(Co/Ci). ***EMF = 61 mV * log(Co/Ci)*** - The Nernst equation at **37°C (body temperature)** uses approximately 61 mV as the coefficient when using base-10 logarithm (log₁₀). - This value is derived from RT/zF (gas constant × temperature / valence × Faraday constant) ≈ 26 mV for natural logarithm, which becomes **61 mV when converted to log₁₀** by multiplying by 2.303. - The ratio **Co/Ci (outside concentration/inside concentration)** is the standard convention for cations in biological systems to calculate the **equilibrium potential** across a membrane. - For a univalent cation at 37°C: **E = 61 log(Co/Ci)** mV *EMF = 25 mV * log(Co/Ci)* - While 25-26 mV is the correct RT/F value at 37°C, it is used with the **natural logarithm (ln)** form: E = 26 ln(Co/Ci). - This option incorrectly pairs 25 mV with base-10 logarithm, which underestimates the equilibrium potential. *EMF = 41 mV * log(Co/Ci)* - This value is not a standard physiological constant for the Nernst equation. - It does not accurately represent the conversion factor at body temperature. *EMF = 80 mV * log(Co/Ci)* - This value is significantly higher than the standard constant. - It would lead to substantial overestimation of equilibrium potentials in biological systems.

Q: Which of the following is an example of active transport?

Co-transport of amino acids with sodium. ***Co-transport of amino acids with sodium*** - **Co-transport** (also called symport) involves the movement of two or more substances across a membrane using the same protein carrier, where the movement of at least one substance is **down its electrochemical gradient** (e.g., sodium) to drive the movement of another **against its gradient** (e.g., amino acids or glucose). - This is a form of **secondary active transport** that requires energy indirectly, as the sodium gradient is maintained by the **Na+/K+-ATPase pump**, which directly consumes ATP. - Examples include sodium-glucose cotransporter (SGLT) in intestines and kidneys, and sodium-amino acid cotransporters. *Movement of water across cell membrane* - The movement of water across cell membranes occurs primarily by **osmosis**, a type of **passive diffusion**, often facilitated by **aquaporins**. - **Osmosis** does not directly consume metabolic energy (ATP) but instead relies on the water potential/concentration gradient. - This is a passive process requiring no energy input. *Movement of oxygen across cell membrane* - **Oxygen** is a small, nonpolar molecule that moves across cell membranes by **simple diffusion**, directly passing through the lipid bilayer. - This is a **passive process** that occurs down its concentration gradient and does not require energy or membrane carriers. *Facilitated diffusion of glucose* - **Facilitated diffusion** uses carrier proteins (like GLUT transporters) to move substances down their concentration gradient. - While it requires a protein carrier, it does **not require energy** and is therefore a **passive transport** mechanism, not active transport. - This is often confused with the sodium-glucose cotransporter (SGLT), which IS active transport.

Q: Lysosome with undigested particle inside is known as?

Residual body. ***Residual body*** - A **residual body** is a lysosome that contains **undigested material** after the digestive process is complete. - These bodies can accumulate in cells over time and are sometimes associated with **cellular aging**. *Phagosome* - A **phagosome** is a vesicle formed around a particle engulfed by a cell through **phagocytosis**. - It has not yet fused with a lysosome, so digestion has not begun. *Phagolysosome* - A **phagolysosome** is formed when a **phagosome fuses with a lysosome**, initiating the process of digestion of the engulfed material. - At this stage, the contents are actively being broken down by lysosomal enzymes. *Autophagosome* - An **autophagosome** is a double-membraned vesicle that sequesters cellular components, such as damaged organelles or misfolded proteins, for degradation via **autophagy**. - It eventually fuses with a lysosome to form an autophagolysosome, but it is not itself a lysosome with undigested particles.

Q: Which transport process is mediated by carriers and occurs against the concentration gradient?

Active transport. ***Active transport*** - **Active transport** systems use carrier proteins to move molecules across a membrane **against their concentration gradient**, requiring **metabolic energy** (e.g., from ATP hydrolysis). - This process is crucial for maintaining cellular homeostasis, accumulating specific substances, and establishing ion gradients. *Facilitated diffusion* - **Facilitated diffusion** also uses **carrier proteins**, but it moves substances **down their concentration gradient**, thus **not requiring metabolic energy**. - It increases the rate of diffusion for molecules that cannot easily cross the lipid bilayer, like glucose. *Osmosis* - **Osmosis** is the movement of **water molecules** across a selectively permeable membrane **down their water potential gradient**, driven by solute concentration differences, and does **not involve carrier proteins**. - This process equalizes solute concentrations on both sides of the membrane. *Endocytosis* - **Endocytosis** is a bulk transport mechanism where cells **engulf substances** from outside by forming vesicles from the plasma membrane; it's a form of active transport but **does not typically involve specific carrier proteins** embedded in the membrane for individual molecules. - This process is used for taking in larger molecules, particles, or even other cells.

Q: What is a common feature of both active transport and facilitated diffusion?

Moves substances across a membrane. ***Moves substances across a membrane*** - Both **active transport** and **facilitated diffusion** are fundamental membrane transport processes that move substances across the **cell membrane** - This is the key common feature: both mechanisms facilitate the movement of molecules (ions, nutrients, metabolites) from one side of the membrane to the other - Essential for maintaining **cellular homeostasis**, nutrient uptake, waste removal, and signal transduction *Requires carrier proteins* - This is NOT a universal common feature - **Active transport** always requires specific **carrier proteins** (e.g., Na⁺-K⁺ ATPase) - **Facilitated diffusion** can use either carrier proteins (e.g., GLUT transporters) OR **channel proteins** (e.g., Na⁺ channels, K⁺ channels, aquaporins) - Since facilitated diffusion can occur without carrier proteins (via channels), this is not common to both *Involves energy consumption* - This is a key **differentiating feature**, not a common one - **Active transport** requires **ATP** (primary) or uses electrochemical gradients established by ATP (secondary) to move substances against their concentration gradient - **Facilitated diffusion** is a **passive process** that moves substances down their concentration/electrochemical gradient without energy expenditure - This fundamental difference distinguishes active from passive transport *All of the options* - Incorrect, as only the first statement applies to both transport mechanisms - Options 2 and 3 are either not universal or represent differences rather than commonalities

Q: What is the process of passive transport of molecules through protein pores/channels in the cell membrane?

Diffusion. ***Diffusion*** - **Diffusion** is the net movement of particles from an area of higher concentration to an area of lower concentration without requiring energy. - When diffusion occurs through **protein channels or pores** in the cell membrane, it is specifically termed **facilitated diffusion** or **channel-mediated diffusion**. - This remains a form of **passive transport** as it moves substances down their concentration gradient without ATP expenditure. - Examples include ion channels (Na⁺, K⁺, Ca²⁺) and aquaporins for water transport. *Active transport* - **Active transport** requires energy (typically ATP) to move substances **against** their concentration gradient. - It involves carrier proteins (pumps) like Na⁺-K⁺ ATPase that undergo conformational changes. - This is fundamentally different from passive transport through pores. *Transcytosis* - **Transcytosis** is a vesicular transport mechanism for moving substances across an entire cell. - It combines **endocytosis** on one side and **exocytosis** on the other side. - This is not passive transport through pores but rather bulk transport. *Endocytosis* - **Endocytosis** involves engulfing extracellular substances by forming membrane-bound vesicles. - Types include phagocytosis, pinocytosis, and receptor-mediated endocytosis. - This requires energy and does not involve transport through pores.

Question 1

What is the equilibrium potential for potassium (K+) given an extracellular fluid (ECF) concentration of 4 mEq/L and an intracellular fluid (ICF) concentration of 140 mEq/L?

Accepted Answer

-90 mV

Answer

+60 mV

Answer

-60 mV

Answer

+90 mV

Question 2

What generates intracellular signals when cells are subjected to shear stress?

Accepted Answer

Integrins

Answer

Focal adhesion molecules

Answer

Cadherins

Answer

Selectins

Question 3

Which of the following statements about gap junctions is false?

Accepted Answer

Intercellular space 1000 nm

Answer

Transmit electric signals

Answer

Seen in cardiac muscle

Answer

Intercellular space is small

Question 4

Which of the following is an ionic channel?

Accepted Answer

Nicotinic cholinergic receptors

Answer

Alpha-1 adrenergic receptors

Answer

Beta-1 adrenergic receptors

Answer

Muscarinic acetylcholine receptors

Question 5

Which of the following equations correctly describes the Nernst equation for equilibrium potential of an ion?

Accepted Answer

EMF = 61 mV * log(Co/Ci)

Answer

EMF = 25 mV * log(Co/Ci)

Answer

EMF = 41 mV * log(Co/Ci)

Answer

EMF = 80 mV * log(Co/Ci)

Question 6

Which of the following is an example of active transport?

Accepted Answer

Co-transport of amino acids with sodium

Answer

Movement of water across cell membrane

Answer

Movement of oxygen across cell membrane

Answer

Facilitated diffusion of glucose

Question 7

Lysosome with undigested particle inside is known as?

Accepted Answer

Residual body

Answer

Phagosome

Answer

Phagolysosome

Answer

Autophagosome

Question 8

Which transport process is mediated by carriers and occurs against the concentration gradient?

Accepted Answer

Active transport

Answer

Facilitated diffusion

Answer

Osmosis

Answer

Endocytosis

Question 9

What is a common feature of both active transport and facilitated diffusion?

Accepted Answer

Moves substances across a membrane

Answer

Involves energy consumption

Answer

Requires carrier proteins

Answer

All of the options

Question 10

What is the process of passive transport of molecules through protein pores/channels in the cell membrane?

Accepted Answer

Diffusion

Answer

Transcytosis

Answer

Endocytosis

Answer

Active transport

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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