Cellular Physiology Practice Questions

Q: 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?

Paracrine. ***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.

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

E-Cadherin. ***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.

Q: Following occurs in living cells only:

Active transport. ***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.

Q: Which of the following statements about the Na-K pump is false?

It is located on the apical membrane of cell. ***It is located on the apical membrane of cell*** - The **Na-K pump**, or **Na+/K+-ATPase**, is primarily located on the **basolateral membrane** of epithelial cells, not **apical membrane**. - Its strategic placement on the basolateral membrane is crucial for maintaining cellular polarity and driving transepithelial transport processes, such as reabsorption in the kidneys. *It is electrogenic* - The Na-K pump is indeed **electrogenic** because it transports three **Na+ ions** out of the cell for every two **K+ ions** pumped in. - This unequal charge distribution creates a net movement of one positive charge out of the cell, contributing to the **resting membrane potential**. *It is not directly involved in the generation of action potentials.* - While the Na-K pump is essential for **maintaining the ion gradients** necessary for **action potentials**, it is not directly involved in their rapid depolarization or repolarization phases. - Action potentials are primarily generated by the rapid opening and closing of **voltage-gated ion channels** (e.g., Na+ and K+ channels). *It needs ATP for its functioning* - The Na-K pump is an **active transport mechanism** that moves ions against their concentration gradients, requiring **energy in the form of ATP hydrolysis**. - This **ATP-dependent process** ensures the continuous maintenance of the Na+ and K+ gradients, crucial for various cellular functions, including nerve impulse transmission and muscle contraction.

Q: Cell-to-cell permeability occurs through

Connexins. ***Connexins*** - **Connexins** are the proteins that form **gap junctions**, which are specialized intercellular channels that allow direct passage of ions and small molecules between adjacent cells. - These channels facilitate **cell-to-cell communication** and regulate permeability by enabling the rapid exchange of electrical and chemical signals. *Occludin* - **Occludin** is a key protein component of **tight junctions** (zona occludens), which are primarily responsible for sealing the space between cells and preventing paracellular leakage. - Tight junctions **restrict cell-to-cell permeability** rather than promoting it, defining tissue polarity. *Zona adherens* - The **zona adherens** (adherens junctions) are cell junctions that provide strong **mechanical attachment** between cells through the binding of adjacent cell membranes. - They are involved in maintaining tissue integrity and cell shape but do not directly regulate **cell-to-cell permeability** of substances. *Zonulin* - **Zonulin** is a protein that modulates **intestinal tight junction permeability**, acting as a regulator of the paracellular pathway. - While it affects permeability, it does so by *loosening tight junctions*, not by forming direct cell-to-cell channels that allow substance passage.

Q: Which of the following characteristics is shared by both active transport and facilitated diffusion?

Requires specific carrier proteins. ***Requires specific carrier proteins*** - Both **active transport** and **facilitated diffusion** rely on specific **transmembrane proteins** to move substances across the cell membrane. - These carrier proteins bind to the specific molecule they transport, undergoing conformational changes that facilitate its movement. *Does not require energy input* - This statement is only true for **facilitated diffusion**, which is a form of passive transport. - **Active transport** requires an input of **metabolic energy**, typically in the form of ATP, to move substances. *Transports solute down concentration gradient* - This is characteristic of **facilitated diffusion**, where molecules move from an area of higher concentration to an area of lower concentration. - **Active transport** moves solutes **against** their concentration gradient, requiring energy. *Transports solute against concentration gradient* - This is a defining feature of **active transport**, which allows cells to accumulate substances even when their external concentration is lower. - **Facilitated diffusion** moves solutes **down** their concentration gradient and cannot transport against a gradient.

Q: What is the process of translocation through pores in cell membranes?

Facilitated diffusion. ***Facilitated diffusion*** - This process involves the movement of molecules across the cell membrane **down their concentration gradient** with the help of **specific membrane proteins**, without the expenditure of cellular energy. - When the question refers to "pores," it specifically means **channel proteins** (also called pore proteins), which form aqueous pathways through the membrane for ions and small polar molecules. - **Facilitated diffusion** includes both channel-mediated transport (through pores) and carrier-mediated transport (through conformational changes), making it the correct answer. - This allows substances that cannot easily pass through the lipid bilayer to traverse the membrane passively. *Transcytosis* - This is a type of **vesicular transport** that involves the transport of substances across an entire cell, typically from one extracellular space to another, using **endocytosis** and **exocytosis**. - It does not involve direct translocation through membrane pores but rather the formation and movement of vesicles. *Endocytosis* - This is a process by which cells **engulf extracellular material** by forming vesicles from the plasma membrane. - It involves the invagination of the cell membrane to internalize substances, not their passage through pre-existing pores or channels. *Active transport* - This process moves molecules **against their concentration gradient**, requiring direct or indirect **expenditure of cellular energy** (ATP). - While it often uses protein carriers or pumps, it is distinguished by its energy requirement and ability to move substances uphill, unlike facilitated diffusion which is passive movement down the gradient.

Question 1

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?

Accepted Answer

Paracrine

Answer

Neural

Answer

Endocrine

Answer

Neuroendocrine

Question 2

Which of the following statements about G protein-coupled receptors (GPCRs) is correct?

Accepted Answer

The alpha subunit of G proteins determines whether they are stimulatory or inhibitory.

Answer

G proteins bind hormones directly before transmitting signals to receptors.

Answer

G proteins are active when bound to GDP and inactive when bound to GTP.

Answer

G proteins require the beta and gamma subunits to remain bound to the alpha subunit to transmit signals.

Question 3

Which of the following helps in cell-to-cell adhesion?

Accepted Answer

E-Cadherin

Answer

Interleukins

Answer

Interferons

Answer

Matrix metalloproteinases

Question 4

Following occurs in living cells only:

Accepted Answer

Active transport

Answer

Simple diffusion

Answer

Facilitated diffusion

Answer

Osmosis

Question 5

Which one of the following statements about the gap junction is true?

Accepted Answer

It permits the passage of ions from one cell to an adjacent cell.

Answer

It extends as a zone around the apical perimeter of adjacent cells.

Answer

Its adhesion is dependent upon calcium ions.

Answer

It possesses dense plaques composed in part of desmoplakins.

Question 6

Which of the following statements about the Na-K pump is false?

Accepted Answer

It is located on the apical membrane of cell

Answer

It is not directly involved in the generation of action potentials.

Answer

It is electrogenic

Answer

It needs ATP for its functioning

Question 7

Cell-to-cell permeability occurs through

Accepted Answer

Connexins

Answer

Occludin

Answer

Zona adherens

Answer

Zonulin

Question 8

Which of the following characteristics is shared by both active transport and facilitated diffusion?

Accepted Answer

Requires specific carrier proteins

Answer

Does not require energy input

Answer

Transports solute down concentration gradient

Answer

Transports solute against concentration gradient

Question 9

What is the process of translocation through pores in cell membranes?

Accepted Answer

Facilitated diffusion

Answer

Transcytosis

Answer

Endocytosis

Answer

Active transport

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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