Cellular Physiology Practice Questions

Q: Glucose is usually transported by:

Facilitated diffusion.. ***Facilitated diffusion*** - **Facilitated diffusion** is the primary mechanism for glucose uptake into most cells, especially down its concentration gradient, via specific **carrier proteins** (e.g., GLUT transporters). - This process does not require direct energy expenditure, as glucose moves from an area of higher concentration to lower concentration, but it still needs the help of a **membrane protein**. *Secondary active transport* - **Secondary active transport** of glucose (e.g., SGLT1 in the intestine and kidneys) involves the co-transport of glucose with Na+ ions, using the electrochemical gradient of Na+ as an energy source. - While important in specific locations for glucose absorption against a concentration gradient, it is not the general or "usual" transport mechanism for glucose into most other cells. *Simple diffusion* - **Simple diffusion** involves the passive movement of substances across a membrane directly, without the help of membrane proteins or energy. - Glucose molecules are too large and polar to cross the lipid bilayer directly via simple diffusion at physiologically significant rates. *Primary active transport* - **Primary active transport** directly uses energy from ATP hydrolysis to move substances against their concentration gradient, for example, the Na+/K+ ATPase. - Glucose transport itself does not typically involve direct ATP hydrolysis for movement across the cell membrane under normal physiological conditions in most cells.

Q: Neutral molecules are transported by:

Simple diffusion. ***Simple diffusion*** - **Neutral molecules** are typically **lipid-soluble** and can directly pass through the lipid bilayer of the cell membrane. - This process does not require **energy** or specialized **transporters** and occurs down a concentration gradient. *Ionophores* - **Ionophores** are organic molecules that increase the permeability of membranes to specific **ions**, not neutral molecules. - They act by either forming **channels** or by directly binding and ferrying ions across the membrane. *Porin channels* - **Porin channels** are primarily found in the outer membranes of **gram-negative bacteria** and **mitochondria**. - They facilitate the passage of small **hydrophilic molecules**, which can be charged or uncharged, but their primary role is not for the transport of neutral molecules via simple diffusion. *None of the options* - This option is incorrect because **simple diffusion** is a well-established mechanism for the transport of neutral molecules.

Q: Which is the most diffusible ion across the cell membrane?

K+. ***K+*** - The cell membrane is significantly more **permeable to potassium ions (K+)** than to other ions due to the presence of numerous **leak potassium channels**. - This higher permeability allows K+ ions to move more freely across the membrane, contributing significantly to the **resting membrane potential**. *Ca2+* - **Calcium ion (Ca2+)** permeability is generally very low in resting cells, with tightly regulated transport systems to maintain steep concentration gradients. - While essential for signaling, its diffusibility across the membrane is not the highest. *Cl-* - **Chloride ions (Cl-)** can diffuse across the membrane, but their permeability is typically lower than that of K+ in most resting cells. - Cl- movement often contributes to **hyperpolarization** or stabilization of the membrane potential. *Na+* - The cell membrane has relatively **low permeability to sodium ions (Na+)** in a resting state, as reflected by the action of the **Na+/K+ ATPase pump** actively pumping Na+ out of the cell. - While Na+ influx is crucial for **depolarization** during action potentials, its basal diffusibility is less than K+.

Q: Receptor mediated endocytosis is by

Clathrin. ***Clathrin*** - **Clathrin-mediated endocytosis** is the primary mechanism for **receptor-mediated endocytosis**. - **Clathrin** forms a characteristic **triskelion structure** that assembles into a polyhedral cage around the forming vesicle, facilitating the uptake of specific molecules. *Porin* - **Porins** are **beta-barrel proteins** that form pores in the outer membranes of gram-negative bacteria, mitochondria, and chloroplasts. - They are involved in the **passive diffusion** of small molecules and ions, not receptor-mediated endocytosis. *Oxytocin* - **Oxytocin** is a **peptide hormone** produced in the hypothalamus and released by the posterior pituitary. - It plays roles in **social bonding**, childbirth, and lactation, and is not involved in endocytosis. *Vimentin* - **Vimentin** is an **intermediate filament protein** found in various cell types, especially mesenchymal cells. - It provides structural support to the cell and is involved in cell migration and signaling, not the process of endocytosis.

Q: Which of the following is true regarding the Na+-K+ pump?

Pumps 3 Na+ out and 2 K+ in. ***Pumps 3 Na+ out and 2 K+ in*** - The **Na+-K+ pump (Na+/K+-ATPase)** is an active transporter that maintains the electrochemical gradients across the cell membrane. - For every molecule of **ATP** hydrolyzed, it expels **three sodium ions (Na+)** out of the cell and brings **two potassium ions (K+)** into the cell. *Pumps 2 Na+ out and 3 K+ in* - This option incorrectly reverses the stoichiometry of Na+ and K+ ions. - The pump's function is to create a net change in charge, bringing in fewer positive ions than it expels. *Pumps 1 Na+ out and 2 K+ in* - This option incorrectly states the number of both sodium and potassium ions transported. - The pump's characteristic ratio for Na+ and K+ is 3:2. *Pumps 2 Na+ out and 1 K+ in* - This option also presents an incorrect stoichiometry for the ions pumped. - The physiological ratio of ions moved by the Na+-K+ pump is consistently 3 Na+ out and 2 K+ in.

Q: Equilibrium potential for an ion is calculated by:

Nernst Equation. ***Nernst Equation*** - The **Nernst equation** is used to calculate the **equilibrium potential** for a **single ion** across a semi-permeable membrane. - It considers the **charge of the ion**, the **temperature**, and the **concentration gradient** of the ion across the membrane. *Gibbs Donnan Equilibrium* - The **Gibbs-Donnan equilibrium** describes the distribution of **permeable ions** when there is a **non-permeable charged molecule** on one side of a membrane. - It focuses on the **overall distribution of ions** and water, rather than the equilibrium potential of a *single* ion. *Goldman Equation* - The **Goldman-Hodgkin-Katz (GHK) equation**, often referred to as the **Goldman equation**, calculates the **resting membrane potential** of a cell. - It accounts for the **permeability and concentration gradients** of *multiple* ions (e.g., Na+, K+, Cl-) that contribute to the membrane potential. *None of the options* - This option is incorrect because the **Nernst Equation** is specifically designed for calculating the equilibrium potential of a single ion.

Q: Equilibrium potential of calcium is

+130mV. ***+130mV*** - The **equilibrium potential** for an ion is the **membrane potential** at which the net movement of that ion across the membrane is zero, even if there is a concentration gradient. - Due to the significantly higher extracellular concentration of **calcium ions (Ca2+)** relative to the intracellular concentration, a large positive membrane potential is required to prevent Ca2+ influx. *-32mV* - This value does not represent the typical **equilibrium potential** for any major physiological ion like sodium, potassium, chloride, or calcium in mammalian cells. - Equilibrium potentials are highly dependent on the **concentration gradients** of the specific ion. *+65mV* - This value is close to the typical **equilibrium potential for sodium (Na+)**, which is approximately +60 to +70 mV in many cells, due to its outward concentration gradient. - **Calcium's equilibrium potential** is much more positive than sodium's due to its larger concentration gradient and its divalent charge. *-95mV* - This value is close to the typical **equilibrium potential for potassium (K+)**, which is approximately -90 to -95 mV, reflecting the movement of potassium out of the cell. - The **equilibrium potential for calcium** is highly positive, whereas this negative value suggests an inward current for a positively charged ion.

Q: Which of the following is used for sex chromatin testing?

Barr body. ***Barr body*** - The **Barr body**, or sex chromatin, is an inactivated X chromosome found in the somatic cells of females. - Its presence or absence is used in sex chromatin testing to determine the number of X chromosomes. *Testosterone receptors* - **Testosterone receptors** are involved in mediating the effects of androgens and are not directly used for sex chromatin testing. - Abnormalities in these receptors can lead to conditions like **androgen insensitivity syndrome**, but they don't assess X chromosome number. *Phenotypic features* - While **phenotypic features** (visible characteristics) can suggest a person's sex or potential chromosomal abnormalities, they do not directly provide information about sex chromatin. - Definitive diagnosis requires **cytogenetic** or genetic testing. *Hormone levels* - **Hormone levels** (e.g., testosterone, estrogen) can indicate endocrine function but are not used to directly assess sex chromatin. - They reflect the activity of the gonads rather than the presence of inactivated X chromosomes.

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.

Question 1

Glucose is usually transported by:

Accepted Answer

Facilitated diffusion.

Answer

Secondary active transport.

Answer

Simple diffusion.

Answer

Primary active transport.

Question 2

Neutral molecules are transported by:

Accepted Answer

Simple diffusion

Answer

Ionophores

Answer

Porin channels

Answer

None of the options

Question 3

Which is the most diffusible ion across the cell membrane?

Accepted Answer

K+

Answer

Ca2+

Answer

Cl-

Answer

Na+

Question 4

Receptor mediated endocytosis is by

Accepted Answer

Clathrin

Answer

Porin

Answer

Oxytocin

Answer

Vimentin

Question 5

Which of the following is true regarding the Na+-K+ pump?

Accepted Answer

Pumps 3 Na+ out and 2 K+ in

Answer

Pumps 2 Na+ out and 3 K+ in

Answer

Pumps 1 Na+ out and 2 K+ in

Answer

Pumps 2 Na+ out and 1 K+ in

Question 6

Equilibrium potential for an ion is calculated by:

Accepted Answer

Nernst Equation

Answer

Gibbs Donnan Equilibrium

Answer

Goldman Equation

Answer

None of the options

Question 7

Equilibrium potential of calcium is

Accepted Answer

+130mV

Answer

-32mV

Answer

+65mV

Answer

-95mV

Question 8

Which of the following is used for sex chromatin testing?

Accepted Answer

Barr body

Answer

Testosterone receptors

Answer

Phenotypic features

Answer

Hormone levels

Question 9

Which cellular mechanism is predominantly affected by hyperkalemia?

Accepted Answer

Membrane depolarization

Answer

Membrane hyperpolarization

Answer

Intracellular protein synthesis

Answer

Cellular osmolarity

Question 10

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

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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