Cell Membranes: Composition, Purpose, Permeability

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Questions and Answers

Given the inherent asymmetry of the plasma membrane, which of the following statements best encapsulates the functional consequence of this structural arrangement in the context of cellular signaling?

It facilitates the symmetrical presentation of glycosylated moieties, optimizing cell-cell adhesion and recognition processes equally on all cellular surfaces.
It modulates the uniform distribution of membrane-bound enzymes, thereby ensuring consistent catalytic activity irrespective of cellular location.
It equalizes the electrochemical gradient across the membrane, promoting uniform ion flux and mitigating polarized cellular responses.
It allows for the compartmentalization of signal transduction pathways, enabling differential responses to stimuli based on receptor localization and downstream effector availability. (correct)

Considering the glycocalyx's role in cellular interaction and the implications of its negative charge, which scenarios would most likely be affected by enzymatic removal of the glycocalyx?

Enhanced non-specific cell adhesion and increased endocytosis.
Reduced cell-cell repulsion and attenuated receptor-ligand affinity. (correct)
Diminished phagocytosis and increased exocytosis rates.
Unimpeded cell migration and accelerated immune recognition.

In the context of Fick's Law of Diffusion, if a novel synthetic lipid were engineered to increase membrane thickness by an order of magnitude while simultaneously reducing lipid solubility for a specific molecule by half, how would the diffusion rate of that molecule be affected, assuming all other variables remain constant?

The diffusion rate would increase by approximately twofold.
The diffusion rate would decrease by approximately fivefold.
The diffusion rate would decrease by approximately twentyfold. (correct)
The diffusion rate would remain unchanged due to compensatory effects.

Given the role of cholesterol in modulating membrane fluidity, how would a cell membrane respond to a sudden and drastic decrease in temperature if it were engineered to lack cholesterol?

The membrane would exhibit increased rigidity and phase transition, potentially leading to impaired function. (C) Signup and view all the answers

Considering the structural and functional diversity of membrane proteins, which biophysical method would be most appropriate for determining the dynamic changes in protein conformation and oligomeric state within a native cell membrane environment in situ?

Förster Resonance Energy Transfer (FRET) microscopy, due to its sensitivity to distance changes between fluorescently labeled proteins in living cells. (B) Signup and view all the answers

In the context of membrane transport mechanisms, if a researcher discovers a novel integral membrane protein that facilitates the movement of a specific molecule across the plasma membrane without ATP hydrolysis, yet the transport rate is significantly higher than predicted by Fick's Law alone, how would you classify this protein's transport mechanism?

Facilitated Diffusion via a Carrier Protein, due to its protein-mediated, energy-independent, and saturable transport characteristics. (C) Signup and view all the answers

Given a scenario where a cell's membrane potential is experimentally clamped at 0 mV, what impact would this have on the electrochemical gradient and subsequent movement of ions across the membrane?

It would abolish only the electrical component of the electrochemical gradient, while preserving the chemical component, potentially leading to ion flux based solely on concentration differences. (A) Signup and view all the answers

How would artificially increasing the expression of aquaporin channels in a cell membrane affect the cell's response to osmotic stress induced by exposure to a hypertonic solution?

It would exacerbate cellular shrinkage due to accelerated water efflux down the osmotic gradient. (A) Signup and view all the answers

Considering the mechanism of the $Na^+/K^+$ ATPase pump, predict the immediate consequences of selectively inhibiting its dephosphorylation step using a non-hydrolyzable phosphate analog?

The pump would become locked in the $E_2-P$ conformation, preventing $K^+$ binding and subsequent ion translocation. (D) Signup and view all the answers

If a cell were engineered to express a constitutively active (always 'on') G protein-coupled receptor (GPCR) that signals via the cAMP pathway, what long-term cellular adaptations would most likely occur to counteract the chronic overstimulation?

Upregulation of phosphodiesterase (PDE) expression, downregulation of adenylyl cyclase expression and increased receptor endocytosis. (A) Signup and view all the answers

In the context of receptor-mediated endocytosis, if a cell were genetically modified to lack functional clathrin protein, predict the most immediate downstream effect on cellular uptake of transferrin.

Transferrin receptors would cluster diffusely on the cell surface, but the initiation of endocytic vesicles would be impaired, significantly reducing transferrin uptake. (A) Signup and view all the answers

A researcher discovers a novel ligand that binds to a cell surface receptor. Upon binding, the receptor activates a cascade that ultimately leads to increased gene expression in the nucleus. Knowing that the ligand itself does not enter the cell, which of the following mechanisms would most accurately describe the signal transduction pathway involved?

The receptor activates a series of intracellular second messengers that amplify the signal and ultimately regulate transcription factors. (C) Signup and view all the answers

In a hypothetical scenario, a researcher synthesizes a novel amphipathic molecule that spontaneously inserts into cell membranes, disrupting lipid packing and creating 'leaky' patches. How would this affect ion gradients and cellular homeostasis?

Intracellular ion concentrations would equilibrate with the extracellular environment, disrupting cellular processes. (D) Signup and view all the answers

Given that lipid rafts are enriched in cholesterol and sphingolipids, what biophysical technique would be most suitable to evaluate the lateral diffusion and dynamic behavior of a GPI-anchored protein within these specialized membrane domains?

Fluorescence Recovery After Photobleaching (FRAP) microscopy, for measuring the rate of protein diffusion within the membrane. (B) Signup and view all the answers

If a researcher discovers that a particular genetic mutation results in the production of a transmembrane protein with a significantly shortened intracellular domain, how might this affect signal transduction processes initiated by that receptor?

It would disrupt interactions with intracellular signaling molecules, potentially leading to impaired or altered downstream responses. (B) Signup and view all the answers

Considering the differences between channel and carrier proteins, what would be the predicted outcome of introducing a mutation that causes a carrier protein to form a continuous, water-filled pore through the membrane?

The protein would lose its specificity and selectivity, acting as a channel for various molecules. (B) Signup and view all the answers

If a lipid-soluble signaling molecule were designed to have a high affinity for both membrane and intracellular receptors, which cellular responses would be expected?

A combination of rapid changes in membrane excitability and long-term changes in protein synthesis. (A) Signup and view all the answers

How would a point mutation in the ligand-binding domain of a receptor tyrosine kinase (RTK) that prevents its dimerization affect downstream signaling pathways?

It would prevent receptor autophosphorylation and subsequent activation of downstream signaling cascades. (D) Signup and view all the answers

Given the complexity of cellular signaling networks, what experimental approach would be most effective in elucidating the specific interactions and temporal dynamics of protein complexes formed during signal transduction events?

Co-immunoprecipitation followed by mass spectrometry, due to its capacity identify interacting proteins under specific conditions. (A) Signup and view all the answers

How does the stoichiometry of ion binding sites on a ligand-gated ion channel affect the channel's response to varying concentrations of its ligand?

A higher stoichiometry results in a lower EC50, indicating increased sensitivity to the ligand. (A) Signup and view all the answers

If a cell were treated with a drug that selectively disrupts the interaction between G protein subunits and the receptor, which downstream signaling events would be most immediately affected?

Activation of adenylyl cyclase and subsequent cAMP production. (B) Signup and view all the answers

A researcher discovers a novel mutation in the gene encoding connexin proteins, resulting in the formation of gap junctions with significantly reduced pore size. How would this altered pore size most directly impact intercellular communication?

It would selectively permit the exchange of small signaling molecules while blocking the transfer of larger metabolites and ions. (A) Signup and view all the answers

If the extracellular concentration of $Na^+$ ions is suddenly reduced to near zero, how would this affect the secondary active transport of glucose into intestinal epithelial cells via SGLT1 transporters?

Glucose transport would cease entirely due to the collapse of the $Na^+$ electrochemical gradient. (D) Signup and view all the answers

If a cell were engineered to express a non-functional version of dynamin protein, what cellular process would be most directly impaired?

The budding and scission of vesicles from the plasma membrane during endocytosis. (B) Signup and view all the answers

In electrophysiology, how would the introduction of a non-selective cation channel (permeable to both $Na^+$ and $K^+$) into the plasma membrane of a neuron at resting membrane potential affect the membrane potential?

The membrane potential would depolarize due to increased $Na^+$ influx. (B) Signup and view all the answers

Given the properties of voltage-gated ion channels, how would a mutation that shifts the voltage-dependence of channel activation to more negative potentials affect neuronal excitability?

It would promote spontaneous action potential firing, increasing neuronal excitability. (A) Signup and view all the answers

In the scenario where intracellular chloride concentration is experimentally increased above its normal equilibrium potential in a neuron, how would the activation of GABA-A receptors affect the membrane potential?

GABA-A receptor activation would cause membrane depolarization due to Cl- efflux. (A) Signup and view all the answers

In the context of long-term potentiation (LTP) at glutamatergic synapses, how would selectively blocking the insertion of AMPA receptors into the postsynaptic membrane affect synaptic plasticity?

It would prevent LTP by blocking the increase in postsynaptic responsiveness to glutamate. (C) Signup and view all the answers

If a researcher designs a drug that selectively inhibits the activity of phosphodiesterases (PDEs) in neurons, how would this affect synaptic transmission mediated by G protein-coupled receptors (GPCRs) that signal through cAMP?

It would enhance synaptic transmission by prolonging the duration of cAMP signaling. (A) Signup and view all the answers

Given the complexity of membrane dynamics and cellular signaling, what theoretical framework provides the most comprehensive approach to understanding the emergent properties arising from the interactions of multiple components within the cell membrane?

Systems biology and network analysis, due to their ability to model complex interactions and predict emergent behaviors. (C) Signup and view all the answers

If the activity of the $Na^+/K^+$ ATPase pump were completely inhibited in a neuron, what would be the long-term consequences for the neuron's ability to maintain its resting membrane potential and generate action potentials?

The neuron would gradually depolarize, eventually becoming unable to generate action potentials due to the dissipation of ion gradients. (D) Signup and view all the answers

How would altering the lipid composition of a cell membrane to incorporate a higher proportion of unsaturated fatty acids affect the kinetics of integral membrane protein function, particularly those involved in signal transduction?

It would increase membrane fluidity, potentially affecting protein conformation, diffusion, and interaction with other signaling molecules, thus affecting signal-transduction efficiency. (C) Signup and view all the answers

Given that the phospholipid bilayer is impermeable to ions, how can the cell membrane potential change rapidly in response to a stimulus?

Ions utilize integral membrane proteins, such as ion channels, to traverse the membrane. (B) Signup and view all the answers

If a researcher discovers a novel compound that selectively inhibits the function of caveolin proteins, how would this affect caveolae-mediated endocytosis and potocytosis?

It would impair caveolae formation and endocytosis by disrupting the structural integrity of caveolae. (A) Signup and view all the answers

In the scenario where a neuron is exposed to a toxin that selectively blocks voltage-gated potassium channels, how would this affect the repolarization phase of the action potential?

The repolarization phase would be prolonged or absent, leading to extended depolarization. (A) Signup and view all the answers

Given the role of the ER in protein synthesis, which of the following is not correct about the RER?

RER can synthesize lipids and steroids. (A) Signup and view all the answers

If a hypothetical molecule with a molecular weight of 600 Daltons and a partition coefficient of 0.8 (octanol/water) is introduced into a cell, by which transport mechanism is it most likely to cross the cell membrane?

Simple Diffusion (D) Signup and view all the answers

Flashcards

Cell membrane

A thin, elastic structure, 7.5-10 nanometers thick, primarily composed of a sheet of lipid (fat) material, phospholipids and cholesterol, with interspersed proteins.

Phospholipids

The most abundant lipid in all membranes, forming a double layer with hydrophilic heads facing outwards and hydrophobic tails inwards.