Plasma Membrane Permeability and Transport
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Questions and Answers

What is the primary conformational change induced by phosphorylation in the Ca²⁺ pump?

  • Inhibition of ATP binding to prevent further Ca²⁺ transport
  • Shift to the E1 conformation, promoting Ca²⁺ binding from the cytosol
  • Shift to the E2 conformation, enabling the transport of Ca²⁺ back into the SR (correct)
  • Release of Ca²⁺ ions into the cytosol

The Na⁺/K⁺-ATPase pump transports three K⁺ ions out of the cell and two Na⁺ ions into the cell.

False (B)

What type of ion do V-class ATPases specifically transport?

H⁺ ions (protons)

In the Na⁺/K⁺-ATPase pump mechanism, ATP is hydrolyzed to ADP, and a phosphate (P) is transferred to a conserved ______ residue on the α-subunit.

<p>Asp</p> Signup and view all the answers

What is the electrogenic effect of the Na⁺/K⁺-ATPase pump primarily contribute to?

<p>Creating an electrical potential across the cell membrane (A)</p> Signup and view all the answers

Which of the following is NOT a characteristic of AQP1?

<p>Involved in ATP synthesis. (A)</p> Signup and view all the answers

Match the following locations with the approximate pH maintained by V-class ATPases:

<p>Lysosomal lumen = pH 4.5-5.0 Cytosol = pH 7.0</p> Signup and view all the answers

V-class pumps are primarily found in the plasma membrane and pump sodium ions ($Na^+$) to establish a voltage gradient.

<p>False (B)</p> Signup and view all the answers

Which step in the Na⁺/K⁺-ATPase pump mechanism directly leads to the release of Na⁺ ions outside the cell?

<p>Conformational change after phosphorylation (A)</p> Signup and view all the answers

What is the key feature that distinguishes P-class pumps from other ATP-powered transport proteins?

<p>P-class pumps catalyze autophosphorylation of a key conserved Aspartate (Asp) residue during the transport cycle.</p> Signup and view all the answers

V-class ATPases acidify the lumen of the Golgi apparatus.

<p>False (B)</p> Signup and view all the answers

During muscle relaxation, the _______ in the SR membrane pumps $Ca^{2+}$ from the cytosol back into the SR.

<p>Ca²⁺-ATPase</p> Signup and view all the answers

Match the following classes of ATP-powered transport proteins with their primary function:

<p>P-class pumps = Transport ions across membranes, autophosphorylation V-class pumps = Pump protons into vacuoles, establishing acidic environments F-class pumps = Proton pumping and ATP synthesis ABC superfamily = Transport a wide range of molecules using ATP binding and hydrolysis</p> Signup and view all the answers

What conformational change occurs in the $Ca^{2+}$-ATPase during its transport cycle that allows it to bind $Ca^{2+}$ ions?

<p>The enzyme shifts from the $E_2$ to the $E_1$ conformation. (D)</p> Signup and view all the answers

In contracting skeletal muscle cells, the concentration of $Ca^{2+}$ in the cytosol is approximately 100 nM.

<p>False (B)</p> Signup and view all the answers

What is the role of the Asp~P bond in the $Ca^{2+}$-ATPase mechanism, and what type of bond is it?

<p>The Asp~P bond represents a high-energy acyl phosphate intermediate that facilitates conformational changes necessary for $Ca^{2+}$ transport.</p> Signup and view all the answers

What is the primary mechanism by which GLUT1 transporters facilitate glucose movement across the plasma membrane?

<p>Facilitated diffusion involving conformational changes of the transporter. (D)</p> Signup and view all the answers

The concentration of Na+ is typically higher inside the cytosol of animal cells compared to the extracellular fluid.

<p>False (B)</p> Signup and view all the answers

What type of transporter moves two different substances in opposite directions across a membrane?

<p>antiporter</p> Signup and view all the answers

Proteins that facilitate water transport across cell membranes are called ______.

<p>aquaporins</p> Signup and view all the answers

Which of the following molecules can readily diffuse across a pure phospholipid bilayer?

<p>Gases like $CO_2$ and $O_2$ (D)</p> Signup and view all the answers

Match each type of membrane transport protein with its corresponding function:

<p>Uniporter = Transports a single type of molecule across the membrane Symporter = Transports two different molecules simultaneously in the same direction Antiporter = Transports two different molecules in opposite directions Ion Channel = Allows ions to diffuse rapidly down their electrochemical gradient</p> Signup and view all the answers

If frog oocytes are microinjected with aquaporin mRNA and then placed in a hypotonic solution, what is the expected outcome?

<p>The oocytes will swell and burst due to increased water influx. (B)</p> Signup and view all the answers

Besides simple diffusion, facilitated diffusion, and filtration, what is another main type of passive transport?

<p>osmosis</p> Signup and view all the answers

How do V-class pumps differ from F-class pumps in terms of function?

<p>V-class pumps use ATP to pump protons, while F-class pumps generate ATP by pumping protons. (C)</p> Signup and view all the answers

If an organelle contains only V-class pumps, the pumping of H⁺ ions will lead to a significant change in intraluminal pH.

<p>False (B)</p> Signup and view all the answers

What are the two main types of domains that compose an ABC transporter?

<p>transmembrane (T) domains and ATP-binding (A) domains</p> Signup and view all the answers

The CFTR chloride channel is typically ______ under normal conditions.

<p>closed</p> Signup and view all the answers

Match the following characteristics with the appropriate pump or transporter:

<p>F-class pump = Generates ATP by pumping protons V-class pump = Uses ATP to pump protons CFTR transporter = Functions as an ATP-gated chloride channel Bacterial Permeases = Imports nutrients from the environment</p> Signup and view all the answers

What triggers the opening of the CFTR chloride channel?

<p>Phosphorylation of the R domain by a protein kinase and binding of two ATP molecules to the A domains. (C)</p> Signup and view all the answers

The electrical potential generated by V-class pumps will be negligible if chloride ions passively follow the pumped H⁺ ions.

<p>True (A)</p> Signup and view all the answers

In addition to the transmembrane and ATP-binding domains, what additional domain is present in the CFTR protein structure?

<p>R domain</p> Signup and view all the answers

What structural feature of a potassium channel allows it to selectively bind K+ ions over Na+ ions?

<p>Backbone carbonyl oxygens in the P segment that coordinate with dehydrated K+ ions. (D)</p> Signup and view all the answers

In patch-clamp experiments, a strong suction is used to ensure the patch electrode is tightly sealed to the plasma membrane.

<p>False (B)</p> Signup and view all the answers

What is the function of the two-Na+/one-glucose symporter, and in which types of cells is it commonly found?

<p>The two-Na+/one-glucose symporter is found in cells such as those in the small intestine and kidney tubules, and functions to import glucose against its concentration gradient by coupling it with the import of two Na+ ions.</p> Signup and view all the answers

The enzyme __________ catalyzes the conversion of CO2 and H2O into bicarbonate and H+ in osteoclasts.

<p>carbonic anhydrase</p> Signup and view all the answers

Match the process with its primary function:

<p>Ion selectivity filter = Selects for K+ ions using backbone carbonyl oxygens Patch clamping = Measures single ion channel activity. Two-Na+/one-glucose symporter = Imports glucose against its concentration gradient. V-class Proton Pump = Pumps H+ into the extracellular space during bone resorption.</p> Signup and view all the answers

During bone resorption by osteoclasts, what is the role of the ClC-7 chloride channel?

<p>To facilitate Cl- diffusion to maintain electroneutrality in the extracellular space. (C)</p> Signup and view all the answers

Which of the following is a direct result of the binding of Na+ and glucose to the two-Na+/one-glucose symporter?

<p>A conformational change that temporarily occludes the substrates. (D)</p> Signup and view all the answers

The dissolution of bone by osteoclasts is primarily for removing calcium from bone to regulate blood calcium levels.

<p>False (B)</p> Signup and view all the answers

Flashcards

Conformational change

A structural shift in a protein due to phosphorylation that aidsCa²⁺ transport.

Dephosphorylation

The removal of a phosphate group, restoring the original conformation of a protein.

Na⁺ binding

The first step where three Na⁺ ions attach to the Na+/K+ ATPase pump.

ATP hydrolysis

The breakdown of ATP into ADP and phosphate, triggering a conformational change in the pump.

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Ion exchange in Na+/K+ ATPase

The pump moves three Na⁺ ions out and two K⁺ ions in for cellular balance.

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Electrogenic effect

The effect of charge separation created by the Na+/K+ pump, affecting membrane potential.

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V-Class ATPase

Pumps that specifically transport H⁺ ions to acidify cellular compartments.

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Proton gradient maintenance

The ability of V-Class ATPases to maintain a large difference in proton concentration across membranes.

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AQP1

A channel protein that transports 3x10^9 water molecules per second, impermeable to ions.

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P-class pumps

Transport ions using ATP, key feature is autophosphorylation of conserved aspartate.

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V-class pumps

Found in vacuolar membranes, primarily pump protons (H⁺) into organelles.

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F-class pumps

Present in mitochondria and chloroplasts, pump protons and synthesize ATP using gradients.

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ABC superfamily

A group of transport proteins utilizing ATP for transporting a variety of molecules without forming phosphorylated intermediates.

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Sarcoplasmic reticulum (SR)

Storage site for Ca²⁺ ions in skeletal muscle cells, high concentration compared to cytosol.

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Muscle contraction mechanism

Ca²⁺ release from SR into cytosol causes contraction; relaxing involves pumping Ca²⁺ back into SR.

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Ca²⁺-ATPase function

P-Class pump in SR that binds Ca²⁺ and uses ATP to return calcium to SR after muscle contraction.

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Membrane potential

The voltage difference created by ion movement across a membrane, affecting cellular function.

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Effect of V-class pumps on pH

V-class pumps create an electrical potential without altering intraluminal pH significantly.

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ABC Transporters

Proteins using ATP to transport various substances across membranes, featuring two T and two A domains.

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CFTR function

An ABC transporter ion channel that reabsorbs chloride ions, critical for sweat regulation.

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CFTR structure

Contains two transmembrane domains, two ATP-binding domains, and an additional regulatory domain (R).

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CFTR channel regulation

CFTR is usually closed; opens through PKA phosphorylation and ATP binding.

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Plasma membrane permeability

The ability of substances to cross the plasma membrane.

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Na+ concentration in cytosol

Sodium ion concentration inside the cell is 10 times lower than in extracellular fluid.

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Proton concentration in lysosome

Proton concentration inside lysosomes is about 100 times higher.

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Facilitated diffusion

Passive transport through a membrane involving transport proteins.

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Aquaporins

Water-selective channels that facilitate rapid water transport across membranes.

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Uniporters

Transporters that move a single substance across the membrane.

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Symporters

Transporters that move two different substances in the same direction.

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Osmosis

The spontaneous movement of water through a selectively permeable membrane.

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Ion Selectivity

The ability of ion channels to preferentially allow specific ions to pass, such as K+ over Na+.

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P Segment

Part of the ion channel pore that forms the ion-selectivity filter, utilizing carbonyl oxygens for K+ coordination.

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K+ Coordination

K+ ions lose water molecules and coordinate with 8 carbonyl oxygens from the P segment's backbone.

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Na+ Ion Challenge

Na+ ions struggle to perfectly coordinate with the channel’s oxygen due to their water shell, so pass rarely.

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Patch Clamping

A technique for measuring the activity of individual ion channels by using a patch electrode to isolate and record current.

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Two-Na+/one-glucose symporter

A transport protein that imports glucose alongside two Na+ ions, working against glucose's concentration gradient.

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Osteoclast Function

Cells responsible for dissolving bone during remodeling, aiding in repair of damaged bones.

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V-class Proton Pump

Pumps H+ ions into the extracellular space created by polarized osteoclasts, aiding in bone dissolution.

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Study Notes

Plasma Membrane Permeability

  • Extracellular fluid NaCl concentration in animals is >150 mM
  • Na+ concentration in cytosol is tenfold lower than extracellular fluid
  • K+ concentration in cytosol is higher than extracellular fluid
  • Proton concentration in lysosomes is 100-fold greater than extracellular fluid
  • Only small, uncharged, and water-soluble molecules readily diffuse across phospholipid bilayer (e.g., CO2, N2, O2, ethanol, water, urea)

Membrane Transport Proteins

  • ATP-powered pumps: Move ions against concentration gradients, using ATP (e.g., 100–103 ions/s for pumps, 107–108 ions/s for channels).
  • Ion channels: Allow rapid ion movement (e.g., aquaporins)
  • Transporters: Move one substance (uniporters), two in same direction (symporters), or two in opposite directions (antiporters)

Groups of Transporters

  • Uniporters: Move one substance at a time (e.g., GLUT1, glucose transporter)
  • Symporters: Move two substances in the same direction (e.g., Na+/glucose symporter)
  • Antiporters: Move two substances in opposite directions (e.g., Na+/proton antiporter)

GLUT1 Transport

  • Glucose binding to outward-facing site causes conformational change
  • Binding site now faces cytosol, and glucose is released into cell
  • Transporter returns to outward-facing conformation

Osmotic Pressure

  • Osmosis is a type of passive transport (other two types: simple diffusion, facilitated diffusion, filtration)
  • Water moves from high to low water potential

Aquaporin

  • Water-selective channels that increase water permeability in cell membranes
  • Expression increases water permeability in frog oocytes
  • Frog oocytes injected with aquaporin mRNA swell and burst in hypotonic solutions, suggesting water-channel function.
  • AQP1 can transport 3 x 10^9 water molecules per subunit per second
  • Impermeable to ions
  • Can transport water, glycerol, and urea

P-Class Pumps

  • Transport ions across membranes (e.g., Na+/K+ ATPase, Ca2+ ATPase)
  • Active transport, using ATP to move ions against concentration gradients
  • Catalyze autophosphorylation of an Asp residue

V-Class Pumps

  • Found in vacuolar membranes (e.g., lysosomes, endosomes)
  • Pump protons (H+) into vacuoles or organelles, establishing acidic environments
  • Do not involve phosphorylation

F-Class Pumps

  • Found in mitochondria, chloroplasts, and bacterial membranes (e.g., ATP synthase)
  • Function in proton pumping and ATP synthesis.
  • Reversible: can synthesize ATP using proton gradient

ABC Superfamily

  • Transport a wide range of molecules (ions, lipids, drugs)
  • Includes MDR proteins
  • Use ATP binding and hydrolysis to transport molecules, without forming a phosphorylated intermediate

Ca2+ in Skeletal Muscle Cells

  • Storage: Ca2+ ions are concentrated in the sarcoplasmic reticulum (SR).

Muscle Contraction and Relaxation

  • Contraction: Ca2+ release from SR causes contraction
  • Relaxation: Ca2+-ATPase pumps Ca2+ back into SR

Ca2+-ATPase Mechanism

  • Located in SR membrane of skeletal muscle cells
  • Two Ca2+ binding sites face the cytosol initially
  • ATP binding and hydrolysis leads to phosphorylation and conformational change
  • Ca2+ is transported back into SR
  • Dephosphorylation returns to initial conformation

Na+/K+ ATPase Pump Mechanism

  • Na+ binding (3 Na+ ions)
  • ATP binding and hydrolysis
  • Phosphorylation
  • Conformational change
  • Na+ release
  • K+ binding (2 K+ ions)
  • Dephosphorylation
  • K+ release

V-Class ATPase Mechanism

  • Transport of H+ ions
  • Acidify lumen of lysosomes, endosomes, and plant vacuoles
  • Maintain steep H+ gradient across membranes

ABC Transporters

  • Use ATP to transport substances across membranes
  • Composed of two transmembrane (T) domains and two ATP-binding domains (A).
  • Bacterial permeases, multidrug resistance proteins

CFTR

  • Class: ABC transporter ion channel (not a pump); conducts chloride ions
  • Structure: Composed of two transmembrane (T) domains and two ATP-binding (A) domains and an R domain
  • Function: Crucial for reuptake of chloride ions lost during sweating. Opening triggered by phosphorylation of the R domain
  • Ion Selectivity: Filters K+ ions preferentially over Na+ (lose water molecules and become bound to the carbonyl oxygens)

Patch Clamping

  • Purpose: Measure ion channel activity
  • Method: Patch electrode applied to membrane; slight suction

Two-Na+/one-glucose symporter

  • Function: Import glucose against concentration gradient by coupling with Na+ import
  • Steps: Glucose and Na+ binding, conformational change, inward-facing conformation, dissociation, reversion

Dissolution of Bone by Osteoclasts

  • Function: Dissolve bone for remodeling
  • Process: Polarized osteoclasts form enclosed space; carbonic anhydrase converts CO2 and H2O to bicarbonate and H+; V-class proton pumps acidify space; Cl-/HCO3- antiporters maintain electroneutrality; outcome: acidified space dissolves bone

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BIOL 408 Ch. 11 Plasma Membrane Permeability PDF

Description

Explores plasma membrane permeability, highlighting ion concentrations and molecule diffusion. Covers ATP-powered pumps, ion channels, and transporters like uniporters, symporters, and antiporters. Focuses on mechanisms facilitating substance movement across the cell membrane.

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