Cell Membrane and Transport Quiz
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Questions and Answers

What is the primary function of the Na+-glucose cotransporter?

  • To use Na+ gradient to move glucose into the cell (correct)
  • To transport Na+ ions out of the cell
  • To generate ATP from glucose
  • To exchange K+ for Na+ ions
  • Which type of ion channel is specifically activated by changes in membrane potential?

  • Voltage-gated channel (correct)
  • Leak channel
  • Ligand-gated channel
  • Mechanosensitive channel
  • Which of the following statements about sodium channels is false?

  • They become inactivated shortly after opening.
  • They allow Na+ to flow out of the cell during depolarization. (correct)
  • They are inhibited by local anesthetics like lidocaine.
  • They play a critical role in the action potential of neurons.
  • What is the role of the Na+-Ca2+ exchanger?

    <p>It exports Na+ while importing Ca2+.</p> Signup and view all the answers

    What class of drugs can block voltage-sensitive calcium channels?

    <p>Calcium-channel blockers</p> Signup and view all the answers

    Which type of molecules can freely diffuse across the plasma membrane?

    <p>Lipid soluble molecules</p> Signup and view all the answers

    What primarily drives the movement of molecules across the plasma membrane?

    <p>Concentration gradients</p> Signup and view all the answers

    What does the term 'selectively permeable' refer to in the context of the plasma membrane?

    <p>It permits certain molecules while restricting others.</p> Signup and view all the answers

    What is the basis for the electrical excitability of nerve and muscle cells?

    <p>Membrane potential due to charge separation</p> Signup and view all the answers

    What role does membrane potential play in cells?

    <p>It assists in the transport of substances.</p> Signup and view all the answers

    What is the primary function of the plasma membrane?

    <p>To act as a barrier to free passage of substances</p> Signup and view all the answers

    Which type of transport mechanism does not require energy?

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

    What role does the Na+-K+ pump play in cells?

    <p>It helps maintain membrane potential</p> Signup and view all the answers

    Which of the following describes endocytosis?

    <p>The engulfing of substances into the cell</p> Signup and view all the answers

    What are the components of the cell membrane's phospholipid bilayer?

    <p>Two layers of phospholipids and proteins</p> Signup and view all the answers

    Which ion is primarily pumped out of the cell by the Na+-K+ pump?

    <p>Sodium (Na+)</p> Signup and view all the answers

    What types of molecules can easily diffuse across the plasma membrane?

    <p>Small lipid-soluble molecules</p> Signup and view all the answers

    What characteristic of membrane proteins allows them to perform their functions?

    <p>Their structure and shape</p> Signup and view all the answers

    What is the primary reason for the negative resting membrane potential inside the cell?

    <p>Unequal distribution of K+, Na+, and large protein anions</p> Signup and view all the answers

    How does the Na+/K+ ATPase pump contribute to the resting membrane potential?

    <p>It creates a concentration gradient of Na+ and K+</p> Signup and view all the answers

    What is the main ion responsible for generating the resting membrane potential?

    <p>K+</p> Signup and view all the answers

    What is the typical resting membrane potential value for a neuron?

    <p>-70 mV</p> Signup and view all the answers

    What effect does the selective permeability of the membrane to K+ ions have on the resting membrane potential?

    <p>It allows K+ to diffuse out, making the inside of the cell more negative</p> Signup and view all the answers

    What ions are transported by the sodium-potassium ATPase and in what direction?

    <p>Three Na+ ions out of the cell and two K+ ions into the cell</p> Signup and view all the answers

    Which statement correctly describes depolarisation?

    <p>It occurs when the membrane potential becomes more positive.</p> Signup and view all the answers

    What is hyperpolarisation?

    <p>An increase in the negativity of the membrane potential.</p> Signup and view all the answers

    What is the major driving force for transport processes across membranes?

    <p>Sodium-potassium ATPase activity</p> Signup and view all the answers

    Which of the following options indicates repolarisation?

    <p>Return of the membrane potential to resting state</p> Signup and view all the answers

    During which phase is the membrane potential the highest?

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

    What is the typical resting membrane potential of a cell?

    <p>-70 mV</p> Signup and view all the answers

    What is the effect of sodium ion influx on membrane potential?

    <p>It leads to depolarisation.</p> Signup and view all the answers

    What determines the direction of movement for lipid-soluble and small uncharged molecules across the plasma membrane?

    <p>The concentration gradient</p> Signup and view all the answers

    What phenomenon arises from the separation of opposite charges across the plasma membrane?

    <p>Membrane potential</p> Signup and view all the answers

    Which of the following accurately describes cells with membrane potentials?

    <p>All cells exhibit a membrane potential.</p> Signup and view all the answers

    How do excitable cells utilize membrane potential?

    <p>To induce electrical excitability</p> Signup and view all the answers

    What is the primary factor that prevents the free movement of charged ions and water-soluble substances across the plasma membrane?

    <p>The hydrophobic interior of the membrane</p> Signup and view all the answers

    What primarily maintains the unequal distribution of K+ and Na+ in and out of the cell?

    <p>Na+/K+ ATPase pump function</p> Signup and view all the answers

    What effect does the selective leakiness of the plasma membrane to K+ have on the resting membrane potential?

    <p>Contributes to a more negative interior</p> Signup and view all the answers

    How many sodium ions are transported out of the cell for every two potassium ions transported in by the Na+/K+ ATPase pump?

    <p>3 Na+ for 2 K+</p> Signup and view all the answers

    What ion concentration is highest inside the cell at resting membrane potential?

    <p>K+</p> Signup and view all the answers

    What results from the unequal transport of positive ions by the Na+/K+ ATPase pump?

    <p>A slight negative charge inside the cell</p> Signup and view all the answers

    What characterizes a membrane potential?

    <p>Difference in charge concentration between intra and extracellular environments</p> Signup and view all the answers

    What is the typical resting membrane potential value for a neuron?

    <p>-70 mV</p> Signup and view all the answers

    What causes the cell membrane to be more negative inside compared to outside?

    <p>Presence of negatively charged proteins inside the cell</p> Signup and view all the answers

    What indicates the presence of a membrane potential across a cell membrane?

    <p>Separation of charged ions creating a potential difference</p> Signup and view all the answers

    What is the significance of the separation of charges across the plasma membrane?

    <p>It generates a voltage potential necessary for cellular functions</p> Signup and view all the answers

    Which of the following is true regarding the conditions of a cell in the absence of a membrane potential?

    <p>Charged ions are uniformly distributed</p> Signup and view all the answers

    How does charge separation across the plasma membrane influence the physiological activities of the cell?

    <p>It allows for the generation of action potentials</p> Signup and view all the answers

    What term can be used to describe the interior of a neuron compared to its exterior at rest?

    <p>More negative in charge</p> Signup and view all the answers

    What primarily causes the inside of a cell to become negatively charged at rest?

    <p>The leakage of K+ ions out of the cell</p> Signup and view all the answers

    What is the significance of the Nernst equation in relation to K+ ions?

    <p>It reveals the equilibrium potential for K+ based on concentration gradients</p> Signup and view all the answers

    What is the role of residual negative charge in a cell regarding K+ ions?

    <p>It draws K+ ions back into the cell</p> Signup and view all the answers

    How does the concentration gradient for K+ ions differ between the extracellular fluid (ECF) and intracellular fluid (ICF)?

    <p>K+ concentration is significantly higher in the ICF than in the ECF</p> Signup and view all the answers

    What is the conventional resting membrane potential of a neuron?

    <p>-70 mV</p> Signup and view all the answers

    Which membrane components contribute to the negative inner membrane potential?

    <p>Phosphatidylinositol and phosphatidylserine</p> Signup and view all the answers

    What balances the electrical and chemical driving forces on K+ at equilibrium?

    <p>Electrical force balances chemical force, resulting in no net transport</p> Signup and view all the answers

    Which value is crucial for calculating the equilibrium potential for K+ using the Nernst equation?

    <p>The concentration ratio of K+ outside and inside the cell</p> Signup and view all the answers

    Which ion cannot cross the plasma membrane freely according to the provided data?

    <p>A-</p> Signup and view all the answers

    Which ions are pumped out of the cell by the sodium-potassium ATPase?

    <p>Three Na+ ions</p> Signup and view all the answers

    What change in membrane potential occurs during depolarization?

    <p>The potential becomes positive</p> Signup and view all the answers

    Which of the following best describes repolarization?

    <p>It stabilizes the resting membrane potential</p> Signup and view all the answers

    During the action of the sodium-potassium ATPase, how many potassium ions are transported into the cell?

    <p>Two K+ ions</p> Signup and view all the answers

    What is a primary effect of the sodium-potassium ATPase on cell function?

    <p>Formation of chemical gradients</p> Signup and view all the answers

    What does hyperpolarization indicate concerning membrane potential?

    <p>An increase in negative charge inside the cell</p> Signup and view all the answers

    What role does sodium play in the transport processes across cell membranes?

    <p>It drives the transport of other substances into the cell</p> Signup and view all the answers

    What is the typical electrical state of a cell at resting membrane potential?

    <p>Negative interior relative to outside</p> Signup and view all the answers

    What is the relationship between membrane potential and the distribution of ions across the plasma membrane?

    <p>Membrane potential depends on the difference in cation and anion concentrations across the membrane.</p> Signup and view all the answers

    How do excitable cells utilize membrane potential for their function?

    <p>By inducing changes in membrane potential for signal transmission.</p> Signup and view all the answers

    What is the primary factor that enables the selective permeability of the plasma membrane?

    <p>The hydrophobic interior that restricts the movement of charged and polar molecules.</p> Signup and view all the answers

    Why is the resting membrane potential typically negative in cells?

    <p>There is a higher concentration of anions inside the cell compared to outside.</p> Signup and view all the answers

    What role does charge separation across the plasma membrane play in cellular physiology?

    <p>It creates a basis for electrical excitability and signaling within nerve and muscle cells.</p> Signup and view all the answers

    What contributes to the generation of the resting membrane potential due to the unequal distribution of ions?

    <p>The selective permeability of the membrane to K+ ions</p> Signup and view all the answers

    What effect does the Na+/K+ ATPase pump have on the membrane potential of the cell?

    <p>It establishes concentration gradients for Na+ and K+</p> Signup and view all the answers

    During resting membrane potential, which ion's diffusion plays the most significant role in making the inside of the neuron negatively charged?

    <p>K+ moving out of the cell</p> Signup and view all the answers

    What is the purpose of the Na+/K+ ATPase in regards to cellular ion balance?

    <p>To establish an uneven distribution of Na+ and K+ across the plasma membrane</p> Signup and view all the answers

    What outcome results from the K+ ions diffusing out of the cell through the leaky plasma membrane?

    <p>A negative charge developing inside the cell relative to the outside</p> Signup and view all the answers

    What constitutes the primary barrier of the cell membrane which helps maintain distinct internal and external environments?

    <p>Phospholipid bilayer</p> Signup and view all the answers

    Which feature of membrane proteins allows them to function both as receptors and channels?

    <p>Their hydrophilic and hydrophobic regions</p> Signup and view all the answers

    How does the Na+-K+ pump primarily influence membrane potential?

    <p>By transporting more Na+ ions out of the cell than K+ ions into the cell</p> Signup and view all the answers

    Which mechanism represents the process of engulfing large particles by the cell membrane?

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

    Which type of transport mechanism does NOT involve the movement of molecules against their concentration gradient?

    <p>Facilitated diffusion</p> Signup and view all the answers

    What role does the fluidity of the plasma membrane play in cellular function?

    <p>It facilitates communication between neighboring cells</p> Signup and view all the answers

    Which statement best differentiates between active and passive transport mechanisms?

    <p>Active transport moves substances from low to high concentration, while passive transport moves them from high to low concentration</p> Signup and view all the answers

    What happens to the ion concentration inside a cell at resting membrane potential?

    <p>K+ concentration is higher than Na+ concentration</p> Signup and view all the answers

    What happens to the membrane potential in the presence of a membrane potential?

    <p>A charge difference is established across the membrane.</p> Signup and view all the answers

    Which statement accurately describes the state of a cell membrane in the absence of a membrane potential?

    <p>The extracellular and intracellular environments have equal ionic concentration.</p> Signup and view all the answers

    How is the typical resting membrane potential of a neuron characterized?

    <p>It is more negative inside the cell than outside, around -70 mV.</p> Signup and view all the answers

    What primarily contributes to the resting membrane potential being negative?

    <p>The active transport mechanisms of sodium-potassium ATPase pump.</p> Signup and view all the answers

    What is indicated by the presence of separated charged ions across the plasma membrane?

    <p>An electric potential difference exists across the membrane.</p> Signup and view all the answers

    Which of the following best describes the concept of membrane potential?

    <p>The condition resulting from the separation of electrically charged ions.</p> Signup and view all the answers

    Which consequence occurs due to the selective permeability of the plasma membrane to certain ions?

    <p>A resting membrane potential is established.</p> Signup and view all the answers

    What effect does the presence of positive ions inside the cell have on the membrane potential?

    <p>It contributes to the depolarization of the membrane.</p> Signup and view all the answers

    Which of the following is transported by the sodium-potassium ATPase?

    <p>Three Na+ ions out of the cell and two K+ ions into the cell</p> Signup and view all the answers

    What effect does depolarization have on the membrane potential?

    <p>It increases the membrane potential towards a more positive value</p> Signup and view all the answers

    How does hyperpolarization affect the state of the cell?

    <p>It raises the threshold for action potential generation</p> Signup and view all the answers

    Which statement best describes the function of cotransporters in relation to sodium ions?

    <p>Cotransporters utilize the sodium gradient to move substances into the cell</p> Signup and view all the answers

    What role does the resting membrane potential play in cellular activity?

    <p>It provides a baseline for excitability and responsiveness to stimuli</p> Signup and view all the answers

    What occurs during repolarization of the membrane potential?

    <p>There is a decrease in Na+ permeability and an increase in K+ permeability</p> Signup and view all the answers

    Which situation best describes a condition where the sodium-potassium ATPase is malfunctioning?

    <p>Increased Na+ intracellular concentration without any K+ alteration</p> Signup and view all the answers

    What is the typical response of a neuron following a significant depolarization event?

    <p>Initiation of an action potential if the threshold is reached</p> Signup and view all the answers

    Study Notes

    Cell Membrane

    • Plasma membrane surrounds all cells.
    • Functions: structural barrier, controls substance passage, maintains internal/external composition, contributes to cell fluidity, enables cell communication, and allows response to stimuli.
    • Two main components: phospholipid bilayer and proteins.

    Membrane Transport

    • Diffusion: Movement of molecules from high to low concentration (e.g., oxygen, carbon dioxide, fat-soluble substances).
    • Protein-mediated transport:
      • Channel proteins: act as selective pores for specific molecules.
      • Carrier proteins: bind to molecules and facilitate their movement across the membrane.
    • Endocytosis: engulfing substances from the extracellular environment.
      • Phagocytosis: engulfing solid particles.
      • Pinocytosis: engulfing liquids.
    • Exocytosis: releasing substances from within the cell to the extracellular environment.

    Membrane Potential

    • Membrane potential results from the separation of charges across the cell membrane.
    • All cells have a membrane potential, which is the electrical difference across the membrane.
    • Excitable cells (nerve and muscle) actively change their membrane potential, which is the basis for their electrical excitability.
    • Membrane potential is also used to transport substances.

    Resting Membrane Potential (RMP)

    • RMP is the potential difference maintained across the cell membrane when the cell is at rest.
    • RMP is usually negative inside the cell compared to the outside.
    • Neurons typically have an RMP of approximately -70 mV.
    • RMP is a result of two factors:
      • Unequal distribution of ions: K+ ions are higher inside the cell, Na+ ions are higher outside the cell, and large protein anions are only found inside the cell.
      • Selective permeability of the plasma membrane: the membrane is more permeable to K+ ions than Na+ ions.

    Na+/K+ ATPase (Pump)

    • This protein plays a crucial role in establishing and maintaining the concentration gradients of Na+ and K+ across the cell membrane.
    • It actively transports 3 Na+ ions out of the cell for every 2 K+ ions transported into the cell.
    • This process requires energy (ATP) and contributes to the negative charge inside the cell.

    Factors contributing to RMP

    • The Na+/K+ ATPase creates a small potential difference by transporting more positive charges out than in.
    • The key factor contributing to the RMP is the diffusion of K+ ions out of the cell down their concentration gradient. This movement leaves the inside of the cell more negative compared to the outside.

    Membrane Potential Changes

    • Depolarization: The membrane potential becomes more positive.
    • Hyperpolarization: The membrane potential becomes more negative.
    • Repolarization: The membrane potential returns to its resting state.

    Na+/K+ Pump and Transport Processes

    • The Na+/K+ pump provides the driving force for various transport processes across the membrane.
    • Cells utilize the Na+ concentration gradient created by the pump to drive other transport mechanisms.
    • Cotransporters: move substances in the same direction as Na+ (e.g., glucose, amino acids).
    • Exchangers: move substances in the opposite direction of Na+ (e.g., Ca2+, H+).

    Classes of Ion Channels

    • Leak channels: constantly open and allow ions to flow passively down their concentration gradients (e.g., K+ leak channels).
    • Voltage-gated channels: open and close in response to changes in membrane potential (e.g., voltage-gated sodium channels).
    • Ligand-gated channels: open and close in response to the binding of specific molecules (ligands) (e.g., acetylcholine receptor).

    Drug Modification of Ion Channels

    • Local anesthetics: block voltage-gated Na+ channels, leading to reduced nerve impulse transmission (e.g., Xylocaine/Lidocaine).
    • Ca2+-channel blockers: inhibit Ca2+ channels, affecting smooth muscle contraction and blood vessel constriction (e.g., nifedipine).

    Membrane Permeability

    • Lipid soluble and small uncharged molecules (e.g. oxygen) freely diffuse across cell membranes
    • Movement across the membrane is driven by the concentration gradient
    • Charged ions and water-soluble molecules cannot freely move across the hydrophobic interior of the cell membrane
    • Cell membranes are selectively permeable
    • The cell membrane is permeable to certain substances and impermeable to others

    Membrane Potential

    • Opposite charges attract and the separation of these creates a membrane potential
    • There is a difference in concentration of positive and negative ions across the cell membrane
    • All cells have a membrane potential
    • Excitation cells actively induce changes in the membrane potential
    • The membrane potential is the basis for the electrical excitability of nerve and muscle cells
    • Membrane potential can be harnessed for transporting substances

    Absence of a Membrane Potential

    • No charge difference across the membrane, resulting in no membrane potential

    Presence of a Membrane Potential

    • Separated charges are responsible for the presence of a membrane potential

    Resting Membrane Potential (RMP)

    • The cell membrane is more negative inside than outside
    • The RMP of a neuron is approximately -70mV
    • The unequal distribution of potassium, sodium, and protein anions (A-) between the inside and outside of the cell contributes to the RMP
    • The permeability of the cell membrane to potassium plays a major role
    • The cell membrane contains many leak channels, that allow potassium to diffuse out of the cell down its concentration gradient

    Concentration of Ions

    • The intracellular concentration of potassium is significantly higher than the extracellular concentration
    • Conversely, the extracellular concentration of sodium is significantly higher than the intracellular concentration
    • The concentration of protein anions (A-) is only found intracellularly

    Sodium-Potassium ATPase (Na-K Pump)

    • The Na-K pump is a membrane-spanning enzyme that establishes the concentration gradients of Na+ and K+
    • The pump transports three sodium ions out of the cell and two potassium ions into the cell
    • The pump uses ATP as an energy source
    • The pump actively transports approximately 200 million ions per second

    Contribution to RMP

    • The Na-K pump generates a small potential due to unequal transport of positive ions across the membrane
    • The inside of the cell becomes slightly negatively charged relative to the outside because of the 3Na+ out for 2K+ in ratio
    • Diffusion of potassium out of the cell down its concentration gradient contributes significantly to the RMP
    • Potassium leaks out of the cell down its concentration gradient, further increasing the negativity inside the cell

    Additional Contributors to Negative Membrane Potential

    • Phosphatidylinositol (PIP2) and Phosphatidylserine (PS) contribute to the negative inner membrane potential
    • These negatively charged lipids provide a negative charge to the inner part of the plasma membrane

    Nernst Equilibrium

    • The chemical gradient acts as the driving force for diffusion of potassium out of the cell
    • The chemical gradient is balanced by the electrical gradient which draws potassium back into the cell
    • At equilibrium, the electrical force balances the chemical force, resulting in no net transport of potassium

    Nernst Equation

    • The Nernst equation is used to calculate the equilibrium potential for an ion
    • The equilibrium potential is the membrane potential at which the electrical driving force for the ion movement is equal and opposite to the chemical driving force

    Membrane Potential Changes

    • Depolarization: The membrane potential becomes more positive
    • Hyperpolarization: The membrane potential becomes more negative
    • Repolarization: The membrane potential returns to its resting state

    NA-K Pump and Transport Processes

    • The cell utilizes the chemical gradient of sodium to transport substances into the cell
    • Cotransporters are involved in this process

    Cell Membrane

    • Plasma Membrane: 3-10 nm thick membrane made of fluid lipid-protein bilayer, enclosing all cells
    • Functions:
      • Structural barrier
      • Controls substance passage, maintaining cell's internal environment
      • Maintains cell fluidity
      • Facilitates communication between cells
      • Enables response to external stimuli
    • Membrane Proteins:
      • Integral/transmembrane: Span the entire membrane
      • Extrinsic/peripheral: Attached to the membrane surface

    Transport Across Membranes

    • Diffusion: Movement of substances across membrane driven by concentration gradient, applies to lipid-soluble and small uncharged molecules (e.g., O2, CO2)
    • Protein-mediated transport: Facilitated by channel or carrier proteins for charged (ions) or water-soluble molecules
      • Channels: Provide specific pathways for substances to move through the membrane
      • Carriers: Bind to the transported substance, change conformation, and release it on the other side of the membrane
    • Endocytosis: Process of bringing substances into the cell by engulfing them in membrane-bound vesicles:
      • Phagocytosis: Ingestion of large particles, e.g., bacteria
      • Pinocytosis: Ingestion of fluid and small molecules
    • Exocytosis: Process of releasing substances from the cell by fusing vesicles with the plasma membrane

    Movement Across Plasma Membrane

    • Lipid-soluble and small uncharged molecules: Freely diffusible across the membrane, driven by concentration gradient
    • Charged (ions) / water-soluble molecules: Movement is restricted due to the hydrophobic interior of the membrane
    • Selectively permeable membrane: Allows for the control of ion movement across the membrane

    Membrane Potential

    • Separation of charges: Gives rise to "membrane potential" due to attraction between opposite charges (cations (+) and anions (-)) across the membrane.
    • Role in all cells: Cells possess a membrane potential, representing an electrical difference across the membrane
    • Excitable cells: Nerve and muscle cells actively change their membrane potential, forming the basis for their electrical excitability
    • Transport: Used for active transport of substances
    • Mechanism: The membrane acts as a barrier, establishing concentration gradients of key ions across the membrane. The magnitude of the potential depends on the degree of charge separation

    Absence of Membrane Potential

    • Electrically neutral: When there is no charge difference across the membrane, despite the membrane barrier, there is no membrane potential

    Presence of Membrane Potential

    • Separated charges: A charge difference across the membrane, due to the presence of separated charges (cations (+) and anions (-))
    • Remainder of fluid: The remainder of the intracellular and extracellular fluids remain electrically neutral

    Resting Membrane Potential (RMP)

    • Negative inside: The inside of the cell membrane is more negative than the outside.
    • Neuron: Typically -70mV
    • Factors contributing to RMP:
      • Unequal distribution of ions: Differing concentrations of K+, Na+, and large protein anions (A-) inside and outside the cell
      • Selective permeability: The cell membrane is more permeable to K+ than other ions, allowing K+ to leak out of the cell down its concentration gradient

    Distribution of ions responsible for RMP

    • High concentration of K+ inside the cell: 150 mM
    • High concentration of Na+ outside the cell: 150 mM
    • High concentration of A- inside the cell: 65 mM

    Na+/K+ ATPase (Pump)

    • Role: Maintains concentration gradients of K+ and Na+ across the membrane
    • Mechanism: Transports 3 Na+ ions out of the cell and 2 K+ ions into the cell, using energy from ATP (ATP Hydrolysis, creating a "pump")
    • Importance:
      • Establishes concentration gradients for Na+ and K+
      • Contributes to the negative charge inside the cell

    Resting Membrane Potential - Factors Contributing to it

    • Na+/K+ ATPase pump: Transports ions unequally, resulting in slight negative charge inside the cell due to 3Na+ out for 2K+ in
    • Diffusion of K+: Most significant factor; the diffusion of K+ out of the cell down its concentration gradient established by the pump makes the inside more negative

    PM is "Leaky" to K+

    • Ion movement: K+ is constantly moving across the membrane, but cannot fully leak out because of the Na+/K+ ATPase pump constantly working to maintain ion gradients

    Membrane Potential Changes

    • Depolarization: Increase in positivity of the membrane potential (becomes less negative)
    • Hyperpolarization: Increase in negativity of the membrane potential (becomes more negative)
    • Repolarization: Return of the membrane potential to its resting state following depolarization

    Na+-K+ Pump is the Major Driving Force for Transport

    • Coupled Transport: Utilizes the concentration gradient of Na+ (high outside the cell) to drive the transport of other substances into the cell
    • Cotransporters: Proteins that simultaneously move two or more substances in the same direction across the membrane
    • Example: The sodium-glucose cotransporter uses the energy from the movement of Na+ down its concentration gradient to bring glucose into the cell.

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    Test your understanding of the cell membrane's structure and functions, including membrane transport mechanisms such as diffusion, endocytosis, and exocytosis. Dive into concepts like membrane potential and how cells interact with their environment.

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