Membrane Structure and Function
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Questions and Answers

What triggers the phosphorylation of the sodium-potassium pump?

  • High concentration of Na+ outside the cell
  • Release of ADP
  • Binding of K+ to the pump
  • Binding of Na+ to the pump (correct)

During the function of the sodium-potassium pump, what occurs after Na+ is expelled from the cell?

  • K+ binds to the protein and restores its original conformation (correct)
  • The pump remains inactive until K+ is removed
  • ADP releases another phosphate group
  • Na+ can bind to the pump again immediately

What is the initial condition of the sodium and potassium concentrations before the pump operates?

  • [Na+] is low in the cytoplasm and [K+] is also low
  • [Na+] and [K+] are both balanced across the membrane
  • [Na+] is high outside the cell and [K+] is low in the cytoplasm (correct)
  • [Na+] is low in the cytoplasm and [K+] is high outside the cell

What is the role of ATP in the sodium-potassium pump mechanism?

<p>It provides energy for phosphorylation. (A)</p> Signup and view all the answers

What happens to the sodium-potassium pump when K+ binds to the extracellular side?

<p>The protein's conformation changes, leading to the release of phosphate. (B)</p> Signup and view all the answers

What is the primary function of receptors in receptor-mediated endocytosis?

<p>To select specific extracellular compounds (C)</p> Signup and view all the answers

What triggers the formation of vesicles during receptor-mediated endocytosis?

<p>Binding of ligands to receptors (C)</p> Signup and view all the answers

Which component is likely involved in the formation of coated pits during receptor-mediated endocytosis?

<p>Coat proteins (D)</p> Signup and view all the answers

What term describes a molecule that binds specifically to a receptor molecule in receptor-mediated endocytosis?

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

In receptor-mediated endocytosis, what is the role of the coated vesicle?

<p>To transport specific compounds into the cell (A)</p> Signup and view all the answers

What structural feature distinguishes endocytosis as receptor-mediated?

<p>Presence of coated pits (A)</p> Signup and view all the answers

How do ligands enter the cell during receptor-mediated endocytosis?

<p>Through vesicles formed by receptor-ligand binding (D)</p> Signup and view all the answers

What is the significance of ligand-receptor binding in receptor-mediated endocytosis?

<p>It initiates vesicle formation (B)</p> Signup and view all the answers

What is the primary function of the CTR-1 protein?

<p>Absorbing copper in intestinal epithelial cells (B)</p> Signup and view all the answers

What type of genetic inheritance pattern is associated with CTR-1 deficiency?

<p>Autosomal recessive (D)</p> Signup and view all the answers

What is the result when water moves from a hypotonic solution to a hypertonic solution?

<p>An isotonic equilibrium is reached (A)</p> Signup and view all the answers

What can be a symptom of CTR-1 deficiency?

<p>Severe developmental delay (D)</p> Signup and view all the answers

Which of the following best describes osmosis?

<p>Movement of water through a semipermeable membrane (A)</p> Signup and view all the answers

What is the primary role of the proton pump in the cotransport process?

<p>To maintain a higher concentration of H+ outside the cell (A)</p> Signup and view all the answers

In the example of cotransport described, what energy source is used to maintain the H+ gradient?

<p>Energetic ATP hydrolysis (C)</p> Signup and view all the answers

How does the sucrose-H+ cotransporter function in this transport mechanism?

<p>It relies on the potential energy of the H+ gradient to import sucrose (C)</p> Signup and view all the answers

What type of transport is represented by the movement of H+ through the proton pump?

<p>Active transport (C)</p> Signup and view all the answers

What happens to the gradient of H+ ions when ATP is utilized by the proton pump?

<p>The gradient is maintained, keeping H+ concentration high outside the cell (A)</p> Signup and view all the answers

What is the ultimate benefit of the H+ gradient established by the proton pump?

<p>To create potential energy that drives the cotransport of sucrose (D)</p> Signup and view all the answers

Which process describes the movement of H+ ions into the cell through diffusion?

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

Why is the transport of sucrose dependent on the movement of H+ ions?

<p>The energy from H+ movement allows sucrose to be transported against its gradient (D)</p> Signup and view all the answers

Which of the following descriptions correctly defines phagocytosis?

<p>The mechanism by which cells take in solid particles or bacteria. (C)</p> Signup and view all the answers

What is the role of pseudopodia in phagocytosis?

<p>To aid in the movement and engulfing of particles. (C)</p> Signup and view all the answers

How does pinocytosis differ from phagocytosis?

<p>Pinocytosis is the uptake of fluids, while phagocytosis is focused on solid particles. (A)</p> Signup and view all the answers

What size range do phagocytosis and pinocytosis generally involve for the particles being engulfed?

<p>Phagocytosis typically deals with particles in the micrometer range, while pinocytosis deals with sub-micrometer particles. (B)</p> Signup and view all the answers

In which cellular process would one expect to see vesicles forming at the plasma membrane?

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

What is the primary requirement for active transport to occur?

<p>It requires energy, usually in the form of ATP. (C)</p> Signup and view all the answers

Which of the following describes the direction of substance movement in active transport?

<p>From low concentration to high concentration. (A)</p> Signup and view all the answers

What type of membrane proteins are primarily responsible for active transport?

<p>Ion pumps. (A)</p> Signup and view all the answers

What effect does active transport have on the concentration gradients within cells?

<p>It maintains concentration gradients that differ from surroundings. (A)</p> Signup and view all the answers

Which of the following is a specific type of active transport system?

<p>Sodium-potassium (Na+/K+) pump. (B)</p> Signup and view all the answers

Which of the following correctly distinguishes active transport from passive transport?

<p>Active transport requires energy to move substances against a gradient. (B)</p> Signup and view all the answers

What is the role of ATP in active transport?

<p>To provide energy necessary for transport. (D)</p> Signup and view all the answers

Active transport primarily functions to:

<p>Allow cells to control internal concentrations of substances. (D)</p> Signup and view all the answers

Flashcards

CTR-1

A protein responsible for absorbing copper (Cu+2) from the intestines.

CTR-1 deficiency

A genetic condition caused by mutations in the CTR-1 gene. It disrupts copper absorption, leading to various health problems.

Osmosis

Movement of water across a semipermeable membrane from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic).

Hypotonic

A solution with a lower solute concentration compared to another solution. Water will move from a hypotonic solution to a hypertonic solution.

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Hypertonic

A solution with a higher solute concentration compared to another solution. Water will move from a hypotonic solution to a hypertonic solution.

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Sodium-potassium pump

A protein that pumps sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, using energy from ATP.

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Active transport

The process of the sodium-potassium pump moving sodium out of the cell and potassium inside the cell.

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ATP's role in the sodium-potassium pump

ATP (adenosine triphosphate) is the energy source used by the sodium-potassium pump.

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Conformational change

The sodium-potassium pump changes its shape to move sodium and potassium across the cell membrane.

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Sodium binding to the pump

The cytoplasmic Na+ binds to the sodium-potassium pump, initiating the pumping action.

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ATP

Energy molecule used by cells for various processes, including active transport.

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Concentration Gradient

The difference in concentration of a substance between two areas.

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Ion Pumps

Specific membrane proteins that use energy to pump ions across a membrane.

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Sodium-potassium (Na+/K+) Pump

An active transport system that moves sodium ions out of the cell and potassium ions into the cell, maintaining the cell's electrochemical gradient.

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Passive Transport

The movement of substances across a cell membrane without requiring energy.

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Diffusion

A type of passive transport where substances move across a membrane from a region of high concentration to a region of low concentration.

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Phagocytosis

A type of endocytosis where cells engulf large particles, such as bacteria or cellular debris, by wrapping them in their plasma membrane and forming a vesicle.

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Pinocytosis

A form of endocytosis where cells take in small droplets of extracellular fluid by creating tiny vesicles from their plasma membrane.

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Pseudopodia

Finger-like projections of the plasma membrane that extend outward to engulf the target particle during phagocytosis.

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Vesicle

A membrane-bound sac formed during endocytosis to enclose the engulfed substance.

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Endocytosis

Process where a cell takes in materials from its surroundings by enclosing them in a membrane-bound vesicle.

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Cotransport

A type of membrane transport where the movement of one molecule across the membrane is coupled to the movement of another molecule in the same direction.

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Proton pump

A protein that actively pumps protons (H+) across the cell membrane, creating a proton gradient.

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Proton gradient

The energy stored in the difference in concentration of protons (H+) across the cell membrane.

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Cotransporter

A protein that facilitates the movement of two molecules across the membrane simultaneously, often one molecule moving down its concentration gradient and the other moving against it.

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Receptor-mediated endocytosis

A process where cells take in specific molecules from their environment using receptors.

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Ligand

A molecule that binds to a receptor on the cell surface.

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Receptor

A protein that binds to a specific ligand on the cell surface, triggering the formation of a vesicle.

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Coat protein

A protein that coats the outside of a vesicle during receptor-mediated endocytosis.

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Coated pit

A region of the plasma membrane that is coated with coat proteins and receptors, where vesicles bud off.

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Vesicle formation

The process by which a coated pit pinches off from the plasma membrane to form a coated vesicle.

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Uncoating

The process by which a coated vesicle loses its coat protein and fuses with other organelles inside the cell.

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Study Notes

Membrane Structure and Function

  • The plasma membrane separates the living cell from its non-living surroundings
  • The plasma membrane is a fluid mosaic of lipids and proteins
  • The fluid mosaic model was proposed by Singer and Nicolson in 1972
  • The membrane is a fluid structure with a "mosaic" of various proteins embedded within it
  • The membrane is composed of a phospholipid bilayer and proteins embedded within it
  • Phospholipids are amphipathic, consisting of hydrophilic "heads" and hydrophobic "tails"
  • Phospholipids spontaneously create bilayers in an aqueous environment
  • Phospholipids form micelles or liposomes in aqueous environments
  • Micelles are single-layer spherical structures
  • Liposomes are bilayer spherical structures, used for efficient delivery of drugs/compounds to cells
  • Membrane lipids include phospholipids, glycolipids, and sterols
  • Phospholipids can be either phosphoglycerides or phosphosphingolipids
  • Phosphoglycerides are based on glycerol + 2 fatty acids + phosphate + organic molecule
  • Phosphosphingolipids are based on sphingosine + 1 fatty acid + phosphate + organic molecule
  • Cholesterol, a steroid alcohol, is found in animal cell membranes
  • Phytosterols are found in plant cell membranes
  • Ergosterol is found in fungal and protozoal cell membranes
  • Membrane proteins determine most of the membrane's functions
  • These proteins are embedded within the lipid bilayer
  • Membrane proteins come in integral and peripheral types
  • Integral proteins completely span the membrane, or are attached to a membrane lipid
  • Peripheral proteins are loosely bound to the membrane
  • Integral transmembrane proteins span the cell membrane one or more times
  • This type of protein penetrates the hydrophobic core of the lipid bilayer
  • Examples of transmembrane proteins are growth factor receptors (EGFR), insulin, ẞ-barrel: e.g. bacterial porin
  • Lipid-bound proteins are attached to a membrane lipid
  • Examples of lipid-bound proteins are hydrolases, receptors
  • Peripheral membrane proteins are loosely bound to the membrane and interact with the polar surface of the membrane or with proteins imbedded in the membrane
  • Examples of peripheral proteins are erythrocyte spectrin
  • Transmembrane proteins can have various functions including transportation, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and extracellular matrix
  • Membrane carbohydrates include glycoproteins, glycolipids, and proteoglycans
  • Glycocalyx is the carbohydrate cover on the external side of the cell membrane, protecting the cell surface from mechanical/chemical damage
  • The human blood cell types A, B, AB, and O reflect variation in RBC surface carbohydrates There are 2 types of passive transport: diffusion and osmosis
  • Diffusion is the tendency of any substance to spread out evenly in the available space
  • Active transport moves substances against their concentration gradient, and requires energy often in the form of ATP
  • Cells can maintain concentration gradients that differ from their surroundings
  • Active transport is performed by specialized membrane proteins, called ion pumps
  • The sodium-potassium pump (Na+/K+) is one example
  • Osmosis is the movement of water across a semipermeable membrane
  • Osmosis is affected by the concentration gradient
  • Water molecules will move from an area of low solute / higher water concentration to an area with a higher solute / lower water concentration
  • Three conditions can describe osmosis which are isotonic, hypertonic, and hypotonic
  • The term isotonic means that the concentration of solutes in the solution is the same as it is inside the cell and there will be no net movement of water
  • The term hypertonic means that the concentration of solutes in the solution is greater than in the cell, and the cell will lose water
  • The term hypotonic means that the concentration of solutes in the solution is less than in the cell, and the cell will gain water
  • Three examples of bulk transport are phagocytosis, pinocytosis, and receptor-mediated endocytosis
  • In phagocytosis a cell engulfs a solid particle (macromolecule or microorganism) in a vacuole, which fuses with a lysosome
  • Phagocytes are specialized immune cells that can engulf microorganisms
  • In pinocytosis, soluble molecules enter the cell when extracellular fluid is taken up into tiny vesicles
  • Receptor-mediated endocytosis is a type of endocytosis in which specific molecules are taken up when a binding ligand to a receptor triggers vesicle formation, for example the process of cholesterol uptake by hepatocytes

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