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Questions and Answers
What primarily determines osmotic pressure in a solution?
What primarily determines osmotic pressure in a solution?
Which characteristic is NOT a peculiar feature of carrier mediated transport?
Which characteristic is NOT a peculiar feature of carrier mediated transport?
In which type of solution will RBCs swell and possibly undergo hemolysis?
In which type of solution will RBCs swell and possibly undergo hemolysis?
Which of the following accurately describes Fick's Law of Diffusion?
Which of the following accurately describes Fick's Law of Diffusion?
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Which statement about facilitated diffusion is true?
Which statement about facilitated diffusion is true?
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What is the primary cause of hemolysis in red blood cells?
What is the primary cause of hemolysis in red blood cells?
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In the Gibbs-Donnan equilibrium, which ions are described as non-diffusible?
In the Gibbs-Donnan equilibrium, which ions are described as non-diffusible?
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What factors contribute to the Vmax in carrier mediated transport?
What factors contribute to the Vmax in carrier mediated transport?
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What does a negative Gibbs free energy (ΔG) indicate about a system's process?
What does a negative Gibbs free energy (ΔG) indicate about a system's process?
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Which factors are considered in Fick's Law of diffusion?
Which factors are considered in Fick's Law of diffusion?
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Which mechanism of transport allows for the diffusion of larger, water-soluble molecules?
Which mechanism of transport allows for the diffusion of larger, water-soluble molecules?
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In the context of diffusion, which statement about the permeability of the membrane is true?
In the context of diffusion, which statement about the permeability of the membrane is true?
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What is the effect of increasing the concentration gradient on the rate of diffusion as per Fick’s Law?
What is the effect of increasing the concentration gradient on the rate of diffusion as per Fick’s Law?
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Which of the following best describes the Gibbs-Donnan Equilibrium?
Which of the following best describes the Gibbs-Donnan Equilibrium?
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How does increasing the thickness of the membrane affect the net rate of diffusion according to Fick's Law?
How does increasing the thickness of the membrane affect the net rate of diffusion according to Fick's Law?
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Which type of channel is specifically activated by the binding of a molecule in facilitated diffusion?
Which type of channel is specifically activated by the binding of a molecule in facilitated diffusion?
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What role does Gibbs Free Energy play in the process of active transport?
What role does Gibbs Free Energy play in the process of active transport?
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According to Fick's Law of Diffusion, which factor does NOT affect the rate of diffusion across a membrane?
According to Fick's Law of Diffusion, which factor does NOT affect the rate of diffusion across a membrane?
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Facilitated diffusion primarily differs from simple diffusion in that it requires:
Facilitated diffusion primarily differs from simple diffusion in that it requires:
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Which statement regarding osmotic pressure is accurate?
Which statement regarding osmotic pressure is accurate?
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Gibbs-Donnan Equilibrium is characterized by:
Gibbs-Donnan Equilibrium is characterized by:
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The primary active transport mechanism is specifically known for:
The primary active transport mechanism is specifically known for:
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Which of the following substances is commonly transported by primary active transport mechanisms?
Which of the following substances is commonly transported by primary active transport mechanisms?
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Which characteristic is NOT associated with facilitated diffusion?
Which characteristic is NOT associated with facilitated diffusion?
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Study Notes
Cell Membrane
- Surrounds entire cell and organelles
- Fluid in nature, molecules move
- Phospholipid bilayer:
- Head - polar/hydrophilic
- Tail - nonpolar/hydrophobic
- Proteins:
- Integral - carrier and channel proteins
- Peripheral - receptors and antigens
Functions of Cell Membrane
- Semi-permeable barrier (selective)
- Maintains differences in ICF and ECF composition and fluid composition in organelles
- Protects cells from toxic substances
- Excretes waste products
- Transports nutrients
- Receives signals from outside:
- Chemical signals
- Electrical signals
- Site for attachment to neighboring cells
Transport Through Cell Membrane
- Essential for cellular life
- Necessary for exchange for cell function
- Involves incorporation of biological molecules and discharge of waste products
- Movement of particles (solute) across a membranous barrier
- Dependent on membrane permeability, transmembrane solute concentration, and solute size/charge
- Three mechanisms: passive, facilitated, and active transport
- Some mechanisms require energy and a transmembrane protein, while others do not
Transport Mechanisms
-
Passive:
- Simple diffusion
- Facilitated diffusion
- Filtration
- Osmosis
- Dialysis
-
Active:
- Primary active transport
- Secondary active transport
- Endocytosis/Exocytosis
Methods of Transport
-
Passive:
-
Diffusion:
- Simple (lipid bilayer, protein channels)
- Osmosis
- Filtration
- Dialysis
-
Diffusion:
-
Active
- Leaky channels
- Voltage gated channels
- Ligand gated channels
Simple Diffusion
- Movement of molecules from higher to lower concentration until equilibrium is reached.
- Can occur through lipid bilayer or protein channels.
- Factors affecting rate: lipid solubility, molecular size/weight, temperature, membrane thickness, surface area, concentration gradient, pressure gradient, and electrical gradient.
Diffusion Through Lipid Bilayer
- Lipid-soluble substances (O2, CO2, alcohols, steroids)
- Lipid-insoluble substances (water, urea, sugar) diffuse through spaces between lipids.
- Electrolytes are generally impermeable due to charge and size.
Protein Channels
- Open/leaky channels (Na+, K+)
- Gated channels: open under specific conditions (ligand-gated, voltage-gated, etc.).
- Na+, K+, Ca++ channels.
- Channel mutations can cause channelopathies (e.g., muscle and brain disorders).
Factors Affecting Rate of Diffusion
- Lipid solubility
- Molecular size and weight
- Temperature
- Thickness of the membrane
- Surface area
- Concentration gradient
- Pressure gradient
- Electrical gradient
Gibbs-Donnan Equilibrium
- Explains concentration differences in diffusible ions across a semipermeable membrane when one compartment contains nondiffusible ions.
- Proteins are non-diffusible anions.
- Concentration of Na+ is higher in compartment A compared to compartment B.
Osmosis & Osmotic Pressure
- Water movement across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.
- Osmotic pressure is the minimum pressure required to prevent osmosis.
- Depends on the total number of particles of solute, not the type of particle
- Osmoles (mOsmols) express the concentration of osmotically active particles (e.g. total number of particles in 1 gram molecular weight of a molecule dissolved 1 kg of water
Applied Solutions
- Isotonic: Fluids have the same osmolarity as plasma (290 mOsmols); red blood cells neither shrink nor swell in isotonic solutions. Ex. 0.9% NaCl, 5% glucose solutions.
- Hypotonic: RBC swell and hemolysis (bursting) may occur.
- Hypertonic: RBC shrink due to water moving out.
Filtration in Capillaries
- Fluid and solute movement through a membrane due to pressure difference
- Arterial end: Filtration pressure > osmotic pressure --> fluid moves out.
- Mid-capillary: Pressures are balanced.
- Venous end: Osmotic pressure > filtration pressure --> fluid reenters.
Dialysis
- Separation of larger from smaller particles to remove waste products in cases of renal failure.
Active Transport
- Primary active transport
- Requires energy (ATP)
- Examples: Na+-K+ pump, Ca++ pump, H+-K+ pump
- Carrier protein has ATPase activity, which, when activated, hydrolyzes ATP, releasing energy that causes a conformational change in the carrier protein.
- Secondary active transport
- Uses the electrochemical gradient established by primary active transport
- Endocytosis
- Pinocytosis - all cells
- Receptor-mediated endocytosis- Highly selective to transport specific large molecules, requiring energy and calcium. E.g., low-density lipoproteins, viruses
- Phagocytosis - specialized cells, internalizing large multimolecular particles like bacteria. Forms pseudopodia to engulf and bring material into the cell.
Peculiarities of Active Transport
- Carrier-mediated transport
- Rapid rate of transport
- Against electrochemical gradient (uphill)
- Expenditure of energy by ATPase activity of the carrier protein
- Carrier protein shows specificity, saturation, competitive inhibition, and blocking.
Active Transport, Summary
- Na+-K+ pump (example) - ATP hydrolysis - conformational change- movement of ions.
- Regulators: hormones, conc. of ions
Types of Transporters
- Uniporters - Transport one molecule in one direction
- Symporters - Transport two molecules in the same direction
- Antiporters - Transport two molecules in opposite directions
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Description
Explore the structure and functions of the cell membrane in this quiz. Learn about the phospholipid bilayer, membrane proteins, and various transport mechanisms essential for cellular life. Test your knowledge on how cell membranes maintain homeostasis and communicate with external signals.
