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Questions and Answers
What is the primary reason for the establishment of a concentration gradient across the cell membrane?
What is the primary reason for the establishment of a concentration gradient across the cell membrane?
- To separate and store charge
- To generate energy for the cell
- To maintain the selective permeability of the membrane (correct)
- To facilitate passive transport of molecules
Which of the following best describes the movement of ions across the cell membrane?
Which of the following best describes the movement of ions across the cell membrane?
- They are not affected by their concentration gradient
- They are influenced solely by their concentration gradient
- They are influenced by both their concentration gradient and the electrical gradient (correct)
- They are not affected by the electrical gradient
What is the primary function of the selective permeability of the cell membrane?
What is the primary function of the selective permeability of the cell membrane?
- To facilitate active transport of molecules
- To maintain the concentration gradient across the membrane (correct)
- To separate and store charge
- To regulate the flow of water across the membrane
What is the net movement of water through a selectively permeable membrane?
What is the net movement of water through a selectively permeable membrane?
What percentage of resting energy is used to maintain concentration and electrical gradients?
What percentage of resting energy is used to maintain concentration and electrical gradients?
What is the term for the difference in charged ions between the inside and outside of the membrane?
What is the term for the difference in charged ions between the inside and outside of the membrane?
What is the term for the stored energy represented by the concentration and electrical gradients?
What is the term for the stored energy represented by the concentration and electrical gradients?
What is the analogy used to describe the cell membrane in terms of storing and separating charge?
What is the analogy used to describe the cell membrane in terms of storing and separating charge?
What is the primary function of membrane proteins in the cell membrane?
What is the primary function of membrane proteins in the cell membrane?
Which of the following molecules can permeate the hydrophobic core of the lipid bilayer?
Which of the following molecules can permeate the hydrophobic core of the lipid bilayer?
What is the primary driving force behind diffusion?
What is the primary driving force behind diffusion?
What is the effect of increasing the surface area of a cell on diffusion?
What is the effect of increasing the surface area of a cell on diffusion?
What is the maximum size of a cell that can rely solely on diffusion for transport?
What is the maximum size of a cell that can rely solely on diffusion for transport?
What is the effect of membrane thickness on the rate of diffusion?
What is the effect of membrane thickness on the rate of diffusion?
Which of the following molecules is impermeable to the lipid bilayer?
Which of the following molecules is impermeable to the lipid bilayer?
What is the effect of increasing the temperature on the rate of diffusion?
What is the effect of increasing the temperature on the rate of diffusion?
What is the condition for osmosis to occur across a biological membrane?
What is the condition for osmosis to occur across a biological membrane?
What is the primary function of aquaporins in cell membranes?
What is the primary function of aquaporins in cell membranes?
What is the effect of mercury on the permeability of water through the cell membrane?
What is the effect of mercury on the permeability of water through the cell membrane?
What is the relationship between the permeability of water through the lipid bilayer (Pd) and the permeability of water through water channels (Pf)?
What is the relationship between the permeability of water through the lipid bilayer (Pd) and the permeability of water through water channels (Pf)?
What determines the difference in osmolarity between two solutions?
What determines the difference in osmolarity between two solutions?
What is the effect of temperature on the permeability of water through the lipid bilayer?
What is the effect of temperature on the permeability of water through the lipid bilayer?
What is the definition of osmotic pressure?
What is the definition of osmotic pressure?
What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?
What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?
What is the primary function of proteins in the fluid mosaic model of membrane structure?
What is the primary function of proteins in the fluid mosaic model of membrane structure?
What type of lipid molecules comprise 75% of the lipids in the cell membrane?
What type of lipid molecules comprise 75% of the lipids in the cell membrane?
What is the thickness of the cell membrane?
What is the thickness of the cell membrane?
What is the primary reason for the selective permeability of the cell membrane?
What is the primary reason for the selective permeability of the cell membrane?
What is the primary mechanism of transport across cell membranes?
What is the primary mechanism of transport across cell membranes?
What is the primary function of the lipid bilayer in the cell membrane?
What is the primary function of the lipid bilayer in the cell membrane?
What is the term that describes the movement of substances from an area of higher concentration to an area of lower concentration?
What is the term that describes the movement of substances from an area of higher concentration to an area of lower concentration?
What is the structure of the phospholipid bilayer in the cell membrane?
What is the structure of the phospholipid bilayer in the cell membrane?
What is the primary reason for the asymmetry of lipid composition in membrane leaflets?
What is the primary reason for the asymmetry of lipid composition in membrane leaflets?
What determines the fluidity of a membrane?
What determines the fluidity of a membrane?
Which type of protein is attached to the surface of the cell membrane and is easily removed?
Which type of protein is attached to the surface of the cell membrane and is easily removed?
What is the function of hydrophobic regions in integral membrane proteins?
What is the function of hydrophobic regions in integral membrane proteins?
Which type of molecule is permeable through the lipid bilayer?
Which type of molecule is permeable through the lipid bilayer?
What is the primary function of receptor proteins in the cell membrane?
What is the primary function of receptor proteins in the cell membrane?
What is the result of the molecular organization of the cell membrane?
What is the result of the molecular organization of the cell membrane?
What is the characteristic of hydrophilic regions in integral membrane proteins?
What is the characteristic of hydrophilic regions in integral membrane proteins?
What is the primary reason for the limitation of cell size to approximately 20 μm in diameter?
What is the primary reason for the limitation of cell size to approximately 20 μm in diameter?
What is the effect of increasing the surface area of a cell on diffusion?
What is the effect of increasing the surface area of a cell on diffusion?
What is the effect of temperature on the rate of diffusion?
What is the effect of temperature on the rate of diffusion?
What is the result of a difference in concentration between two sides of a membrane?
What is the result of a difference in concentration between two sides of a membrane?
What is the effect of membrane thickness on the rate of diffusion?
What is the effect of membrane thickness on the rate of diffusion?
Which of the following molecules can diffuse through the hydrophobic core of the lipid bilayer?
Which of the following molecules can diffuse through the hydrophobic core of the lipid bilayer?
What is the primary benefit of increasing the membrane area available for exchange?
What is the primary benefit of increasing the membrane area available for exchange?
What is the result of an increase in the surface area of a cell?
What is the result of an increase in the surface area of a cell?
Which of the following best describes the energy requirement for the maintenance of concentration and electrical gradients across the cell membrane?
Which of the following best describes the energy requirement for the maintenance of concentration and electrical gradients across the cell membrane?
What is the primary driving force behind the movement of ions across the cell membrane?
What is the primary driving force behind the movement of ions across the cell membrane?
What is the term for the difference in charged ions between the inside and outside of the cell membrane?
What is the term for the difference in charged ions between the inside and outside of the cell membrane?
What is the primary consequence of osmosis across a biological membrane?
What is the primary consequence of osmosis across a biological membrane?
What is the primary function of the selectively permeable cell membrane in terms of osmosis?
What is the primary function of the selectively permeable cell membrane in terms of osmosis?
What is the primary reason for the energy storage in concentration and electrical gradients across the cell membrane?
What is the primary reason for the energy storage in concentration and electrical gradients across the cell membrane?
What is the term for the movement of substances from an area of higher concentration to an area of lower concentration?
What is the term for the movement of substances from an area of higher concentration to an area of lower concentration?
What is the primary analogy used to describe the cell membrane in terms of storing and separating charge?
What is the primary analogy used to describe the cell membrane in terms of storing and separating charge?
What is the primary reason for water movement across a biological membrane?
What is the primary reason for water movement across a biological membrane?
Which of the following is a characteristic of Pf, the permeability of water through water channels?
Which of the following is a characteristic of Pf, the permeability of water through water channels?
What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?
What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?
What is the term for the pressure applied to a solution to prevent the inward flow of water across a semi-permeable membrane?
What is the term for the pressure applied to a solution to prevent the inward flow of water across a semi-permeable membrane?
Which of the following determines the difference in osmolarity between two solutions?
Which of the following determines the difference in osmolarity between two solutions?
What is the effect of increasing the temperature on the permeability of water through the lipid bilayer?
What is the effect of increasing the temperature on the permeability of water through the lipid bilayer?
What is the relationship between Pf and Pd?
What is the relationship between Pf and Pd?
Which of the following is a characteristic of the movement of water across a biological membrane?
Which of the following is a characteristic of the movement of water across a biological membrane?
What is the primary mechanism by which cholesterol and glycolipids are scattered among the phospholipid molecules in the cell membrane?
What is the primary mechanism by which cholesterol and glycolipids are scattered among the phospholipid molecules in the cell membrane?
What is the primary consequence of the amphipathic nature of phospholipid molecules in the cell membrane?
What is the primary consequence of the amphipathic nature of phospholipid molecules in the cell membrane?
What is the primary role of membrane proteins in the fluid mosaic model of membrane structure?
What is the primary role of membrane proteins in the fluid mosaic model of membrane structure?
What is the primary driving force behind the movement of substances from an area of higher concentration to an area of lower concentration?
What is the primary driving force behind the movement of substances from an area of higher concentration to an area of lower concentration?
What is the primary consequence of the difference in osmolarity between two solutions separated by a semi-permeable membrane?
What is the primary consequence of the difference in osmolarity between two solutions separated by a semi-permeable membrane?
What is the primary function of the lipid bilayer in the cell membrane?
What is the primary function of the lipid bilayer in the cell membrane?
What is the primary characteristic of facilitated diffusion?
What is the primary characteristic of facilitated diffusion?
What is the primary consequence of increasing the surface area of a cell?
What is the primary consequence of increasing the surface area of a cell?
What is the primary mechanism by which nonpolar, uncharged molecules cross the cell membrane?
What is the primary mechanism by which nonpolar, uncharged molecules cross the cell membrane?
Which type of molecules are permeable through the lipid bilayer due to their lipid solubility?
Which type of molecules are permeable through the lipid bilayer due to their lipid solubility?
What is the primary function of hydrophilic regions in integral membrane proteins?
What is the primary function of hydrophilic regions in integral membrane proteins?
What determines the fluidity of a membrane?
What determines the fluidity of a membrane?
What is the result of the molecular organization of the cell membrane?
What is the result of the molecular organization of the cell membrane?
Which type of protein is attached to the surface of the cell membrane and is easily removed?
Which type of protein is attached to the surface of the cell membrane and is easily removed?
What is the primary function of transporter proteins in the cell membrane?
What is the primary function of transporter proteins in the cell membrane?
What is the primary reason for the asymmetry of lipid composition in membrane leaflets?
What is the primary reason for the asymmetry of lipid composition in membrane leaflets?
What is the primary reason for the difference in permeability of water through the lipid bilayer (Pd) and through water channels (Pf)?
What is the primary reason for the difference in permeability of water through the lipid bilayer (Pd) and through water channels (Pf)?
What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?
What is the result of a difference in osmolarity between two solutions separated by a semi-permeable membrane?
What determines the permeability of water through the lipid bilayer (Pd)?
What determines the permeability of water through the lipid bilayer (Pd)?
What is the primary function of aquaporin isoforms in cell membranes?
What is the primary function of aquaporin isoforms in cell membranes?
What is the primary driving force behind the movement of water across a semi-permeable membrane?
What is the primary driving force behind the movement of water across a semi-permeable membrane?
What determines the rate of diffusion across a cell membrane?
What determines the rate of diffusion across a cell membrane?
What is the result of an increase in the surface area of a cell?
What is the result of an increase in the surface area of a cell?
What is the term that describes the movement of substances from an area of higher concentration to an area of lower concentration?
What is the term that describes the movement of substances from an area of higher concentration to an area of lower concentration?
What is the primary factor that determines the rate of diffusion?
What is the primary factor that determines the rate of diffusion?
Which of the following factors increases the rate of diffusion?
Which of the following factors increases the rate of diffusion?
What is the result of a large concentration gradient across a membrane?
What is the result of a large concentration gradient across a membrane?
What is the effect of increasing the size of the diffusing substance?
What is the effect of increasing the size of the diffusing substance?
What is the primary reason for the limitation of cell size?
What is the primary reason for the limitation of cell size?
What is the effect of increasing the temperature on the rate of diffusion?
What is the effect of increasing the temperature on the rate of diffusion?
What is the effect of increasing the membrane thickness on the rate of diffusion?
What is the effect of increasing the membrane thickness on the rate of diffusion?
What is the primary benefit of increasing the membrane area available for exchange?
What is the primary benefit of increasing the membrane area available for exchange?
What is the primary factor that determines the rate of diffusion across a cell membrane?
What is the primary factor that determines the rate of diffusion across a cell membrane?
What is the effect of increasing the surface area of a cell on the rate of diffusion?
What is the effect of increasing the surface area of a cell on the rate of diffusion?
What is the primary mechanism of transport across cell membranes?
What is the primary mechanism of transport across cell membranes?
What is the primary driving force behind the movement of ions across the cell membrane?
What is the primary driving force behind the movement of ions across the cell membrane?
What is the primary benefit of increasing the membrane area available for exchange?
What is the primary benefit of increasing the membrane area available for exchange?
What is the result of a difference in concentration between two sides of a membrane?
What is the result of a difference in concentration between two sides of a membrane?
What is the primary reason for the limitation of cell size to approximately 20 μm in diameter?
What is the primary reason for the limitation of cell size to approximately 20 μm in diameter?
What is the effect of temperature on the rate of diffusion?
What is the effect of temperature on the rate of diffusion?
What determines the direction of diffusion of non-charged molecules across a cell membrane?
What determines the direction of diffusion of non-charged molecules across a cell membrane?
What is the primary reason for the establishment of an electrical gradient across a cell membrane?
What is the primary reason for the establishment of an electrical gradient across a cell membrane?
Which of the following is a characteristic of the movement of ions across a cell membrane?
Which of the following is a characteristic of the movement of ions across a cell membrane?
What is the primary function of the selective permeability of the cell membrane?
What is the primary function of the selective permeability of the cell membrane?
What determines the rate of diffusion of non-charged molecules across a cell membrane?
What determines the rate of diffusion of non-charged molecules across a cell membrane?
What is the result of the difference in concentration of charged ions between the inside and outside of a cell membrane?
What is the result of the difference in concentration of charged ions between the inside and outside of a cell membrane?
What is the primary driving force behind the movement of non-charged molecules across a cell membrane?
What is the primary driving force behind the movement of non-charged molecules across a cell membrane?
What is the result of the movement of ions down their concentration gradient across a cell membrane?
What is the result of the movement of ions down their concentration gradient across a cell membrane?
What is the primary factor that determines the rate of diffusion across a cell membrane?
What is the primary factor that determines the rate of diffusion across a cell membrane?
What is the effect of increasing the concentration of a substance on one side of a cell membrane?
What is the effect of increasing the concentration of a substance on one side of a cell membrane?
What is the relationship between the concentration gradient and the rate of diffusion across a cell membrane?
What is the relationship between the concentration gradient and the rate of diffusion across a cell membrane?
What is the effect of decreasing the temperature on the rate of diffusion across a cell membrane?
What is the effect of decreasing the temperature on the rate of diffusion across a cell membrane?
What is the primary mechanism by which cells maintain concentration gradients across their cell membranes?
What is the primary mechanism by which cells maintain concentration gradients across their cell membranes?
What is the effect of increasing the surface area of a cell membrane on the rate of diffusion?
What is the effect of increasing the surface area of a cell membrane on the rate of diffusion?
What is the relationship between the concentration gradient and the direction of diffusion across a cell membrane?
What is the relationship between the concentration gradient and the direction of diffusion across a cell membrane?
What is the primary benefit of maintaining a concentration gradient across a cell membrane?
What is the primary benefit of maintaining a concentration gradient across a cell membrane?
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Study Notes
Selective Permeability and Diffusion
- The cell membrane is selectively permeable, allowing certain substances to cross while excluding others
- The lipid bilayer is permeable to nonpolar, uncharged molecules (e.g. O2, N2, benzene) and lipid-soluble molecules (e.g. steroids, fatty acids, some vitamins)
- The lipid bilayer is impermeable to large uncharged polar molecules (e.g. glucose, amino acids) and ions (e.g. Na+, K+, Cl-, Ca2+)
Diffusion
- Diffusion is the random mixing of particles in a solution due to kinetic energy
- Diffusion occurs from an area of high concentration to an area of low concentration
- Factors affecting the rate of diffusion:
- Concentration gradient: the greater the difference in concentration, the faster the rate of diffusion
- Temperature: higher temperatures increase the rate of diffusion
- Particle size: larger particles diffuse slower
- Surface area: increasing surface area increases the rate of diffusion
- Distance: increasing diffusion distance slows down the rate of diffusion
Osmosis
- Osmosis is the diffusion of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration
- Osmosis occurs to eliminate osmotic gradients
- Cell membranes are permeable to water but not to certain solutes, allowing osmosis to occur
Membrane Permeability to Water
- The cell membrane has a permeability coefficient (Pw) that is the sum of two components:
- Pd: permeability through the lipid bilayer, which is small, mercury-insensitive, and temperature-dependent
- Pf: permeability through water channels, which is large, mercury-sensitive, and temperature-independent
- Aquaporins are proteins that mediate Pf, and cells express different isoforms to regulate water permeability
Gradients across the Cell Membrane
- Concentration gradients: non-charged molecules diffuse down their concentration gradients
- Electrical gradients: ions are influenced by the membrane potential in addition to their concentration gradient
- The selective permeability of the membrane enables the establishment of concentration and electrical gradients across the membrane
- Cells maintain concentration and electrical gradients at a cost of energy (~30% of resting energy)
Selective Permeability and Diffusion
- The cell membrane is selectively permeable, allowing certain substances to cross while excluding others
- The lipid bilayer is permeable to nonpolar, uncharged molecules (e.g. O2, N2, benzene) and lipid-soluble molecules (e.g. steroids, fatty acids, some vitamins)
- The lipid bilayer is impermeable to large uncharged polar molecules (e.g. glucose, amino acids) and ions (e.g. Na+, K+, Cl-, Ca2+)
Diffusion
- Diffusion is the random mixing of particles in a solution due to kinetic energy
- Diffusion occurs from an area of high concentration to an area of low concentration
- Factors affecting the rate of diffusion:
- Concentration gradient: the greater the difference in concentration, the faster the rate of diffusion
- Temperature: higher temperatures increase the rate of diffusion
- Particle size: larger particles diffuse slower
- Surface area: increasing surface area increases the rate of diffusion
- Distance: increasing diffusion distance slows down the rate of diffusion
Osmosis
- Osmosis is the diffusion of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration
- Osmosis occurs to eliminate osmotic gradients
- Cell membranes are permeable to water but not to certain solutes, allowing osmosis to occur
Membrane Permeability to Water
- The cell membrane has a permeability coefficient (Pw) that is the sum of two components:
- Pd: permeability through the lipid bilayer, which is small, mercury-insensitive, and temperature-dependent
- Pf: permeability through water channels, which is large, mercury-sensitive, and temperature-independent
- Aquaporins are proteins that mediate Pf, and cells express different isoforms to regulate water permeability
Gradients across the Cell Membrane
- Concentration gradients: non-charged molecules diffuse down their concentration gradients
- Electrical gradients: ions are influenced by the membrane potential in addition to their concentration gradient
- The selective permeability of the membrane enables the establishment of concentration and electrical gradients across the membrane
- Cells maintain concentration and electrical gradients at a cost of energy (~30% of resting energy)
Gradients across the Cell Membrane
- A concentration gradient is the difference in concentration of non-charged molecules between the inside and outside of the cell membrane, causing molecules to diffuse down their concentration gradients.
- An electrical gradient, or membrane potential, is the difference in electrical charge between the inside and outside of the cell membrane, influencing the movement of ions.
- The selective permeability of the cell membrane allows for the establishment of concentration and electrical gradients across the membrane.
- The membrane's selectivity enables cells to maintain differences in charged ions between the inside and outside of the membrane, establishing an electrical gradient.
Ion Gradients across the Membrane
- The concentration of ions (Na+, K+, Cl-) is higher in the extracellular fluid than in the cytoplasm.
- The cell membrane acts as a capacitor, separating and storing charge.
Osmosis
- Osmosis is the diffusion of water through a selectively permeable membrane from an area of high water concentration to an area of low water concentration.
- Osmosis occurs when the membrane is permeable to water but not to certain solutes.
- Water moves to eliminate osmotic gradients.
Membrane Permeability to Water
- The permeability of the cell membrane to water is determined by the presence of aquaporins (9 isoforms) and the lipid bilayer.
- Cells have different permeability to water due to the expression of different aquaporin isoforms.
Selective Membrane Permeability
- The cell membrane is selectively permeable to small uncharged polar molecules (water, urea, glycerol, CO2) and impermeable to large uncharged polar molecules (glucose, amino acids) and ions (Na+, K+, Cl-, Ca2+, H+).
- Membrane proteins mediate the transport of substances across the membrane that cannot permeate the hydrophobic core of the lipid bilayer.
Diffusion
- Diffusion is the random mixing of particles in a solution as a result of kinetic energy.
- The rate of diffusion is influenced by the concentration gradient, temperature, and surface area.
- Diffusion is limited by the size of the cell (approximately 20 µm).
Membrane Fluidity
- Membranes are fluid structures, and lipids can move around within the plane of the membrane.
- Fluidity is determined by lipid tail length, number of double bonds, and the amount of cholesterol.
Membrane Proteins
- Integral proteins extend into or across the cell membrane and are amphipathic, with hydrophobic regions spanning the hydrophobic core of the lipid bilayer.
- Peripheral proteins are attached to the inner or outer surface of the cell membrane and are easily removed.
- Membrane proteins can act as receptors, cell identity markers, linkers, enzymes, ion channels, and transporter proteins.
Selective Permeability of Membrane
- The molecular organization of the membrane results in selective permeability, allowing some substances to cross while excluding others.
- The lipid bilayer is permeable to nonpolar, uncharged molecules and lipid-soluble molecules.
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