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Questions and Answers
What component of cell membranes primarily aids in creating barrier functions?
What component of cell membranes primarily aids in creating barrier functions?
Which of the following describes simple diffusion?
Which of the following describes simple diffusion?
What characteristics do ligand-gated channels possess?
What characteristics do ligand-gated channels possess?
Which factor does NOT affect the rate of diffusion across a cell membrane?
Which factor does NOT affect the rate of diffusion across a cell membrane?
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What type of transport requires the expenditure of energy?
What type of transport requires the expenditure of energy?
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What type of transport moves molecules against their concentration gradient utilizing energy?
What type of transport moves molecules against their concentration gradient utilizing energy?
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What is osmotic pressure primarily related to?
What is osmotic pressure primarily related to?
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Which of the following best describes an isotonic solution?
Which of the following best describes an isotonic solution?
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Which statement is true about osmosis?
Which statement is true about osmosis?
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What is the definition of osmolarity?
What is the definition of osmolarity?
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Which mechanism would utilize a sodium-potassium pump?
Which mechanism would utilize a sodium-potassium pump?
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What happens to the osmotic pressure when solute concentration increases?
What happens to the osmotic pressure when solute concentration increases?
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In which type of transport are specific carrier proteins necessary?
In which type of transport are specific carrier proteins necessary?
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What is the primary function of the Na K ATPase pump?
What is the primary function of the Na K ATPase pump?
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What occurs during the binding of Na and K to the Na K ATPase pump?
What occurs during the binding of Na and K to the Na K ATPase pump?
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What type of transport is exemplified by Na+/glucose co-transport?
What type of transport is exemplified by Na+/glucose co-transport?
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Which statement correctly describes counter-transport?
Which statement correctly describes counter-transport?
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What is phagocytosis primarily used for?
What is phagocytosis primarily used for?
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How does exocytosis differ from endocytosis?
How does exocytosis differ from endocytosis?
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What mechanism is used to maintain the concentration gradients of Na and K across the cell membrane?
What mechanism is used to maintain the concentration gradients of Na and K across the cell membrane?
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Which of the following describes pinocytosis?
Which of the following describes pinocytosis?
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Study Notes
Cell Membrane Structure
- Composed primarily of lipids and proteins.
- The lipid component includes phospholipids, cholesterol, and glycolipids.
Protein Functions
- Essential for various cellular activities including:
- Transport across the membrane
- Structural support
- Communication with other cells
- Enzymatic activity
Passive Transport
- Movement of substances across the membrane without energy expenditure.
- Includes:
- Simple diffusion
- Facilitated diffusion
- Osmosis
Simple Diffusion
- Kinetic movement of molecules or ions through the lipid bilayer membrane.
- Occurs through intermolecular spaces or membrane openings.
- Rate of diffusion depends on:
- Concentration gradient
- Velocity of kinetic motion of molecules
- Number and sizes of openings in the cell membrane.
Simple Diffusion Through Protein Channels
- Occurs through integral cell membrane proteins, often open pathways.
- Pores provide selective permeability based on size and electrical charge.
- Channels are highly selective for ions.
- Channels have gates, regulated by electrical signals (voltage-gated channels) or chemical binding (ligand-gated channels).
Facilitated Diffusion
- Movement of substances with the aid of a specific carrier protein.
- Used for relatively large organic molecules like glucose and amino acids.
Osmosis
- Net diffusion of water across a membrane due to a water concentration difference.
- Water moves from a region of high water concentration to a region of low water concentration.
- The concentration of water is inversely related to the number of solute particles, regardless of particle size.
Osmotic Pressure
- The pressure required to prevent osmosis.
- Related to the number of particles in solution, not their mass.
- Higher solute concentration = Higher osmotic pressure.
Osmolarity and Osmolality
- Osmolarity: Number of osmoles per liter of solution.
- Osmolality: Number of osmoles per kg of solution.
- Normal osmolarity of body fluids: 290 mosm/L
Isotonic, Hypertonic, and Hypotonic Solutions
- Isotonic solution: Same solute concentration as extracellular fluid.
- Hypertonic solution: Higher solute concentration than extracellular fluid.
- Hypotonic solution: Lower solute concentration than extracellular fluid.
Active transport
- Movement of substances against their concentration gradient, requiring energy.
- Utilizes specific carrier proteins.
Types of Active Transport
- Primary active transport
- Secondary active transport
- Co-transport (symport)
- Counter-transport (antiport)
Primary Active Transport
- Sodium-Potassium Pump (Na+/K+ ATPase):
- Pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell against their concentration gradients.
- Requires ATP for energy.
- Maintains the concentration gradient of Na+ and K+, crucial for nerve cell functions and other excitable cells.
Secondary Active Transport
- Uses the energy stored in the concentration gradients created by primary active transport to move other molecules or solutes.
- Two solutes bind to the same transporter protein.
- One solute moves along its concentration gradient, providing energy for the other solute to move against its gradient.
Co-transport (Symport)
- Two solutes move in the same direction.
- Examples: Na+/glucose co-transport, Na+/amino acids co-transport.
Counter-transport (Antiport)
- Two solutes move in opposite directions.
- Examples: Na+/Ca+ counter-transport, Na+/H+ counter-transport.
Endocytosis and Exocytosis
- Mechanisms for transporting large molecules, particles, or fluid droplets across the cell membrane.
Endocytosis
- Bringing substances into the cell.
- Types:
- Phagocytosis (cell eating): Engulfing large particles like bacteria, damaged cells, tissue debris.
- Pinocytosis (cell drinking): Transporting proteins, fats, and extracellular fluid.
Exocytosis
- Releasing substances from the cell.
- Membrane-bound vesicles in the cytoplasm fuse with the plasma membrane and release their contents to the extracellular fluid.
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