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Questions and Answers
What are the two main types of transport across the cell membrane?
What are the two main types of transport across the cell membrane?
Lipid-soluble substances can easily pass through the cell membrane.
Lipid-soluble substances can easily pass through the cell membrane.
True
Which of the following is NOT a type of gate protein?
Which of the following is NOT a type of gate protein?
What is the name of the protein that facilitates the diffusion of glucose across the cell membrane?
What is the name of the protein that facilitates the diffusion of glucose across the cell membrane?
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Which type of active transport requires energy directly from the hydrolysis of ATP?
Which type of active transport requires energy directly from the hydrolysis of ATP?
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What type of vesicular transport is responsible for taking in large particles, such as bacteria?
What type of vesicular transport is responsible for taking in large particles, such as bacteria?
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What is the primary function of the sodium-potassium pump?
What is the primary function of the sodium-potassium pump?
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The ______ of a substance can affect its rate of diffusion.
The ______ of a substance can affect its rate of diffusion.
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Which of the following is NOT a factor affecting the rate of diffusion?
Which of the following is NOT a factor affecting the rate of diffusion?
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What is the name of the process by which water moves across a semipermeable membrane from an area of high water concentration to an area of low water concentration?
What is the name of the process by which water moves across a semipermeable membrane from an area of high water concentration to an area of low water concentration?
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Facilitated diffusion requires energy from ATP.
Facilitated diffusion requires energy from ATP.
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What type of carrier protein transports multiple substances in the same direction across the cell membrane?
What type of carrier protein transports multiple substances in the same direction across the cell membrane?
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What is the name of the process by which a cell releases substances into its external environment?
What is the name of the process by which a cell releases substances into its external environment?
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Study Notes
Transport Across Cell Membranes
- The lecture covers transport mechanisms across cell membranes, including passive and active transport.
- Topic Outcomes include describing mechanisms for lipid-soluble and water-soluble molecule diffusion, properties of gated and carrier proteins, primary and secondary active transport, Na+-K+ pump functions, and macromolecule transport (exocytosis and endocytosis).
- ICF and ECF primarily consist of water and dissolved solutes (ions, glucose, amino acids).
- Substances entering a cell include nutrients, ionic salts, oxygen, and water.
- Substances leaving a cell include secretion, nitrogenous waste, oxygen, carbon dioxide, and excess water.
- Cell membranes have a lipid bilayer interspersed with globular proteins.
- Lipid-soluble substances (e.g. gases, fatty acids, alcohol, steroid hormones) pass directly through the lipid bilayer.
- Water-soluble substances (e.g. water, ions, glucose, amino acids) pass through transporter proteins.
- Integral proteins act as transporters, including channel proteins and carrier proteins.
- Transport is classified based on energy requirements: passive (diffusion, osmosis) and active (primary, secondary).
- Vesicular transport includes exocytosis, endocytosis (pinocytosis, phagocytosis, receptor-mediated endocytosis), and transcytosis.
Passive Transport
- Substances move across the membrane without energy expenditure.
- Movement is along a concentration or electrical pressure gradient.
Diffusion
- Movement of solute molecules from a higher to lower concentration until equilibrium is reached.
- This process occurs along chemical, electrical, or pressure gradients.
- Driven by random molecular movement (Brownian motion).
- Uses kinetic energy of matter.
- Diffusion through cell membranes can be simple or facilitated.
Diffusion Through Cell Membranes
- Simple diffusion is for lipid-soluble substances (e.g. O2, CO2, steroids).
- Facilitated diffusion is for water-soluble substances and uses carrier proteins.
Facilitated Diffusion
- The rate of diffusion involves specific carrier membrane proteins.
- Faster than simple diffusion.
- Larger water-soluble substances diffuse using facilitated diffusion if they are unable to pass without this assistance.
Water Channels (Aquaporins)
- Integral membrane proteins facilitating water movement.
- 13 types identified, involved in reabsorption from late distal convoluted tubules.
Ion Channels
- Integral transmembrane proteins regulating ion permeability.
- Selective based on type of ion (e.g., K+, Na+, Ca2+, Cl−).
- Specific types involve different diameter and charges on inner surface and locations of gating mechanisms.
Voltage Gated Channels
- Respond to changes in membrane potential.
- Involved in nerve signal transmission.
Ligand-Gated Channels
- Respond to the binding of a ligand (e.g., neurotransmitter, hormones).
Factors Affecting Diffusion Rate
- Rate is directly proportional to concentration gradient, surface area, and solubility of substance, and inversely proportional to thickness and molecular size.
Osmosis
- Diffusion of pure solvent (water) across a selectively permeable membrane from a region of low to high solute concentration.
- Osmotic pressure is the pressure required to prevent solvent migration.
Osmotic Pressure
- Related to the number of osmotically active particles in a solution, not their size or weight.
- Types include exosmosis and endosmosis.
Active Transport
- Movement of substances against their concentration/electrical gradients.
- Requiring energy input (often ATP).
- Involves carrier proteins (pumps).
- Shows specificity and saturation.
Primary Active Transport
- Energy directly from ATP hydrolysis to power the transport.
- Examples include the sodium-potassium pump, calcium pump, and H+/K+ pump.
Sodium-Potassium Pump
- Transports 3 Na+ ions out and 2 K+ ions into the cell.
- Critical for maintaining resting membrane potential.
- ATPase Activity essential
Mechanism of Operation of Na+/K+ Pump
- Step 1: Binding of 3 Na+ and ATP to the carrier protein inside the cell.
- Hydrolysis of ATP
- Transfer of high energy phosphate group.
- Conformational change, Na+ move out of cell.
- Step 2: Binding of 2 K+ outside.
- Dephosphorylation.
- Conformational change.
- K+ transported into cell.
Functions of Na⁺-K⁺ Pump
- Maintaining cytosolic ionic concentration and cell volume.
- Forming the electrogenic pump that maintains resting membrane potential.
- Storing energy for secondary active transport.
- Protein synthesis
Calcium Pump
- Actively transports calcium ions (Ca2+) out of cells or into organelles.
- Critical for muscle contraction and other calcium-dependent processes.
Hydrogen–Potassium ATPase
- Involved in gastric acid secretion and kidney function.
- Pumps H+ ions (acid) out of cells in exchange for K+.
Secondary Active Transport
- Energy derived from the electrochemical gradient created by primary active transport.
- No direct ATP hydrolysis required.
- Examples include sodium co-transport and sodium counter-transport.
Sodium Co-Transport (Symport)
- Movement of two substances are coupled in the same direction.
- Example includes the transport of glucose and amino acids from intestinal lumen into blood in symport with Na+.
Sodium Counter-Transport (Antiport)
- Movement of two substances in the opposite direction.
- Example includes Na+-Ca++ and Na+-H+ countertransport.
Vesicular Transport
- Bulk transport of large molecules across cell membranes using vesicles.
- Includes endocytosis and exocytosis
Endocytosis
Ingestion of materials by a fold or invagination of the cell membrane to encapsulate it.
- Types of endocytosis:
- Pinocytosis, for small soluble substances.
- Phagocytosis, for larger insoluble particles, such as pathogens or cellular debris.
- Receptor-mediated endocytosis, specific mechanism for target molecule uptake.
Exocytosis
- Secretion of materials by the fusion of vesicles with the cell membrane.
Transcytosis
- Coupled endocytosis and exocytosis.
- Transport across cells (e.g., epithelial cells).
Transport Across Epithelia
- Paracellular transport (between cells).
- Transcellular transport (across cells)
References
- List of Medical Physiology Textbooks (titles).
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Description
This quiz explores the various transport mechanisms across cell membranes, including passive and active transport. It covers lipid-soluble and water-soluble molecule diffusion, gated and carrier proteins, and macromolecule transport through processes like exocytosis and endocytosis. Test your knowledge on essential concepts such as the Na+-K+ pump and the composition of intracellular and extracellular fluid.
